December  2017

Updated:   3 December 2017


Best wishes for the festive season to all readers


Welcome to the night skies of Summer, featuring Pegasus, Andromeda, Cetus, Aquarius, Taurus and Orion


Note:  Some parts of this webpage may be formatted incorrectly by older browsers.


The Alluna RC-20 Ritchey Chrétien telescope was installed in March, 2016.

The telescope is able to locate and track any sky object (including Earth satellites and the International Space Station) with software called TheSkyX Professional, into which is embedded a unique T-Point model developed for our site with our equipment over the past year.


Explanatory Notes:  


Times for transient sky phenomena are given using a 24 hour clock, i.e. 20:30 hrs = 8.30 pm. Times are in Australian Eastern Standard Time (AEST), which equals Universal Time (UT) + 10 hours. Daylight saving is not observed in Queensland. Observers in other time zones will need to make their own corrections where appropriate. With conjunctions of the Moon, planets and stars, timings indicate the closest approach. Directions (north or south) are approximate. The Moon’s diameter is given in arcminutes ( ’ ). The Moon is usually about 30’ or half a degree across. The 'limb' of the Moon is its edge as projected against the sky background.

Rise and set times are given for the theoretical horizon, which is a flat horizon all the way round the compass, with no mountains, hills, trees or buildings to obscure the view. Observers will have to make allowance for their own actual horizon. 

Transient phenomena are provided for the current month and the next. Geocentric phenomena are calculated as if the Earth were fixed in space as the ancient Greeks believed. This viewpoint is useful, as otherwise rising and setting times would be meaningless. In the list of geocentric events, the nearer object is given first.

When a planet is referred to as ‘stationary’, it means that its movement across the stellar background appears to have ceased, not that the planet itself has stopped. With inferior planets (those inside the Earth’s orbit, Mercury and Venus), this is caused by the planet heading either directly towards or directly away from the Earth. With superior planets (Mars out to Pluto), this phenomenon is caused by the planet either beginning or ending its retrograde loop due to the Earth’s overtaking it.

Apogee and perigee:   Maximum and minimum distances of the Moon or artificial satellite from the Earth.

Aphelion and perihelion:  Maximum and minimum distances of a planet, asteroid or comet from the Sun.

A handspan at arm's length covers an angle of approximately 18 - 20 degrees.

mv = visual magnitude or brightness. Magnitude 1 stars are very bright, magnitude 2 less so, and magnitude 6 stars are so faint that the unaided eye can only just detect them under good, dark conditions. Binoculars will allow us to see down to magnitude 8, and the Observatory telescope can reach visual magnitude 17 or 22 photographically. The world's biggest telescopes have detected stars and galaxies as faint as magnitude 30. The sixteen very brightest stars are assigned magnitudes of 0 or even -1. The brightest star, Sirius, has a magnitude of -1.44. Jupiter can reach -2.4, and Venus can be more than 6 times brighter at magnitude -4.7, bright enough to cast shadows. The Full Moon can reach magnitude -12 and the overhead Sun is magnitude -26.5. Each magnitude step is 2.51 times brighter or fainter than the next one, i.e. a magnitude 3.0 star is 2.51 times brighter than a magnitude 4.0. Magnitude 1.0 stars are exactly 100 times brighter than magnitude 6.0 (5 steps each of 2.51 times, 2.51x2.51x2.51x2.51x2.51 = 2.515 = 100).


The Four Minute Rule:   

How long does it take the Earth to complete one rotation? No, it's not 24 hours - that is the time taken for the Sun to cross the meridian on successive days. (The meridian is an imaginary semicircular line running from the due south point on the horizon and arching overhead through the zenith, and coming down to the horizon again at its due north point.) This 24 hours is a little longer than one complete rotation, as the curve in the Earth's orbit means that it needs to turn a fraction more (~1 degree of angle) in order for the Sun to cross the meridian again. It is called a 'solar day'. The stars, clusters, nebulae and galaxies are so distant that most appear to have fixed positions in the night sky on a human time-scale, and for a star to return to the same point in the sky relative to a fixed observer takes 23 hours 56 minutes 4.0916 seconds. This is the time taken for the Earth to complete exactly one rotation, and is called a 'sidereal day'.

As our clocks and lives are organised to run on solar days of 24 hours, and the stars circulate in 23 hours 56 minutes approximately, there is a four minute difference between the movement of the Sun and the movement of the stars. This causes the following phenomena:

    1.    The Sun slowly moves in the sky relative to the stars by four minutes of time or one degree of angle per day. Over the course of a year it moves ~4 minutes X 365 days = 24 hours, and ~1 degree X 365 = 360 degrees or a complete circle. Together, both these facts mean that after the course of a year the Sun returns to exactly the same position relative to the stars, ready for the whole process to begin again.

    2.    For a given clock time, say 8:00 pm, the stars on consecutive evenings are ~4 minutes or ~1 degree further on than they were the previous night. This means that the stars, as well as their nightly movement caused by the Earth's rotation, also drift further west for a given time as the weeks pass. The stars of autumn, such as Orion are lost below the western horizon by mid-June, and new constellations, such as Sagittarius, have appeared in the east.  The stars change with the seasons, and after a year, they are all back where they started, thanks to the Earth's having completed a revolution of the Sun and returned to its theoretical starting point.

We can therefore say that the star patterns we see in the sky at 11:00 pm tonight will be identical to those we see at 10:32 pm this day next week (4 minutes X 7 = 28 minutes earlier), and will be identical to those of 9:00 pm this date next month or 7:00 pm the month after. All the above also includes the Moon and planets, but their movements are made more complicated, for as well as the Four Minute Drift  with the stars, they also drift at different rates against the starry background, the closest ones drifting the fastest (such as the Moon or Venus), and the most distant ones (such as Saturn or Neptune) moving the slowest.



 Solar System


Sun:   The Sun begins the month in the non-zodiacal constellation of Ophiuchus, the Serpent Bearer.  It crosses into Sagittarius, the Archer on December 18.



Total Lunar Eclipse, January 31:

There will be a total lunar eclipse visible from south-east Queensland on Wednesday, January 31 next. All aspects of the eclipse will be visible. The Full Moon will enter the Earth's penumbra at 8:49 pm when it is about 26 degrees above the east-north-eastern horizon. This phase is hardly noticeable. The eclipse proper will begin at 9:50 pm, when the Moon begins to enter the Earth's main shadow, which is called the umbra. Even the most casual observer will see a bite appearing out of the edge of the Moon. The Full Moon will gradually lose its brightness as more of it disappears into our shadow. By 10:54 pm the bright Moon will be completely immersed in the shadow, but it will still be faintly visible as a reddish disc. This is the total phase of the eclipse, and mid-eclipse occurs at 11:30 pm. After that the Moon will very slowly brighten, and totality will end at 7 minutes after midnight. Then the western edge of the Moon will begin to come out of the umbra, and the whole Moon will again be visible by 1:10 am. The Moon will still take another hour to leave the penumbra, and the eclipse will be over by 2:14 am. Before and after a lunar eclipse, the Full Moon looks brighter than normal, as the Sun, Moon and Earth are so perfectly aligned. Before and after a lunar eclipse, the Full Moon looks brighter than normal, as the Sun, Moon and Earth are so perfectly aligned.

 It is perfectly safe to watch lunar eclipses as they occur at night. Solar eclipses are the dangerous ones, for looking at the Sun without special eye protection can ruin your eyesight. They are not rare, but quite uncommon. The last total lunar eclipse visible from Starfield Observatory occurred on April 4, 2015. If you miss this one for any reason, you will need to wait until May 26, 2021 for the next.


Moon Phases:  Lunations (Brown series):  #1175, 1176 


Full Moon:               December 04           01:47 hrs          diameter = 33.4'      Supermoon   
Last Quarter:           Decem
ber 10           17:52 hrs          diameter = 31.3' 
New Moon:             
December 18          16:31 hrs         diameter = 29.4'    
First Quarter:          
December 26          19:20 hrs          diameter = 31.0' 

Full Moon:               January 02               12:24 hrs          diameter = 33.5'      Supermoon
Last Quarter:          
January 09               08:26 hrs          diameter = 30.7' 
New Moon:              
January 17               12:17 hrs          diameter = 29.5'
First Quarter:           January 25               08:20 hrs          diameter = 31.6'
Full Moon:               January 31               23:27 hrs          diameter = 33.2'      Total lunar eclipse

'Supermoons' are Full Moons which occur when the Moon is at its closest to Earth, or perigee. This makes the Full Moon fractionally larger and brighter than normal. This happens occasionally, but is not a rare occurrence. It will happen this month and next month, the Full Moon being almost 8% wider and 16% brighter than average.



Lunar Orbital Elements:

December 04:       Moon at perigee (357 505 km) at 19:08 hrs, diameter = 33.4'
December 08:       Moon at ascending node at 10:38 hrs, diameter = 32.4'
December 19:       Moon at apogee (406 601 km) at 12:03 hrs, diameter = 29.4'
December 22:       Moon at descending node at 20:05 hrs, diameter = 29.7'

January 02:           Moon at perigee (356 584 km) at 07:36 hrs, diameter = 33.5'
January 04          Moon at ascending node at 17:52 hrs, diameter = 33.0'
January 15:           Moon at apogee (406 466 km) at 12:31 hrs, diameter = 29.4'
January 19:           Moon at descending node at 00:27 hrs, diameter = 29.7'
January 30:          
Moon at perigee (358 986 km) at 19:30 hrs, diameter = 33.3'

Moon at 8 days after New, as on December 27.

The photograph above shows the Moon when approximately eight days after New, just after First Quarter.  A detailed map of the Moon's near side is available here.  A rotatable view of the Moon, with ability to zoom in close to the surface (including the far side), and giving detailed information on each feature, may be downloaded  here.

Click here for a photographic animation showing the lunar phases. It also shows the Moon's wobble or libration, and how its apparent size changes as it moves from perigee to apogee each month. It takes a little while to load, but once running is very cool !  All these downloads are freeware, although the authors do accept donations if the user feels inclined to support their work.



Lunar Feature for this Month:


Each month we describe a lunar crater, cluster of craters, valley, mountain range or other object, chosen at random, but one with interesting attributes. A recent photograph from our Alluna RC20 telescope will illustrate the object. As all large lunar objects are named, the origin of the name will be given if it is important. This month we will look at a cluster of volcanoes on the Moon near the crater Hortensius.

The crater Hortensius is the large crater filled with shadow towards the lower left-hand corner of the image. It is 15 km in diameter. A crater of a similar size, Hortensius E, is near the southern (bottom) margin, just right of centre. Molten lava flowing across the Moon's surface has breached the north wall of Hortensius E and has flooded the interior, almost filling it up and creating a flat floor.

The mountains in the northern (upper) part of the image form the southern ramparts of the Mare Imbrium, or Sea of Rains. They are called the Montes Carpatus or Carpathian Mountains. Like all the mountains forming the border of the Mare, they were formed during the Imbrium Event, a major collision when a large asteroid struck the Moon's northern hemisphere 3,8 billion years ago. A much later impact struck just off the image's top right-hand corner, creating the crater Copernicus (between the blue lines in the picture below). The blast from this impact radiated in all directions, causing damage to the moonscape from the base surge of molten rock and tumbling masses of stone as big as city blocks. Some of this radial damage can be seen in the image above, trending from the upper-right corner towards the lower margin.

There is a fine cluster of eight volcanoes, most with vents at their summits,  just north of the crater Hortensius. They are seen to be domes averaging 8 to 12 km in diameter, but very low for their size, having heights ranging between 300 and 400 metres. The image includes at least four other volcanic domes apart from those in the cluster, scattered around the image. Can you find them ?  The photograph was taken at Starfield on August 2, 2017.


Ever since people began to look at the Moon through telescopes, they have wondered about the myriads of circular indentations which are found all over its surface. Some of these are very large, over 200 kilometres in diameter. Many are in the range of 50 to 150 kilometres across, and can be seen with even a very small telescope. There are thousands in the range of 10 to 50 kilometres, and even the areas of the Moon that look reasonably flat and featureless are themselves peppered with depressions down to a few metres across, covering every part of the surface.

The first people to make maps of the Moon thought that these hollowed-out features were rings of mountains, or possibly volcanoes. In the early 1660s there was an English scientist Robert Hooke, a man who always thought 'outside the square' and who with Christopher Wren rebuilt the City of London in seven years after the Great Fire of 1666 destroyed it. Robert felt that the Moon might have been hot and soft in the past, and bombarded by large rocks flying through space. In 1664 he experimented with this theory by dropping lead balls into softened pipeclay, to see if the circular depressions on the Moon were formed by impacts. Though encouraged by the results, he felt that the impact theory could not be feasible, as the Moon looked quite hard, not soft like pipeclay, and he was not aware of any flying objects in space that might collide with the Moon. The discovery of asteroids was still 136 years in the future.

He boiled gypsum alabaster in pans (melting point ≈150º C), and when it cooled the surface was covered with circular pits like those on the Moon. He therefore decided that the circular depressions could be made by bubbles of gas welling up in the past from inside a hot and molten Moon, then bursting and quickly cooling and hardening. These would leave cup-like depressions with raised rims. On the other hand, they could indeed be volcanic vents like similar ones on Earth. He described these experiments in the final six pages of his book, Micrographia of 1665. His ideas were thought to be feasible up until about sixty years ago.

High resolution photographs of the Moon taken by satellites in lunar orbits have shown that most of the craters are indeed caused by impacts. The name 'crater' (Latin for 'cup') was given to these depressions by Johann Hieronymus Schröter in his book of lunar drawings published in 1791. Yet there are also many volcanoes on the Moon. Most are in the form of low domes, less than 500 metres high, but distinguished from other hills by their circular shape and the presence of one or more volcanic vents at the summits. There are several hundred on the near side of the Moon, dotted all over the surface but usually in clusters. The cluster shown above is one of the best, with another two clusters not far away to the north-west, one group near the crater Milichius and another near the crater Tobias Mayer.

The best time to observe these domes is when they are close to the terminator (the sunrise or sunset line). At such times the angle of sunlight is very small, i.e. the Sun is just rising above the Moon's horizon. This produces shadows which reveal the elevated nature of the domes, which are generally less than 500 metres high. As the Sun rises over the Moon, the shadows diminish and soon disappear entirely, the only remaining features to be observed being the tiny crater vents at the top of most of them. These vents rarely exceed 1000 metres in diameter.

Other examples of lunar vulcanism are the ash volcanoes in which dark ash has been ejected from vents found in fractures or clefts in crater floors, where the ash does not build up into a dome but instead makes a dark halo around the vent. The best examples of these are the ten found in the crater Alphonsus. Many other craters such as Atlas, Sulpicius Gallus and Gaudibert have large areas showing pyroclastic activity. The Apollo 17 astronauts landed in the Taurus-Littrow pyroclastic area.

Although there have been sporadic reports of 'mists', 'clouds', 'obscurations' and 'red glows' associated with these domes, vents and pyroclastic areas, there have been no confirmed observations of current volcanic activity on the Moon.



This crater is named after Martin van den Hove (1605-1639), a Dutch astronomer and mathematician. It is the Latinised form of his surname, which was given to the crater by Riccioli. Van den Hove was one of the first observers to use a telescope to measure the angular diameters of planets.


 The Hortensius area shown above is defined by the yellow rectangle, and the 95 km crater Copernicus is between the two blue lines.

Click  here  for the  Lunar Features of the Month Archive.

Geocentric Events:


It should be remembered that close approaches of Moon, planets and stars are only perspective effects as seen from the Earth - that is why they are called 'geocentric or Earth-centred phenomena'. The Moon, planets and stars do not really approach and dance around each other as it appears to us from the vantage point of our speeding planet.


December 03:       Mercury at eastern stationary point at 17:31 hrs
December 03:       Neptune at eastern quadrature at 21:46 hrs
December 03:       Moon 1.5º north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 22:41 hrs
December 04:       Venus 23 arcminutes south of the star Graffias (Beta1 Scorpii, mv= 2.56) at 12:43 hrs
December 04:       Moon 1.2º south of the star Zeta Tauri (mv= 2.97) at 21:48 hrs
December 07:       Mercury 1.2º south of Saturn at 12:49 hrs
December 09:       Moon 1.5º north of the star Regulus (Alpha Leonis, mv= 1.36) at 10:58 hrs
December 12:       Mercury at perihelion at 21:41 hrs
December 13:       Mercury at inferior conjunction at 11:11 hrs
December 14:       Moon 4.5º north of Mars at 04:03 hrs
December 15:       Moon 4.7º north of Jupiter at 01:42 hrs
December 15:       Mercury 2.2º north of Venus at 23:58 hrs
December 17:       Moon 2.2º north of of Mercury at 20:06 hrs
December 18:       Moon 3.4º north of Saturn at 23:25 hrs
December 20:       Moon 1.3º north of the star Pi Sagittarii (mv= 2.88) at 07:51 hrs
December 20:       Moon 2º north of Pluto at 12:47 hrs
December 22:       Summer solstice at 02:25 hrs
December 22:       Saturn in conjunction with the Sun at 07:18 hrs
December 22:       Saturn 1.3º north of the star 4 Sagittarii (mv= 4.74) at 07:53 hrs
December 23:       Jupiter 42 arcminutes north of the star Zuben Elgenubi (Alpha Librae, mv= 2.75) at 05:39 hrs
December 23:       Mercury at western stationary point at 11:46 hrs
December 23:       Moon 2.1º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 10:43 hrs
December 25:       Limb of Moon 27 arcminutes south of Neptune at 00:33 hrs
December 26:       Venus 1.1º south of Saturn at 03:29 hrs
December 28:       Moon 3.6º south of Uranus at 06:38 hrs
December 28:       Neptune 32 arcminutes south of the star Lambda Aquarii (mv= 3.73) at 18:35 hrs
December 30:       Venus 1.3º north of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82) at 20:23 hrs
December 31:       Limb of Moon 37 arcminutes north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 10:24 hrs


January 1:            Moon 1.6º south of the star Zeta Tauri (mv= 2.97) at 10:31 hrs
January 2:            Mercury at Greatest Elongation West (22º 35') at 10:36 hrs (diameter = 6.6")
January 2:            Uranus at eastern stationary point ar 22:45 hrs
January 3:            Mars 33 arcminutes north of the star Zuben Elgenubi (Alpha Librae, mv= 2.75) at 06:34 hrs
January 4:            Earth at perihelion at 02:13 hrs
January 4:            Venus 2.9º north of the star Nunki (Sigma Sagittarii, mv= 2.04) at 22:29 hrs
January 5:            Moon 1.2º north of the star Regulus (Alpha Leonis, mv= 1.36) at 17:21 hrs
January 7:            Mars 12 arcminutes south of Jupiter at 09:16 hrs
January 7:            Venus 2.1º south of the star Pi Sagittarii (mv= 2.88) at 17:46 hrs
January 9:            Venus in superior conjunction at 06:27 hrs  (diameter = 9.7")
January 9:            Venus 1.2º south of Pluto at 19:07 hrs
January 9:            Pluto in conjunction at 19:30 hrs  (diameter = 0.1")
January 11:          Moon 4.6º north of Jupiter at 18:59 hrs
January 11:          Moon 5º north of Mars at 22:04 hrs
January 13:          Mercury 38 arcminutes south of Saturn at 14:52 hrs
January 14:          Saturn 1.2º north of the star 11 Sagittarii (mv= 4.96) at 14:56 hrs
January 15:          Uranus at eastern quadrature at 06:38 hrs  (diameter = 3.5")
January 15:          Moon 2.7º north of Saturn at 12:44hrs
January 15:          Moon 3.8º north of Mercury at 18:37 hrs
January 16:          Mercury 2º north of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82) at 09:47 hrs
January 16:          Moon 2.5º north of Pluto at 21:32 hrs
January 16:          Moon 1.4º north of the star Pi Sagittarii (mv= 2.88) at 16:45 hrs
January 17:          Moon 2.9º north of Venus at 18:03 hrs
January 19:          Moon 2.4º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 19:25 hrs
January 20:          Mercury 2.8º north of the star Nunki (Sigma Sagittarii, mv= 2.04) at 14:18 hrs
January 21:          Moon 1.2º south of Neptune at 05:28 hrs
January 23:          Mercury 2.4º south of the star Pi Sagittarii (mv= 2.88) at 07:13 hrs
January 23:          Venus at aphelion at 16:55 hrs  (diameter = 9.8")
January 24:          Moon 4.2º south of Uranus at 12:36 hrs
January 25:          Mercury 1.5º south of Pluto at 07:31 hrs
January 25:          Mercury at aphelion at 21:21 hrs  (diameter = 5.0")
January 27:          Moon 1.3º north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 20:17 hrs
January 28:          Moon 1.1º south of the star Zeta Tauri (mv= 2.97) at 20:53 hrs
January 31:          Mars 2.6º north of the star Delta Scorpii (mv= 2.29) at 12:31 hrs
January 31:          Total Lunar eclipse at 23:30 hrs  (totality from 22:52 to 00:09 hrs - see above)


The Planets for this month:   


Mercury:    On December 1, Mercury will be in the evening sky, being about a handspan above the Sun at sunset, and quite easy to observe. It will be about three degrees above and to the left of Saturn. During the first week of December Mercury will be rapidly catching up to the Earth, and lessening its angular distance from the Sun. It will appear in the telescope as a small crescent. Mercury will pass by Saturn on December 7, becoming progressively closer to the solar glare and harder to observe. It will overtake us, passing between the Earth and the Sun on December 13. After that it will move to the morning sky, rising before the Sun. It should become visible before dawn in the last week of 2017.


Venus:  This, the brightest planet, is still located in the pre-dawn sky as a 'morning star', but it is now so close to the Sun that it is swamped by the glare. However, while a telescope may reveal it, looking so close to the Sun is extremely dangerous, as an accidental flash of sunlight through a telescope can instantaneously ruin your eyesight in that eye.  As December progresses, the angular distance of Venus from the Sun will diminish day by day. On December 1 it will be less than ten degrees (half a handspan) from the Sun, and very difficult to observe due to the solar glare. It is on the far side of its orbit, about as far from the Earth as it can get, and its diameter is only 10 arcseconds. Venus will pass behind the Sun (superior conjunction) on January 9 next year. After that, it will return to the western sky as an 'evening star', becoming readily visible in March 2018. In December, Venus will appear in a small telescope as a tiny 'Full Moon' with a magnitude of -3.9 and a phase of 99%.

(The coloured fringes to the first and third images below are due to refractive effects in our own atmosphere, and are not intrinsic to Venus. The planet was closer to the horizon when these images were taken than it was for the second photograph, which was taken when Venus was at its greatest elongation from the Sun).

                           April 2017                              June 2017                         December 2017                      

Click here for a photographic animation showing the Venusian phases. Venus is always far brighter than anything else in the sky except for the Sun and Moon. For the first two months of 2017, Venus appeared as an 'Evening Star', but on March 25 it moved to the pre-dawn sky and became a 'Morning Star'. Each of these appearances lasts about eight to nine months. Venus will pass on the far side of the Sun (superior conjunction) on January 9, 2018, when it will return to the evening sky and become an 'Evening Star' once again.

Because Venus was visible as the 'Evening Star' and as the 'Morning Star', astronomers of ancient times believed that it was two different objects. They called it Hesperus when it appeared in the evening sky and Phosphorus when it was seen before dawn. They also realised that these objects moved with respect to the so-called 'fixed stars' and so were not really stars themselves, but planets (from the Greek word for 'wanderers'). When it was finally realised that the two objects were one and the same, the two names were dropped and the Greeks applied a new name Aphrodite (Goddess of Love)  to the planet, to counter Ares (God of War). We use the Roman versions of these names, Venus and Mars, for these two planets.


Mars:   Having passed through conjunction with the Sun on July 27, the red planet is becoming easier to observe this month. On December 1 it will be two and a half handspans from the Sun, in the constellation Virgo close by the star Spica. As the weeks pass it will increase its angular separation from the Sun and will grow in size each day, as our Earth, travelling faster, begins to catch it up. On March 25 next year Mars will reach western quadrature, when it rises at midnight. At that time it will have moved into Sagittarius, and will be close to Saturn in the sky. We will overtake Mars on July 27 next year. This will be a very favourable opposition, as Mars will appear bigger (24.2 arcseconds in diameter) and brighter (magnitude -2.8) than it has for many years. It will be particularly favourable for us in the southern hemisphere, as during the month of opposition it will be in the constellation of Capricornus, almost directly overhead each night from the Sunshine Coast. Next winter will be an excellent time for planet observing, with Mars, Jupiter and Saturn all available each evening and high overhead.

In mid-December Mars will rise at about 2 am, but at this time is will be very small with an angular diameter of only 4 arcseconds. Its brightness will be magnitude 1.8. Mars will be the brightest object near the waning crescent Moon on the morning of December 15.

In this image, the south polar cap of Mars is easily seen. Above it is a dark triangular area known as Syrtis Major. Dark Sinus Sabaeus runs off to the left, just south of the equator. Between the south polar cap and the equator is a large desert called Hellas. The desert to upper left is known as Aeria, and that to the north-east of Syrtis Major is called Isidis Regio.  Photograph taken in 1971.

Mars photographed from Starfield Observatory, Nambour on June 29 and July 9, 2016, showing two different sides of the planet.  The north polar cap is prominent.


Brilliant Mars at left, shining at magnitude 0.9, passes in front of the dark molecular clouds in Sagittarius on October 15, 2014. At the top margin is the white fourth magnitude star 44 Ophiuchi. Its type is A3 IV:m. Below it and to the left is another star, less bright and orange in colour. This is the sixth magnitude star SAO 185374, and its type is K0 III. To the right (north) of this star is a dark molecular cloud named B74. A line of more dark clouds wends its way down through the image to a small, extremely dense cloud, B68, just right of centre at the bottom margin. In the lower right-hand corner is a long dark cloud shaped like a figure 5. This is the Snake Nebula, B72. Above the Snake is a larger cloud, B77. These dark clouds were discovered by Edward Emerson Barnard at Mount Wilson in 1905. He catalogued 370 of them, hence the initial 'B'. The bright centre of our Galaxy is behind these dark clouds, and is hidden from view. If the clouds were not there, the galactic centre would be so bright that it would turn night into day.


Jupiter:   We have lost this gas giant planet as a spectacular evening object, as it passed on the far side of the Sun (conjunction) on October 27. It has now moved to the eastern pre-dawn sky, rising before the Sun, In mid-December it will be in the constellation Libra, rising at about 2:30 am.

Jupiter as photographed from Nambour on the evening of April 25, 2017. The images were taken, from left to right, at 9:10, 9:23, 9:49, 10:06 and 10:37 pm. The rapid rotation of this giant planet in a little under 10 hours is clearly seen. In the southern hemisphere, the Great Red Spot (bigger than the Earth) is prominent, sitting within a 'bay' in the South Tropical Belt. South of it is one of the numerous White Spots. All of these are features in the cloud tops of Jupiter's atmosphere.

Jupiter as it appeared at 7:29 pm on July 2, 2017. The Great Red Spot is in a similar position near Jupiter's eastern limb (edge) as in the fifth picture in the series above. It will be seen that in the past two months the position of the Spot has drifted when compared with the festoons in the Equatorial Belt, so must rotate around the planet at a slower rate. In fact, the Belt enclosing the Great Red Spot rotates around the planet in 9 hours 55 minutes, and the Equatorial Belt takes five minutes less. This high rate of rotation has made the planet quite oblate. The prominent 'bay' around the Red Spot in the five earlier images appears to be disappearing, and a darker streak along the northern edge of the South Tropical Belt is moving south. Two new white spots have developed in the South Temperate Belt, west of the Red Spot. The five upper images were taken near opposition, when the Sun was directly behind the Earth and illuminating all of Jupiter's disc evenly. The July 2 image was taken just four days before Eastern Quadrature, when the angle from the Sun to Jupiter and back to the Earth was at its maximum size. This angle means that we see a tiny amount of Jupiter's dark side, the shadow being visible around the limb of the planet on the left-hand side, whereas the right-hand limb is clear and sharp. Three of Jupiter's Galilean satellites are visible, Ganymede to the left and Europa to the right. The satellite Io can be detected in a transit of Jupiter, sitting in front of the North Tropical Belt, just to the left of its centre. 


Saturn:   The ringed planet is very low in the west as twilight fades on December 1, being only one handspan from the Sun. The waxing crescent Moon will be close by Saturn on December 18, but both will be swamped by the solar glare. Saturn will be in conjunction with the Sun on December 22.


Left: Saturn showing the Rings when edge-on.    Right: Over-exposed Saturn surrounded by its satellites Rhea, Enceladus, Dione, Tethys and Titan - February 23/24, 2009.

Saturn with its Rings wide open on July 2, 2017. The shadow of its globe can just be seen on the far side of the Ring system. There are three main concentric rings: Ring A is the outermost, and is separated from the brighter Ring B by a dark gap known as the Cassini Division, which is 4800 kilometres wide, enough to drop Australia through. Ring A also has a gap inside it, but it is much thinner. Called the 'Encke Gap', it is only 325 kilometres wide and can be seen in the image above.The innermost parts of Ring B are not as bright as its outermost parts. Inside Ring B is the faint Ring C, almost invisible but noticeable where it passes in front of the bright planet as a dusky band. Spacecraft visiting Saturn have shown that there are at least four more Rings, too faint and tenuous to be observable from Earth, and some Ringlets. Some of these extend from the inner edge of Ring C to Saturn's cloudtops. The Rings are not solid, but are made up of countless small particles, 99.9% water ice with some rocky material, all orbiting Saturn at different distances and speeds. The bulk of the particles range in size from dust grains to car-sized chunks. At bottom centre, the southern hemisphere of the planet can be seen showing through the gap of the Cassini Division. The ring system extends from 7000 to 80 000 kilometres above Saturn's equator, but its thickness varies from only 10 metres to 1 kilometre. The globe of Saturn has a diameter at its equator of 120 536 kilometres. Being made up of 96% hydrogen and 3% helium, it is a gas giant, although it has a small, rocky core. There are numerous cloud bands visible.

The photograph above was taken when Saturn was close to opposition, with the Earth between Saturn and the Sun. At that time, the shadow of Saturn's globe upon the Ring system was directly behind the planet and hardly visible. The photograph below was taken on September 18, 2017, when Saturn was near eastern quadrature. At such a time, the angle from the Sun to Saturn and back to the Earth is near its maximum, making the shadow fall at an angle across the Rings as seen from Earth. It may be seen falling across the far side of the Ring to the left side of the globe.


Uranus:  This ice giant planet is well placed for viewing this month, as it reached opposition (being in the opposite direction to the Sun, rising in the east as the Sun sets in the west) on October 20. In the weeks around opposition, a planet is visible all night long. Uranus shines at about magnitude 5.8, so a pair of binoculars or a small telescope is required to observe it. It is currently in the constellation Pisces, near the south-west corner of Aries. The waxing gibbous Moon will be in the vicinity of Uranus on December 27 and 28.


Neptune:   The icy blue planet is an early evening object this month. It reached opposition on September 5, and at 8 pm on December 1 it is about two handspans west-north-west of the zenith. Neptune is located in the constellation of Aquarius, between the magnitude 3 star Skat (Delta Aquarii) and the four-star asterism known as the Water-Jar. As it shines at about magnitude 8, a small telescope is required to observe Neptune. The First Quarter Moon will be close to Neptune on the evening of November 27.

Neptune, photographed from Nambour on October 31, 2008

 The erstwhile ninth and most distant planet cannot be observed this month, as it is almost aligned with the Sun. Pluto's angular diameter is 0.13 arcseconds, less than one twentieth that of Neptun
e. Located just east of the 'Teaspoon' which is north-east of the Sagittarius 'Teapot', it is a faint 14.1 magnitude object near the centre of Sagittarius.
This month it is within 1.3 degrees of the magnitude 2.88 star Pi Sagittarii. A telescope with an aperture of 25 cm or more is necessary to observe Pluto.
Pluto will be in conjunction with the Sun on January 9 next.



The movement of the dwarf planet Pluto in two days, between 13 and 15 September, 2008. Pluto is the one object that has moved.
Width of field:   200 arcseconds

This is a stack of four images, showing the movement of Pluto over the period October 22 to 25, 2014. Pluto's image for each date appears as a star-like point at the upper right corner of the numerals. The four are equidistant points on an almost-straight line. Four eleventh magnitude field stars are identified.  A is GSC 6292:20, mv = 11.6.  B is GSC 6288:1587, mv = 11.9.  C is GSC 6292:171, mv = 11.2.  D is GSC 6292:36, mv = 11.5.  (GSC = Guide Star Catalogue).   The position of Pluto on October 24 (centre of image) was at Right Ascension = 18 hours 48 minutes 13 seconds,  Declination =  -20º 39' 11".  The planet moved 2' 51" with respect to the stellar background during the three days between the first and last images, or 57 arcseconds per day, or 1 arcsecond every 25¼ minutes.



Planetary Alignments:

On January 7 Mars and Jupiter will have a close encounter in the sky, being only 15 arcminutes apart in the hours before dawn. On January 13 and 14, Mercury and Saturn will be less than a degree apart. By early April, Mars will have caught up to Saturn.




Meteor Showers:

Phoenicids              December 6/7                         Waning gibbous Moon, 89% sunlit                        ZHR = 6
                                 Radiant:  Near the star Achernar

Geminids                December 14/15                      Waning crescent Moon, 15% sunlit                                            ZHR = 90
Near the star Castor.    Associated with Asteroid 3200 Phaethon.    This will be quite a rich meteor shower.

Ursids                     December 23/24                      Waxing crescent Moon, 20% sunlit                       ZHR = 20
                                 Radiant: Near the star Kochab, in the northern constellation Ursa Minor.

Use this
 Fluxtimator  to calculate the number of meteors predicted per hour for any meteor swarm on any date, for any place in the world.

ZHR = zenithal hourly rate (number of meteors expected to be observed at the zenith in one hour). The maximum phase of meteor showers usually occurs between 3 am and sunrise. The reason most meteors are observed in the pre-dawn hours is because at that time we are on the front of the Earth as it rushes through space at 107 000 km per hour (30 km per second). We are meeting the meteors head-on, and the speed at which they enter our atmosphere is the sum of their own speed plus ours. In the evenings, we are on the rear side of the Earth, and many meteors we see at that time are actually having to catch us up. This means that the speed at which they enter our atmosphere is less than in the morning hours, and they burn up less brilliantly.

Although most meteors are found in swarms associated with debris from comets, there are numerous 'loners', meteors travelling on solitary paths through space. When these enter our atmosphere, unannounced and at any time, they are known as 'sporadics'. Oan average clear and dark evening, an observer can expect to see about ten meteors per hour. They burn up to ash in their passage through our atmosphere. The ash slowly settles to the ground as meteoric dust. The Earth gains about 80 tonnes of such dust every day, so a percentage of the soil we walk on is actually interplanetary in origin. If a meteor survives its passage through the air and reaches the ground, it is called a 'meteorite'.  In the past, large meteorites (possibly comet nuclei or small asteroids) collided with the Earth and produced huge craters which still exist today. These craters are called 'astroblemes'. Two famous ones in Australia are Wolfe Creek Crater and Gosse's Bluff. The Moon and Mercury are covered with such astroblemes, and craters are also found on Venus, Mars, planetary satellites, minor planets, asteroids and even comets.





Comet Lulin

This comet, (C/2007 N3), discovered in 2007 at Lulin Observatory by a collaborative team of Taiwanese and Chinese astronomers, is now in the outer Solar System, and has faded below magnitude 15.

Comet Lulin at 11:25 pm on February 28, 2009, in Leo. The brightest star is Nu Leonis, magnitude 5.26.


The LINEARrobotic telescope operated by Lincoln Near Earth Asteroid Research is used to photograph the night skies, searching for asteroids which may be on a collision course with Earth. It has also proved very successful in discovering comets, all of which are named ‘Comet LINEAR’ after the centre's initials. This name is followed by further identifying letters and numbers. Generally though, comets are named after their discoverer, or joint discoverers. There are a number of other comet and near-Earth asteroid search programs using robotic telescopes and observatory telescopes, such as:
Catalina Sky Survey, a consortium of three co-operating surveys, one of which is the Australian Siding Springs Survey (below),
Siding Spring Survey, using the 0.5 metre Uppsala Schmidt telescope at Siding Spring Observatory, N.S.W., to search the southern skies,
LONEOS, (Lowell Observatory Near-Earth Object Search), concentrating on finding near-Earth objects which could collide with our planet,
Spacewatch, run by the Lunar and Planetary Laboratory of the University of Arizona,
Ondrejov, run by Ondrejov Observatory of the Academy of Sciences in the Czech Republic, 
Xinglong, run by Beijing Astronomical Observatory 

Nearly all of these programs are based in the northern hemisphere, leaving gaps in the coverage of the southern sky. These gaps are the areas of sky where amateur astronomers look for comets from their backyard observatories.

To find out more about current comets, including finder charts showing exact positions and magnitudes, click here. To see pictures of these comets, click here.

The 3.9 metre Anglo-Australian Telescope (AAT) at the Australian Astronomical Observatory near Coonabarabran, NSW.




Deep Space



Sky Charts and Maps available on-line:

There are some useful representations of the sky available here. The sky charts linked below show the sky as it appears to the unaided eye. Stars rise four minutes earlier each night, so at the end of a week the stars have gained about half an hour. After a month they have gained two hours. In other words, the stars that were positioned in the sky at 8 pm at the beginning of a month will have the same positions at 6 pm by the end of that month. After 12 months the stars have gained 12 x 2 hours = 24 hours = 1 day, so after a year the stars have returned to their original positions for the chosen time. This accounts for the slow changing of the starry sky as the seasons progress.

The following interactive sky charts are courtesy of Sky and Telescope magazine. They can simulate a view of the sky from any location on Earth at any time of day or night between the years 1600 and 2400. You can also print an all-sky map. A Java-enabled web browser is required. You will need to specify the location, date and time before the charts are generated. The accuracy of the charts will depend on your computer’s clock being set to the correct time and date.

To produce a real-time sky chart (i.e. a chart showing the sky at the instant the chart is generated), enter the name of your nearest city and the country. You will also need to enter the approximate latitude and longitude of your observing site. For the Sunshine Coast, these are:

latitude:   26.6o South                      longitude:   153o East

Then enter your time, by scrolling down through the list of cities to "Brisbane: UT + 10 hours". Enter this one if you are located near this city, as Nambour is. The code means that Brisbane is ten hours ahead of Universal Time (UT), which is related to Greenwich Mean Time (GMT), the time observed at longitude 0o, which passes through London, England. Click here to generate these charts.


Similar real-time charts can also be generated from another source, by following this second link:

Click here for a different real-time sky chart.

The first, circular chart will show the full hemisphere of sky overhead. The zenith is at the centre of the circle, and the cardinal points are shown around the circumference, which marks the horizon. The chart also shows the positions of the Moon and planets at that time. As the chart is rather cluttered, click on a part of it to show that section of the sky in greater detail. Also, click on Update to make the screen concurrent with the ever-moving sky.

The stars and constellations around the horizon to an elevation of about 40o can be examined by clicking on

View horizon at this observing site

The view can be panned around the horizon, 45 degrees at a time. Scrolling down the screen will reveal tables showing setup and customising options, and an Ephemeris showing the positions of the Sun, Moon and planets, and whether they are visible at the time or not. These charts and data are from YourSky, produced by John Walker.

The charts above and the descriptions below assume that the observer has a good observing site with a low, flat horizon that is not too much obscured by buildings or trees. Detection of fainter sky objects is greatly assisted if the observer can avoid bright lights, or, ideally, travel to a dark sky site. On the Sunshine Coast, one merely has to travel a few kilometres west of the coastal strip to enjoy magnificent sky views. On the Blackall Range, simply avoid streetlights. Allow your eyes about 15 minutes to become dark-adapted, a little longer if you have been watching television. Small binoculars can provide some amazing views, and with a small telescope, the sky’s the limit.

November is not a good month to observe the Eta Carinae Nebula, as it is very low in the south or below Nambour's horizon until the hours after midnight. It will become visible as an evening object again, early in 2018.




The Stars and Constellations for this month:



These descriptions of the night sky are for 10 pm on December 1 and 8 pm on December 31. Broadly speaking, the following description starts in the west and heads east, then south, then high in the south.  


Setting on the western horizon is the zodiacal constellation Capricornus, the Sea Goat.  Above it is Aquarius, the Water Bearer, in which the planet Neptune is located. The Great Square of Pegasus is tilted over on its lower left corner, and is setting in the north-west, being followed by Andromeda. Triangulum is above the north-north-western horizon. These constellations contain the well-known spiral galaxies M31 (in Andromeda, illustrated at the bottom of this webpage) and M33 (in Triangulum, illustrated below).

The Great Spiral M33 in Triangulum.

The three main stars in Andromeda are, from left to right, Alpheratz, Mirach, and Almach, and above them is the faint constellation of Triangulum, a narrow triangle of stars. M31 lies about eight degrees (one third of a handspan) below and slightly to the left of Mirach tonight. These large spirals are members of the Local Group of galaxies (our Milky Way is a third member), and can be easily seen with binoculars. They are the nearest galaxies that can be observed from the large observatories in the Northern Hemisphere. This month they are best seen as soon as darkness falls, for then they will be closer to due north and therefore at their highest elevation.

Above Triangulum is the zodiacal constellation of Aries, now past the meridian in the north-north- west. There are three main stars in Aries, the brightest being a second magnitude orange star called Hamal. The other two are named Sheratan and Mesarthim . M33 lies midway between Hamal and Mirach.

Cetus, the Whale, lies a little north-west of the zenith. Though this part of the sky has no really bright stars, a little more than a handspan west of the zenith is a mv 2.2 star. This is Beta Ceti, the brightest star in the constellation. Its common name is Diphda, and it has a yellowish-orange colour. By rights, we would expect the star Menkar or Alpha Ceti to be brighter, but Menkar is actually more than half a magnitude fainter than Diphda. Menkar may be seen high in the north-east, halfway between Diphda and Aldebaran.

Cetus is a large constellation, and to the unaided eye it appears unremarkable. But it does contain a most interesting star, which even medieval people noticed. Hevelius named it Mira, the Wonderful (see below). Between Cetus and Pegasus is the zodiacal constellation of Pisces, the Fishes. Pisces is found just to the left of Aries, and this year hosts the planet Uranus.

The spectacular constellations are in the eastern half of the sky tonight. Taurus, with its two star clusters the Pleiades (also known as the Seven Sisters, or Subaru, or Santa's Sleigh) and the Hyades, is high in the north-north-east (see below). The brightest star in Taurus is an orange star dominating the Hyades cluster, but not a member of it. This is Aldebaran, a K5 star with a visual magnitude of 0.87.

Below the Pleiades we can see part of the far-northern constellation of Perseus. The two brightest stars are Mirphak (Alpha Persei) and Algol (Beta Persei). Algol is the higher above the northern horizon of the two. Since ancient times, Algol shows regular variations in brightness. It usually shines at magnitude 2.1, but every 2 days 20 hours 49 minutes it dims to magnitude 3.4 for 10 hours before recovering its original brightness. Because of this clock-like change, early astronomers called it the 'Demon Star'. It marks the head of Medusa, the Gorgon, which is carried in the hand of Perseus.

The Dutch-born Englishman John Goodricke (1764-1786) was a young amateur astronomer. He was profoundly deaf and also dumb after suffering from scarlet fever as an infant. Goodricke is best known for his explanation of the variations in the star Algol (Beta Persei) in 1782. Although several stars were already known to vary in apparent magnitude, Goodricke was the first to propose a mechanism to account for this. He suggested that Algol is actually a pair of stars circling each other, and the variation in brightness is caused when one passes behind the other. Such a star system is now known as an eclipsing binary. He presented his findings to the Royal Society in May 1783, and for this work, the Society awarded him the Copley Medal for that year.

Goodricke is also credited with discovering the periodic variation of the namesake, Delta Cephei, of the type of variable stars called Cepheids, in 1784. It was the second Cepheid found, the first, Eta Aquilae, being found by Goodricke’s friend Edward Pigott earlier the same year. Goodricke proposed that Cepheids were unstable stars that regularly swell up and then fall back - 'pulsating variables' (see Mira, the Wonderful  below).

He was elected a Fellow of the Royal Society on April 16, 1786, but never learned of this honour, as he was very ill and died four days later, probably from pneumonia, aged only twenty-one years and seven months.

Between the Hyades and the north-eastern horizon, the large pentagon of Auriga, the Charioteer has risen. The brightest star in this constellation is Capella, which is directly above the north-north-eastern horizon. Just above Capella is a little triangle of stars, known as 'The Kids'. The top star of Auriga's pentagon, Elnath, points towards Orion. Actually, Elnath is the second-brightest star in Taurus, and forms the tip of one of the Bull's horns.

At 10 pm at the beginning of the month, the two bright stars of Gemini, Castor and Pollux, are just rising above the theoretical north-eastern horizon. These two first magnitude stars are known as 'The Twins'. If your horizon in this direction is very low, you may be able to glimpse them, both stars rising together about five degrees apart. Pollux is the more easterly of the two. If your horizon is not low, you will have to wait a little to see these stars appear. These two stars are the twins' heads, and their feet point towards Orion. Two-thirds of the way from their heads to their feet, each twin is marked by a star at his hip, third magnitude Mebsuta for Castor, and fourth magnitude Mekbuda for Pollux. 

Orion (see below) is about halfway up the sky in the east, and a bright star in Canis Minor (the Lesser Dog), Procyon, is now about half-a-handspan above the eastern horizon. Around midnight at mid-month, Orion will cross the meridian (the north-south line across the sky, passing through the zenith), at which time the constellation is said to ‘culminate’. The three stars marking Orion's Belt will be about twenty-five degrees (a little more than a handspan) north of the zenith. Sirius, the brightest star in the night sky, is south-east of Orion, in the constellation Canis Major (the Greater Dog).

Sirius (Alpha Canis Majoris) is the brightest star in the night sky. It has been known for centuries as the Dog Star. It is a very hot A0 type star, larger than our Sun. It is bright because it is one of our nearest neighbours, being only 8.6 light years away. The four spikes are caused by the secondary mirror supports in the telescope's top end. The faintest stars on this image are of magnitude 15. To reveal the companion Sirius B, which is currently 10.4 arcseconds from its brilliant primary, the photograph below was taken with a magnification of 375x, although the atmospheric seeing conditions were more turbulent. The exposure was much shorter to reduce the overpowering glare from the primary star.

Sirius is a binary, or double star. Whereas Sirius A is a main sequence star like our Sun, only larger, hotter and brighter, its companion Sirius B is very tiny, a white dwarf star nearing the end of its life. Although small, Sirius B is very dense, having a mass about equal to the Sun's packed into a volume about the size of the Earth. In other words, a cubic centimetre of Sirius B would weigh over a tonne. Sirius B was once as bright as Sirius A, but reached the end of its lifespan on the main sequence much earlier, whereupon it swelled into a red giant. Its outer layers were blown away, revealing the incandescent core as a white dwarf. All thermonuclear reactions ended, and no fusion reactions have been taking place on Sirius B for many millions of years. Over time it will radiate its heat away into space, becoming a black dwarf, dead and cold. Sirius B is 63000 times fainter than Sirius A. Sirius B is seen at position angle 62º from Sirius A (roughly east-north-east, north is at the top), in the photograph above which was taken at Nambour on January 31, 2017. That date is exactly 155 years after Alvan Graham Clark discovered Sirius B in 1862 with a brand new 18.5 inch (47 cm) telescope made by his father, which was the largest refractor existing at the time.


Very low in the south, Alpha Crucis (or Acrux), the brightest and most southerly star of Crux (Southern Cross) is beginning to rise. Between Crux and Sirius is a large area of the Milky Way filled with interesting objects. This was once the constellation Argo Navis, named for Jason’s famous ship used by the Argonauts in their search for the Golden Fleece. The constellation Argo was found to be too large, so modern star atlases divide it into three sections - Carina (the Keel), Vela (the Sails) and Puppis (the Stern).

Above the horizon, just to the left of due south and above Acrux, is the small constellation Musca, the Fly. Musca is a circumpolar constellation, i.e. it is always in our sky, being too close to the South Celestial Pole to set. Out of the 88 constellations, it is the only insect.

High in the south-east and two handspans from Sirius is the second brightest star in the night sky, Canopus (Alpha Carinae). On the border of Carina and Vela is the False Cross, larger and more lopsided than the Southern Cross. Both of these Crosses are actually more like kites in shape for, unlike Cygnus (the Northern Cross) they have no star at the intersection of the two cross arms. At the present time, both Crosses are upside-down.

At about thirty-five degrees above the south-western horizon, the flattened triangle of Grus, the Crane, is swinging down. To its right is the bright star Fomalhaut, a bright, white first magnitude star in the faint constellation Piscis Austrinus, the Southern Fish. Fomalhaut means 'the fish's mouth'. A planet revolving around Fomalhaut was recently photographed by the Hubble Space Telescope. Midway between -0.71 magnitude Canopus and 1.16 magnitude Fomalhaut is the 0.46 magnitude star Achernar, in the constellation Eridanus, the River.

Eridanus winds its faint way across the sky from Achernar to Cursa, these two stars marking the ends of the river. Cursa (Beta Eridani) is a 2.79 magnitude star about four degrees to the north-west of Rigel (see below).

To the right of Achernar, the faint constellation of Phoenix may be seen. Its brightest star is Ankaa, a mv 2.39 star which is about one third of the way from Achernar to Diphda. About a handspan south of Achernar is a small, faint glowing patch. This is the Small Magellanic Cloud (SMC). A handspan to its left is a larger glow, the Large Magellanic Cloud (LMC). Both of these glowing clouds are galaxies in their own right, separate from our Milky Way galaxy. They are described in greater detail in Two close galaxies below. The LMC bridges two faint constellations, Dorado and Mensa. The SMC is in the constellation Tucana, the Toucan.

The zodiacal constellations visible tonight, starting from the south-western horizon and heading across to the north-east horizon, are Capricornus, Aquarius, Pisces, Aries, Taurus and Gemini.

If you would like to become familiar with the constellations, we suggest that you access one of the world's best collections of constellation pictures by clicking  here . To see some of the best astrophotographs taken with the giant Anglo-Australian telescope, click here.



The Winged Horse and the Chained Maiden:  

About half-way up the sky from the north-north-western horizon (at the end of twilight on December 1) is a large star group called the Great Square of Pegasus. The Square (actually slightly rectangular) is unusual for the sparcity of bright stars within it. Pegasus was the winged horse of Greek legend, and is used as a symbol by the Mobil Oil Company and TriStar Pictures. By 8.00 pm the Square will be tilted over to the west and it will begin to set in the north-west by 11.00 pm.

The stars making the four corners of the Square, starting from the top left and moving clockwise, are Markab, Algenib, Alpheratz and Scheat. Three of these are in the constellation of Pegasus, but Alpheratz is actually in the constellation Andromeda.

Between Alpheratz and the northern horizon, a very faint glowing oval may be seen if the sky is dark enough. You would need to be away from light pollution caused by bright lights. Binoculars will help you to find it, but it is visible faintly without optical aid. This oval is the Great Nebula in Andromeda (M31), a large spiral galaxy of over 100 million stars. The Andromeda spiral is almost a twin of our own galaxy, the Milky Way. Lying at a distance of 2.6 million light years, it is the furthest object that can be seen with the unaided eye (see The Andromeda Galaxy and the President of the United States  at the bottom of this page).  

The Hunter and his Dogs:

Two of the most spectacular constellations in the sky may be seen rising above the eastern horizon soon after sunset in December. These are Orion the Hunter, and his greater dog, Canis Major. Orion straddles the celestial equator, midway between the south celestial pole and its northern equivalent. This means that the centre of the constellation, the three stars known as Orion's Belt, rise due east and set due west. A smaller constellation, the lesser dog Canis Minor, accompanies them. 


This is one of the most easily recognised constellations, as it really does give a very good impression of a human figure. From the northern hemisphere he appears to stand upright when he is high in the sky, but from our location ‘down under’ he appears lying down when rising and setting, and upside down when high in the sky. You can, though, make him appear upright when high in the sky (near the meridian), by observing him from a reclining chair, with your feet pointing to the south and your head tilted back. 

Orion rising as darkness falls in December

Orion rises south-east of Taurus. If you have a fairly low eastern horizon, you will see most of the constellation rising above the eastern horizon as soon as it gets dark at the beginning of December. The bright Rigel is highest in the sky. The red supergiant Betelgeuse is the last of Orion's bright stars to rise.   

Orion has two bright stars marking his shoulders, the red supergiant Betelgeuse and Bellatrix.

The red supergiant star, Betelgeuse

A little north of a line joining these stars is a tiny triangle of stars marking Orion’s head. In the centre of the constellation are three stars in a line forming Orion's Belt. These are, from west to east, Mintaka, Alnilam and Alnitak. These three stars are related, and all lie at a distance of 1300 light years. They are members of a group of hot blue-white stars called the Orion Association.

To the south of the Belt, at a distance of about one Belt-length, we see another faint group of stars in a line, fainter and closer together than those in the Belt. This is Orion’s Sword. Orion’s legs are marked by brilliant Rigel and fainter Saiph. Both of these stars are also members of the Orion Association.

The Saucepan, with Belt at left, M42 at lower right.

Orion is quite a symmetrical constellation, with the Belt at its centre and the two shoulder stars off to the north and the two leg stars to the south. It is quite a large star group, the Hunter being over twenty degrees (about a handspan) tall. 

The stars forming the Belt and Sword are popularly known in Australia as ‘The Saucepan’, with the Sword forming the Saucepan’s handle. This asterism appears upside-down tonight, as in the photographs above. The faint, fuzzy star in the centre of the Sword, or the Saucepan’s handle, is a great gas cloud or nebula where stars are being created. It is called the ‘Great Nebula in Orion’ or M42*. A photograph of it appears below:  

The Sword of Orion, with the Great Nebula, M42, at centre

The central section of M42, the Great Nebula in Orion.

New stars are forming in the nebula. At the brightest spot is a famous multiple star system, the Trapezium, illustrated below.

Canis Major:

By 8.00 pm in early December, a brilliant white star will be seen rising about one handspan to the south and lower than Orion. This is Sirius, or Alpha Canis Majoris, and it is the brightest star in the night sky with a visual magnitude of -1.43. It marks the heart of the hunter's dog, and has been known for centuries as the Dog Star. As he rises, the dog is on his back with his front foot in the air. The star at the end of this foot is called Mirzam. It is also known as Beta Canis Majoris, which tells us that it is the second-brightest star in the constellation. Mirzam is about one-third of a handspan above Sirius.

The hindquarters of the Dog are indicated by a large right-angled triangle of stars located to the right of Sirius and tilted. The end of his tail is the lower-right corner of the triangle, about one handspan south (to the right) of Sirius. The star at the root of the Dog's tail is called Wezen, and the one at the tip of his tail is called Aludra. The star Adhara marks his back foot. The Dog's head is shown by a faint outline of fourth and fifth magnitude stars.

Both Sirius and Rigel are bright white stars and each has a tiny, faint white dwarf companion. Whereas a small telescope can reveal the companion to Rigel quite easily, the companion to Sirius the Dog Star, (called ‘the Pup’), can only be observed by using a powerful telescope with excellent optics on a night of good 'seeing', as it is very close to brilliant Sirius and is usually lost in the glare.

Canis Major as it appears in the east soon after sunset in December

Canis Minor:

This small constellation contains only two main stars, the brighter of which is Procyon (Alpha Canis Minoris). This yellow-white star of mv= 0.5 forms one corner of a large equilateral triangle, the other two corners being the red Betelgeuse and white Sirius. Beta Canis Minoris is also known as Gomeisa, a blue-white star of mv= 3.1. Procyon rises in the east soon after 9.00 pm at the beginning of December.


Taurus, the Bull:

What is Orion hunting? About a handspan to the left of Orion's Belt is a bright orange star, Aldebaran. It is the brightest star in the constellation Taurus, the Bull. This orange star appears at the foot of a cluster of stars with the appearance of a capital A or inverted V. This cluster is called the Hyades, and seemed to the ancients like the face of a bull, with Aldebaran as his angry orange eye. Being in the southern hemisphere, we see it upside down. Actually, Aldebaran is not physically connected with the Hyades cluster, being much closer, but in the same line of sight.

Half a handspan to the left of the Hyades cluster, and a little higher above the horizon, is another cluster, smaller and fainter. This is the Pleiades, a small group like a question mark. It is often called the Seven Sisters, although excellent eyes are needed to detect the seventh star without binoculars or telescope. The group is also known as ‘Santa’s Sleigh’, as it appears around Christmas time. All the stars in this cluster are hot and blue. They are also the same age, as they formed as a group out of a single gas cloud or nebula. There are actually more than 250 stars in the Pleiades, and this cluster marks the Bull's shoulder.

The Pleiades is the small cluster at centre left, while the Hyades is the much larger grouping at centre right.

Wisps of the nebula which surrounds the Pleiades can be seen around the brighter stars in the cluster.



Mira, the Wonderful:

The amazing thing about the star Mira or Omicron Ceti is that it varies dramatically in brightness, rising to magnitude 2 (brighter than any other star in Cetus), and then dropping to magnitude 10 (requiring a telescope to detect it), over a period of 332 days. 

This drop of eight magnitudes means that its brightness diminishes over a period of five and a half months to one six-hundredth of what it had been, and then over the next five and a half months it regains its original brightness. To the ancients, they saw the familiar star fade away during the year until it disappeared, and then it slowly reappeared again. Its not surprising that Hevelius named it 'Mira', meaning 'The Wonderful' or 'The Miraculous One'.

We now know that many stars vary in brightness, even our Sun doing so to a small degree, with a period of 11 years. One type of star varies, not because it is actually becoming less bright in itself, but because another, fainter star moves around it in an orbit roughly in line with the Earth, and obscures part of it on each pass. This type of star is called an eclipsing variable and they are very common.

The star Mira though, varies its light output because of processes in its interior. It is what is known as a pulsating variable. Stars of the Mira type are giant pulsating red stars that vary between 2.5 and 11 magnitudes in brightness. They have long, regular periods of pulsation which lie in the range from 80 to 1000 days.

This year, Mira reached a maximum brightness of magnitude 3.4 on February 23 and has now dropped well below naked-eye visibility (magnitude 6) again. It reached its minimum brightness of magnitude 9.3 on September 22. This month it will brighten again, reaching its next maximum on January 19, 2018.


Mira near minimum, 26 September 2008                Mira near maximum, 22 December 2008

Astronomers using a NASA space telescope have spotted an amazingly long comet-like tail behind Mira as the star streaks through space. The Galaxy Evolution Explorer - "GALEX" for short - scanned the well-known star during its ongoing survey of the entire sky in ultraviolet light. Astronomers then noticed what looked like a comet with a gargantuan tail. In fact, material blowing off Mira is forming a wake 13 light-years long, or about 20,000 times the average distance of Pluto from the sun. Nothing like this has ever been seen before around a star.   More, including pictures



Double stars:

Estimates vary that between 15% and 50% of stars are single bodies like our Sun, although the latest view is that less than 25% of stars are solitary. At least 30% of stars and possibly as much as 60% of stars are in double systems, where the two stars are gravitationally linked and orbit their mutual centre of gravity. Such double stars are called binaries. The remaining 20%+ of stars are in multiple systems of three stars or more. Binaries and multiple stars are formed when a condensing Bok globule or protostar splits into two or more parts.

Binary stars may
ave similar components (Alpha Centauri A and B are both stars like our Sun), or they may be completely dissimilar, as with Albireo (Beta Cygni, where a bright golden giant star is paired with a smaller bluish main sequence star).


The binary stars Rigil Kentaurus (Foot of the Centaur, or Alpha Centauri) at left, and Beta Cygni (Albireo), at right.


Rigel (Beta Orionis, left) is a binary star which is the seventh brightest star in the night sky.  Rigel A is a large white supergiant which is 500 times brighter than its small companion, Rigel B, yet Rigel B is itself composed or a very close pair of Sun-type stars that orbit each other in less than 10 days. Each of the two stars comprising Rigel B is brighter in absolute terms than Sirius (see above). The Rigel B pair orbit Rigel A at the immense distance of 2200 Astronomical Units, equal to 12 light-days. (An Astronomical Unit or AU is the distance from the Earth to the Sun.)  In the centre of the Great Nebula in Orion (M42) is a multiple star known as the Trapezium (right). This star system has four bright white stars, two of which are binary stars with fainter red companions, giving a total of six. The hazy background is caused by the cloud of fluorescing hydrogen comprising the nebula.

Acrux, the brightest star in the Southern Cross, is also known as Alpha Crucis.  It is a close binary, circled by a third dwarf companion.

Alpha Centauri
(also known as Rigil Kentaurus, Rigil Kent or Toliman) is a binary easily seen with the smallest telescope. The components are both solar-type main sequence stars, one of type G and the other, slightly cooler and fainter, of type K. Through a small telescope this star system looks like a pair of distant but bright car headlights. Alpha Centauri A and B take 80 years to complete an orbit, but a tiny third component, the 11th magnitude red dwarf Proxima takes about 1 million years to orbit the other two. It is about one tenth of a light year from the bright pair and a little closer to us, hence its name. This makes it our nearest interstellar neighbour, with a distance of 4.3 light years. Red dwarfs are by far the most common type of star, but, being so small and faint, none is visible to the unaided eye. Because they use up so little of their energy, they are also the longest-lived of stars. The bigger a star is, the faster it burns its nuclear fuel and the shorter its life.

Close-up of the star field around Proxima Centauri

Knowing the orbital period of the two brightest stars A and B, we can apply Kepler’s Third Law to find the distance they are apart. This tells us that Alpha Centauri A and B are about 2700 million kilometres apart or about 2.5 light hours. This makes them a little less than the distance apart of the Sun and Uranus (the orbital period of Uranus is 84 years, that of Alpha Centauri A and B is 80 years.)

Albireo (Beta Cygni) is sometimes described poetically as a large topaz with a small blue sapphire. It is one of the sky’s most beautiful objects. The stars are of classes G and B, making a wonderful colour contrast. It lies at a distance of 410 light years, 95 times further away  than Alpha Centauri.

Binary stars may be widely spaced, as the two examples just mentioned, or so close that a telescope is struggling to separated them (Acrux, Castor, Antares, Sirius). Even closer double stars cannot be split by the telescope, but the spectroscope can disclose their true nature by revealing clues in the absorption lines in their spectra. These examples are called spectroscopic binaries. In a binary system, closer stars will have shorter periods for the stars to complete an orbit. Eta Cassiopeiae takes 480 years for the stars to circle each other. The binary with the shortest period is AM Canum Venaticorum, which takes only 17½ minutes.

Sometimes one star in a binary system will pass in front of the other one, partially blocking off its light. The total light output of the pair will be seen to vary, as regular as clockwork. These are called eclipsing binaries, and are a type of variable star, although the stars themselves usually do not vary.



Why are some constellations bright, while others are faint ?

The Milky Way is a barred spiral galaxy some 100000 – 120000 light-years in diameter which contains 100 – 400 billion stars. It may contain at least as many planets as well. Our galaxy is shaped like a flattened disc with a central bulge. The Solar System is located within the disc, about 27000 light-years from the Galactic Centre, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. When we look along the plane of the galaxy, either in towards the centre or out towards the edge, we are looking along the disc through the teeming hordes of stars, clusters, dust clouds and nebulae. In the sky, the galactic plane gives the appearance which we call the Milky Way, a brighter band of light crossing the sky. This part of the sky is very interesting to observe with binoculars or telescope. The brightest and most spectacular constellations, such as Crux, Canis Major, Orion and Scorpius are located close to the Milky Way.

If we look at ninety degrees to the plane, either straight up and out of the galaxy or straight down, we are looking through comparatively few stars and gas clouds and so can see out into deep space. These are the directions of the north and south galactic poles, and because we have a clear view in these directions to distant galaxies, these parts of the sky are called the intergalactic windows. The southern window is in the constellation Sculptor, not far from the star Fomalhaut. This window is well-placed for viewing this month, and many distant galaxies can be observed in this area of the sky. The northern window is between the constellations Virgo and Coma Berenices, roughly between the stars Denebola and Arcturus. It is below the horizon in the evenings this month.

Some of the fainter and apparently insignificant constellations are found around these windows, and their lack of bright stars, clusters and gas clouds presents us with the opportunity to look across the millions of light years of space to thousands of distant galaxies.



Some fainter constellations:

Between the two Dogs is the constellation Monoceros the Unicorn, undistinguished except for the presence of the remarkable Rosette Nebula. South of Orion is a small constellation, Lepus the Hare. Between Lepus and the star Canopus is the star group Columba the Dove.  Between the zenith and the south-western horizon are a number of small, faint constellations, Phoenix, Hydrus, Reticulum, Indus and Pavo. Clustered around the South Celestial Pole are Dorado, Octans, Apus, Chamaeleon, Mensa and Volans.



Finding the South Celestial Pole:

The South Celestial Pole is that point in the southern sky around which the stars rotate in a clockwise direction. The Earth's axis is aimed exactly at this point. For an equatorially-mounted telescope, the polar axis of the mounting also needs to be aligned exactly to this point in the sky for accurate tracking to take place.

To find this point, first locate the Southern Cross. Project a line from the orange star at the top of the Cross (Gacrux) to the star at its base (Acrux) and continue straight on towards the south (to the left) for another four Cross lengths. This will locate the approximate spot. There is no bright star to mark the Pole, whereas in the northern hemisphere they have Polaris (the Pole Star) to mark fairly closely the North Celestial Pole.

Another way to locate the South Celestial Pole is to draw an imaginary straight line joining Beta Centauri in the south-west to Achernar in the south-east. Bisect this imaginary line to locate the pole.

Neither of these methods will work in Queensland during December evenings as both the Southern Cross and Beta Centauri are below the horizon. However, they will have risen by 1 am.

Interesting photographs of this area can be taken by using a camera on time exposure. Set the camera on a tripod pointing due south, and open the shutter for thirty minutes or more. The stars will seem to move during the exposure, being recorded on the film as short arcs of a circle. The arcs will be different colours, as the stars are. All the arcs will have a common centre of curvature, which is the south celestial pole.

   A wide-angle view of trails around the South Celestial Pole, with Scorpius and Sagittarius at left, Crux and Centaurus at top, and Carina and False Cross at right.

Star trails between the South Celestial Pole and the southern horizon. All stars that do not pass below the horizon are circumpolar.


Star Clusters:

The two clusters in Taurus, the Pleiades and the Hyades, are known as Open Clusters or Galactic Clusters. The name 'open cluster' refers to the fact that the stars in the cluster are grouped together, but not as tightly as in globular clusters (see below). The stars appear to be loosely arranged, and this is partly due to the fact that the cluster is relatively close to us, i.e. within our galaxy, hence the alternate name, 'galactic cluster'. These clusters are generally formed from the condensation of gas in a nebula into stars, and some are relatively young.

The photograph below shows a typical open cluster, M7*. It lies in the constellation Scorpius, just above the scorpion's sting. It lies in the direction of our galaxy's centre. The cluster itself is the group of white stars in the centre of the field. Its distance is about 380 parsecs or 1240 light years. M7 is not visible tonight.

Galactic Cluster M7 in Scorpius

Outside the plane of our galaxy, there is a halo of Globular Clusters. These are very old, dense clusters, containing perhaps several hundred thousand stars. These stars are closer to each other than is usual, and because of its great distance from us, a globular cluster gives the impression of a solid mass of faint stars. Many other galaxies also have a halo of globular clusters circling around them.

The largest and brightest globular cluster in the sky is NGC 5139**, also known as Omega Centauri. It has a slightly oval shape. It is an outstanding winter object, but this month it is below the horizon for much of the night. Shining at fourth magnitude, it is faintly visible to the unaided eye, but is easily seen with binoculars, like a light in a fog. A telescope of 20 cm aperture or better will reveal its true nature, with hundreds of faint stars giving the impression of diamond dust on a black satin background. It lies at a distance of 5 kiloparsecs, or 16 300 light years.

The globular cluster Omega Centauri

The central core of Omega Centauri

Although Omega Centauri is below the horizon in the evenings this month, there is another remarkable globular, second only to Omega, which is in a good position. Close to the SMC (see Two close galaxies below), binoculars can detect a fuzzy star. A telescope will reveal this faint glow as a magnificent globular cluster, lying at a distance of 5.8 kiloparsecs. Its light has taken almost 19 000 years to reach us. This is NGC 104, commonly known as 47 Tucanae. Some regard this cluster as being more spectacular than Omega Centauri, as it is more compact, and the faint stars twinkling in its core are very beautiful. This month, 47 Tucanae is best placed for viewing at 8 pm.

The globular cluster 47 Tucanae

Observers aiming their telescopes towards the SMC generally also look at the nearby 47 Tucanae, but there is another globular cluster nearby which is also worth a visit. This is NGC 362, which is less than half as bright as the other globular, but this is because it is more than twice as far away. Its distance is 12.6 kiloparsecs or 41 000 light years, so it is about one-fifth of the way from our galaxy to the SMC. Both NGC 104 and NGC 362 are always above the horizon for all parts of Australia south of the Tropic of Capricorn.

The globular cluster NGC 6752 in the constellation Pavo.


*     M7:  This number means that this galactic cluster in Scorpius is No. 7 in a list of 103 astronomical objects compiled and published in 1784 by Charles Messier. Charles was interested in the discovery of new comets, and his aim was to provide a list for observers of fuzzy nebulae and clusters which could easily be reported as comets by mistake. Messier's search for comets is now just a footnote to history, but his list of 103 objects is well known to all astronomers today, and has even been extended to 110 objects.

**    NGC 5139:  This number means that Omega Centauri is No. 5139 in the New General Catalogue of Non-stellar Astronomical Objects. This catalogue was first published in 1888 by J. L. E. Dreyer under the auspices of the Royal Astronomical Society, as his New General Catalogue of Nebulae and Clusters of Stars. As larger telescopes built early in the 20th century discovered fainter objects in space, and also dark, obscuring nebulae and dust clouds, the NGC was supplemented with the addition of the Index Catalogue (IC). Many non-stellar objects in the sky have therefore NGC numbers or IC numbers. For example, the famous Horsehead Nebula in Orion is catalogued as IC 434. The NGC was revised in 1973, and lists 7840 objects. 

The recent explosion of discovery in astronomy has meant that more and more catalogues are being produced, but they tend to specialise in particular types of objects, rather than being all-encompassing, as the NGC / IC try to be. Some examples are the Planetary Nebulae Catalogue (PK) which lists 1455 nebulae, the Washington Catalogue of Double Stars (WDS) which lists 12 000 binaries, the General Catalogue of Variable Stars (GCVS) which lists 28 000 variables, and the Principal Galaxy Catalogue (PGC) which lists 73 000 galaxies. The largest modern catalogue is the Hubble Guide Star Catalogue (GSC) which was assembled to support the Hubble Space Telescope's need for guide stars when photographing sky objects. The GSC contains nearly 19 million stars brighter than magnitude 15.



Two close galaxies:

At 10 pm on December 1, two faint smudges of light may be seen high in the south. These are the two Clouds of Magellan, known to astronomers as the LMC (Large Magellanic Cloud) and the SMC (Small Magellanic Cloud). The LMC is to the left of the SMC, and is noticeably larger. They lie at distances of 190 000 light years for the LMC, and 200 000 light years for the SMC. They are about 60 000 light years apart. These dwarf galaxies circle our own much larger galaxy, the Milky Way. The LMC is slightly closer, but this does not account for its larger appearance. It really is larger than the SMC, and has developed as an under-sized barred spiral galaxy.

The Large Magellanic Cloud - the bright knot of gas to left of centre is the famous Tarantula Nebula (below)

These two Clouds are the closest galaxies to our own, but lie too far south to be seen by the large telescopes in Hawaii, California and Arizona. They are 15 times closer than the famous Andromeda and Triangulum galaxies in the northern half of the sky, and so can be observed in much clearer detail. Our great observatories in Australia, both radio and optical, have for many years been engaged in important research involving these, our nearest inter-galactic neighbours. 



The Andromeda Galaxy and the President of the United States:

In 1901, U.S.A. President William McKinley was assassinated and his Vice-President,
Theodore Roosevelt, took his place. Theodore became a popular President, and was elected in his own right in 1904 for a second term. He was known as Teddy Roosevelt, and the Teddy Bear is named after him. As President he was a dynamic, vigorous and energetic man, very keen on preserving the wonders of nature through the creation of national parks, forests, and natural monuments such as Rainbow Bridge. 

Teddy made the acquaintance of noted American naturalist, scientist, explorer and author William Beebe who shared his love of nature. They became friends and would meet regularly for dinner and an evening's conversation, sometimes with friends of similar interests. Both men had strong egos, but recognised the dangers of pride in themselves and in their accomplishments. 

It is said that after dinner, Roosevelt, Beebe and their friends would step outside for cigars and lengthy discussions about world affairs. At the conclusion, they would look up at the starry sky. Roosevelt or Beebe would point out a small, faint smudge of light close to the Great Square of Pegasus and they would both recite, almost as a litany, something similar to the following:

"That is the Spiral Galaxy in Andromeda. It is as large as our Milky Way. It is one of a hundred million galaxies. It consists of one hundred million suns, many larger than our sun." The President would then turn to the others. "Now I think we are small enough," he would say. "Let's go to bed."

Whereas from the latitude of Washington D.C. the Andromeda Galaxy is visible for most of the year, from Australia it is so far north (41 degrees north declination) that it is only visible in the evenings during spring and early summer. For us, this magnificent galaxy is due north at 8 pm on December 1, about one handspan above the horizon.

The Great Galaxy in Andromeda, M31, photographed at Starfield Observatory with an off-the-shelf digital camera on 16 November 2007.

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