November 2017

Updated:   22 November 2017

 

 

Welcome to the night skies of Spring, featuring Saturn, Scorpius, Sagittarius, Aquila, Lyra and Cygnus 

 

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 constellation of Libra, the Scales. It leaves Libra and passes across an outstretched claw of Scorpius, the Scorpion between November 23 and 30. On November 30, the Sun moves into the non-zodiacal constellation of Ophiuchus, the Serpent Bearer.   

 

 

Moon Phases:  Lunations (Brown series):  #1174, 1175 

 

Full Moon:                November 04             15:23 hrs          diameter = 32.8'
Last Quarter:           November 11             06:37 hrs          diameter = 31.9' 
New Moon:               November 18            21:42 hrs          diameter = 29.7'
First Quarter:           November 27             03:03 hrs          diameter = 30.4'

Full Moon:                December 04            01:47 hrs           diameter = 33.4'   
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' 

 

 

       

Lunar Orbital Elements:



November 06:         Moon at perigee (361 431 km) at 10:03 hrs, diameter = 33.1'
November 11        Moon at ascending node at 08:44 hrs, diameter = 31.8'
November 22:         Moon at apogee (406 112 km) at 04:28 hrs, diameter = 29.4'

November 25
:         Moon at descending node at 18:22 hrs, diameter = 29.9'

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'


 

Moon at 8 days after New, as on November 28.

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 one of the most spectacular ranges of mountains on the Moon, the Montes Apenninus, and the crater Eratosthenes which is at the range's western end.

 

Sunrise on the Apennines: the crater Eratosthenes and the Montes Apenninus on the Moon, photographed from Nambour on August 1, 2017.


The Montes Apenninus or Apennine Mountains is a range of peaks in the Moon's northern hemisphere at about latitude 20º North. It forms a gentle curve on the south-east margin of Mare Imbrium (Sea of Rains), and is just a few kilometres short of being 1000 km long. Some of the peaks reach up 5.4 kilometres above their bases on the lava plain to the north. The Jesuit priest who named most of the features on the Moon, Riccioli, named the range "Terra Nivium" (Land of Snows), and the picture above shows that at lunar sunrise the peaks can have the appearance of being snow-capped.

A contemporaneous observer, Johannes Hevelius, had already named this line of mountains after the Apennine Range in Italy, and an adjoining range to the north after the Alps. Although the Alps are not shown in the image above, they can be seen in  the photograph below. Hevelius in fact named all the most prominent lunar features after well-known places on the Earth. For example, on his maps of the Moon you will find the Mediterranean Sea with the islands of Sicily, Sardinia, Corsica and Majorca, and a large crater (Copernicus) named Mt Etna. People thought that this was a confusing idea and his system of names failed to win popularity. When Riccioli produced his new nomenclature a few years later, in which craters were named after famous and historic people, the names given by Hevelius were superseded by Riccioli's. But these two ranges were exceptions - later observers preferred to keep the Moon's Alps and Apennines.

Both of those ranges form the eastern rim of Mare Imbrium, a great circular 'sea' on the Moon - although it looks oval from Earth - that was caused by the tremendous impact of a large asteroid (see below).

The Imbrium Event

The Moon and planets coalesced out of debris in the solar nebula about 4.6 billion years ago. Most of the craters on the Moon were formed early, during the next 500 million years. At that time, there was a lot of material in orbit around the Sun, and the planets attracted much of it to themselves. There were major collisions of asteroid-sized rocks with all the inner planets, and they still show the scars. Earth, despite the effects of weather and erosion, still has some large impact craters or astroblemes, two in Australia being Wolfe Creek Crater and Gosse’s Bluff.

After the main bombardment had ended, most of the Moon was covered in craters overlapping each other. The south polar region of the Moon and the far side still have this appearance. Some large asteroids were still in unstable orbits, and a number of them collided with the near side of the Moon, obliterating the older features and releasing huge amounts of molten lava from the interior to spread out over the surface and create the great lava plains now known as 'maria' or 'seas'. These lava plains are visible to the unaided eye as the dark patches on the Moon, particularly in the northern hemisphere, that people refer to as the "Man in the Moon". All of the maria are the results of these huge impacts.

The final one of these impacts was created by a huge asteroid about 3.85 billion years ago. We don’t know its size, but it was probably half as big as Tasmania, and it struck the northern hemisphere of the Moon. This impact is known as the Imbrium Event. The kinetic energy of the asteroid, travelling at between 20 and 25 km per second, was instantaneously converted into heat energy as the asteroid was stopped dead on impact. This heat energy vaporised much of the asteroid, liquified more of it into "rock melt", and created a stupendous explosion that sent liquified rock and solid chunks of debris hurtling across the lunar surface, causing severe damage that is readily visible today with a small telescope, and known as "Imbrium sculpture".

The explosion blasted out a crater over 1100 kilometres across and possibly 100 km deep. Its area ia about the size of New South Wales. A powerful pulse of energy went vertically down into the Moon, where it hit bedrock and bounced straight back, shattering and lifting the floor of the new crater which was by now only a few seconds old. The floor was lifted so that the crater ended up being only about 12 km deep with a heavily fractured floor. Superheated rock from the Moon's mantle, kept solid by the pressure of overlying rocks before the impact, immediately liquefied as the fractures above released the pressure. This liquefied rock, called magma, immediately rose from the Moon’s mantle through the fractures in the crust and flooded across the surface, swamping the destroyed area with great lava flows which filled the floor of the great crater, rendering it more-or-less flat and featureless

The circular area resulting from this cataclysm is known to us today as Mare Imbrium, the Sea of Rains. It is outlined by white dots in the photograph below. The area is circled by great mountain ranges, including the Alps and the Apennines, which are in fact the original ramparts of the crater. Protruding from the lava floor of Mare Imbrium are isolated mountain peaks, such as Mons Pico and Mons Piton. Their bases are way below the mare surface. As different flows of lava occurred, waves in the surface were caused, which hardened as they cooled and are visible today as wrinkle ridges. Some craters were formed after the initial lava flows had solidified, and then partially or completely flooded by later flows. These are called ghost craters.  

When the initial Imbrium Event occurred, large blocks of rock the size of mountains were sent crashing for hundreds of kilometres across the lunar surface, particularly heading south-south-east. These caused lines of secondary impact craters and great longitudinal scars to be formed as the blocks bounced along, all radiating from the centre of the Imbrium Event impact site. Most are seen in the area north and north-east of the crater Ptolemæus in the centre of the Moon's disc.

Since those times, new craters have been formed on or close to what was once the level, smooth Mare Imbrium. Eratosthenes is one of them. Probably the best known is Copernicus, a 95 km wide perfect example of an impact crater. Its walls have huge terraces where the surface has slumped down, and it is over 3 km deep. In the centre there is the typical cluster of mountains, resulting from the rebound of deep rock strata after the impact. It was created by a much smaller impact than the Imbrium Event. Copernicus is indicated on the photograph below between two short dark blue lines.

The rectangle shows the location of the crater Eratosthenes and the Apennine Mountains. The white dots show the extent of Mare Imbrium.


Eratosthenes

Eratosthenes (ca. 276-194 BCE, left), was a custodian of the Great Library in Alexandria, at the mouth of the Nile. Many of our Greek myths about the constellations come to us through his writings and those of Hyginus. The story goes that Eratosthenes was told by a visitor that at noon on the summer solstice (June 21), the Sun shone vertically down a well further up the Nile River at Syene, its reflection appearing in the water. Also, vertical sticks and tall columns were seen to ‘swallow their shadows’ around the time of the summer solstice. He checked this the following year and found that it was so, and that, at the same time on the same day, the Sun was 7.2º from the vertical at Alexandria.

Knowing the distance between the two observing sites to be 5000 stadia, about 800 kilometres, a stade or stadion being 157.5 metres (he hired professional ‘steppers’ to pace it out using a standard stride), he used this information to make a famous measurement of the diameter and circumference of the Earth, getting quite an accurate result. His method was simple: the 7.2º angle between the two towns is about 1/50 of a circle of 360º. This distance equals 800 kilometres.

It is also possible that, rather than having been told about a well by a visitor, Eratosthenes had read the old Egyptian data (then more than 2000 years old) that the Sun did not cast any shadows at noon on the summer solstice at obelisks on Elephantine, an island in the Nile adjacent to Syene. His calculation of the Earth’s circumference turned out to be very close to the true figure of 40 025 km (polar circumference), but it seems that he had more than his share of good fortune. The fact that Syene is slightly north of the Tropic of Cancer should have made the Sun shine down the well at a slight angle, not vertically. We are not told how deep the well was, and if it was exactly vertical. Would the use of their primitive measuring instruments at Alexandria have provided the quoted accuracy? How accurate were the measurements of the man or men who paced the distance? All of these factors would have introduced small errors into his observations and calculations, but luckily they appear to have cancelled each other out. In any case, he was the first man to measure the size of a planet, and all he used was sticks, eyes, feet and brains.

Eratosthenes is credited with the invention of the armillary sphere. Although not the first Greek to do so, he measured the obliquity of the ecliptic (its inclination to the equator) and realised that this figure indicated the amount of tilt of the Earth’s axis. His result of 23½º was only 7 arcminutes from the correct figure. He drew a map of the Hellenistic world for use by navigators. It was later used as a basis for a map by Claudius Ptolemy in his Almagest , and was not superseded until the great voyages of discovery at the end of the fifteenth century.


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.

 

November 1:         Jupiter 1.9º south of the star Kappa Virginis (mv= 4.18) at 14:26 hrs
November 3:         Moon 3.7º south of Uranus at 12:14 hrs
November 6:         Limb of Moon 41 arcminutes north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 12:43 hrs
November 7:         Moon 1.6º south of the star Zeta Tauri (mv= 2.97) at 13:05 hrs
November 8:         Mercury 1.8 arcminutes south of the star Delta Scorpii (mv= 2.29) at 03:56 hrs
November 11:       Mercury 1.8º north of the star Sigma Scorpii (mv= 2.90) at 21:47 hrs
November 12:       Moon 1.1º north of the star Regulus (Alpha Leonis, mv= 1.36) at 01:48 hrs
November 13:       Jupiter 31 arcminutes north of the star Lambda Virginis (mv= 4.51) at 02:17 hrs
November 13:       Mercury 2.2º north of the star Antares (Alpha Scorpii, mv= 1.06) at 05:47 hrs
November 13:       Venus 15.7 arcminutes north of Jupiter at 18:12 hrs
November 15:       Moon 3.1º north of Mars at 14:49 hrs
November 17:       Moon 4.2º north of Jupiter at 10:09 hrs
November 17:       Moon 4.1º north of Venus at 19:46 hrs
November 18:       Saturn 44.7 arcminutes south of the star 58 Ophiuchi (mv= 4.86) at 23:58 hrs
November 20:       Venus 46.6 arcminutes north of the star Zuben Elgenubi (Alpha Librae, mv= 2.75) at 03:17 hrs
November 20:       Moon 7.3º north of Mercury at 22:04 hrs
November 21:       Moon 3.3º north of Saturn at 08:57 hrs
November 22:       Neptune at eastern stationary point at 21:27 hrs  (diameter = 2.3")
November 23:       Moon 1.8º north of the star Pi Sagittarii (mv= 2.88) at 02:43 hrs
November 23:       Moon 2.6º north of Pluto at 04:21 hrs
November 24:       Mercury at greatest elongation east (21º 52') at 12"23 hrs  (diameter = 6.6")
November 27:       Limb of Moon 44 arcminutes south of Neptune at 14:38 hrs
November 28:       Mercury 3.1º south of Saturn at 19:38 hrs
November 30:       Moon 3.4º south of Uranus at 22:33 hrs


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



 

The Planets for this month

  

Mercury:    On November 1, Mercury will be in the evening sky, being just above the Sun at sunset, but difficult to find due to its proximity to the solar glare. By the second week of November Mercury will be increasing its angular separation from the Sun, but it will not become an easy object until the second half of the month. On November 20 and 21, there will be a grouping of Mercury, Saturn and the thin crescent Moon just above the western horizon soon after sunset. On November 28, Mercury will be only 3 degrees south of Saturn.

 

Venus:  This, the brightest planet, is still to be found in the pre-dawn sky as a 'morning star', although its angular distance from the Sun continues to diminish day by day. For example, on November 1 Venus will be 17 degrees from the Sun (about a handspan), and by November 30 its elongation will have fallen to 10 degrees, making it hard to find due to the brightness of the dawn sky. This process will continue as speeding Venus curves around towards the far side of the Sun. Venus will pass behind the Sun (superior conjunction) on January 9 next year. After that, Venus will return to the western sky as an 'evening star'. In early November, Venus will appear in a small telescope as a tiny 'Full Moon' with a magnitude of -3.9 and an angular size of 10 arcseconds. Its phase will be 98%. As the month progresses, Venus will become difficult to locate without telescopic aid.

(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.

Having passed through conjunction with the Sun on July 27, the red planet is becoming easier to observe this month. On November 1 it will be nearly two handspans from the Sun, in the constellation Virgo. 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. 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.

In mid-November Mars will rise at about 3 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 November 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, and will become visible in the second-half of November as a pre-dawn object.


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 visible in the evenings this month, being about two-and-a-half handspans above the western horizon as darkness falls, 7 pm. The waxing crescent Moon will be close by Saturn on November 21. 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 s hines 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 almost Full Moon will be in the vicinity of Uranus on November 3 and 30.

Neptune:   The icy blue planet is an evening object this month. It reached opposition on September 5, and in mid-November it is about a handspan north of the zenith at 7 pm. 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


Pluto
: 
 The erstwhile ninth and most distant planet can be observed in the early evenings this month, as it reached opposition on July 10, when it rose at sunset. Pluto's angular diameter is 0.13 arcseconds, less than one twentieth that of Neptune. This month it is within 1.7 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.

 

Meteor Showers:

 

S Taurids                 November 3 and 4                    Almost Full Moon, 98% sunlit                                         ZHR = 15
                                 Radiant: Near the Pleiades star cluster.    Associated with Comet Encke

N Taurids                 November 13 and 14                Waning crescent Moon, 26% sunlit                                ZHR = 15
                                 Radiant:  Near the Pleiades star cluster.    Associated with Comet Encke 

   
Leonids                    November 18 and 19                New Moon, 1% sunlit                                                      ZHR = 12
                                 Radiant: Near the third magnitude star Adhafera, in the Lion's mane.    Associated with Comet Tempel-Tuttle


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.

 

 

 

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 h as faded below magnitude 18.

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 November 1 and 8 pm on November 30. Broadly speaking, the following description starts low in the south-west and follows the horizon to the right, heading round to the east, then south, then overhead.

 

The stars of Sagittarius are setting low in the west-south-west. Just above them, the faint stars of Capricornus will soon be gone, too. Above Capricornus is another rather faint constellation, Aquarius, the Water Bearer. There are no stars brighter than third magnitude in this constellation, but it does contain many interesting objects, including a group of four stars known as the 'Water Jar'. Also, this year faint Neptune may be found in its centre, about a handspan east of the star Deneb Algedi.

The Lagoon Nebula, M8, in Sagittarius, adjacent to Scorpius

The centre of the Lagoon Nebula

The first magnitude star Altair (Alpha Aquilae) can be seen approaching the horizon a little north of west. Altair is the brightest star in the constellation Aquila, the Eagle. It has a fainter star above and another below, making a vertical line of three, quite close together. These stars, from top to bottom, are AlshainAltair and Tarazed, and they indicate the Eagle's body. A handspan east of the bright, first magnitude Altair is a faint but easily recognised diamond-shaped group of stars, Delphinus the Dolphin. The Great Square of Pegasus is beginning to tilt over towards the north-west, and Andromeda and Triangulum are above the northern horizon.

The names of the four stars marking the corners of the Square (starting at the top-left one and moving in a clockwise direction around the Square) are Markab, Algenib, Alpheratz and Scheat. Although these four stars are known as the Great Square of Pegasus, only three are actually in the constellation of Pegasus, the Winged Horse. In point of fact, Alpheratz is the brightest star of the constellation Andromeda, the Chained Maiden. This is the best time of year to observe two close spiral galaxies, for they are due north and at their highest elevation. M31 (in Andromeda) and M33 (in Triangulum) are members of the Local Group of galaxies (our Milky Way is a third member), and can be easily seen with good binoculars. They are the nearest galaxies that can be observed from the large observatories in the Northern Hemisphere.

Andromeda trails down from Alpheratz to below the north-eastern horizon. To its right is the zodiacal constellation of Aries, now well up in the north-east. The brightest star in Aries is a second magnitude orange star called Hamal.  Between Aries and Aquarius is a faint constellation, Pisces, the Fishes. A well-known asterism in Pisces is the Circlet, a faint circle of seven fourth and fifth magnitude stars. About one and a third handspans east of the Circlet may be found the planet Uranus, but it is not visible without at least a pair of binoculars.

Taurus, with its two star clusters the Pleiades and the Hyades, is well above the north-eastern horizon, below Aries. The Pleiades is a small group like a question mark, and is often called the Seven Sisters, although excellent eyes are needed to detect the seventh star without optical aid. 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 gas cloud or nebula. There are actually more than 250 stars in the Pleiades. The Japanese name for this cluster is 'Subaru', and the cars of that make have a representation of the cluster as their badge.

The Hyades cluster appears larger, with the appearance of a capital A or inverted V. At the foot of its right leg is a bright orange star called Aldebaran (Alpha Tauri). The V shape looked 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. The Pleiades form 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 gas can be seen around the brighter stars in the Pleiades cluster.

Orion the Hunter is rising in the east, and to its right is his Great Dog (Canis Major), marked by the brilliant white star Sirius (the Dog Star), quite close to the horizon. Sirius is the brightest star in the night sky, because it is one of our closest neighbours, only 8.6 light-years away. The second-brightest star in the night sky is Canopus, which is two handspans to the right of Sirius, high in the south-east. It is bright, not because it is close, (as it is at a distance of 312 light-years, 36 times further away than Sirius), but because it is in fact a supergiant star. About one handspan south-east of the zenith is a bright first-magnitude white star, Achernar (Alpha Eridani). Achernar, the ninth brightest star, is at one end of a very long, faint constellation, Eridanus, the River. It winds all the way from Achernar to Cursa (Beta Eridani), a 2.9 magnitude star just above Rigel, the brightest star in Orion (see below).

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.


Achernar is midway between two other bright stars, Canopus and Fomalhaut. The latter is a handspan south-west of the zenith. Slightly north of the zenith is a mv 2.2 star. This is Beta Ceti, the brightest ordinary star in the constellation Cetus, the Whale. Its common name is Diphda, and it has a yellowish-orange colour. By rights, the star Menkar or Alpha Ceti should 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.

Above Diphda is Fomalhaut, a bright, white first magnitude star in the faint constellation Piscis Austrinus, the Southern Fish. Fomalhaut is almost directly overhead at 8 pm on November 1. South-west of Fomalhaut is a large, upside-down flattened triangle of stars, Grus, the Crane. North of Achernar, the faint constellation of Phoenix may be seen. Its brightest star is Ankaa, a mv 2.39 star which is halfway between Fomalhaut and Achernar.

Cetus is a large constellation, and to the unaided eye it appears unremarkable. But it does contain a most interesting star, which was discovered before the telescope was invented. It is named Mira, the Wonderful (see below). Between Cetus and Pegasus is the zodiacal constellation of Pisces, the Fishes. Pisces is found just above Aries. Moving westwards from Cetus we see the zodiacal constellations of Aquarius, then Capricornus.

Rising in the south-east are the stars of the constellation Carina, and the False Cross. The true Southern Cross (Crux) is below the southern horizon, but will rise soon after midnight.  Above the horizon due south, is the small constellation of 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. Alpha Centauri is close to the horizon nearby.

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

 

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 3.9 metre Anglo-Australian Telescope near Coonabarabran, NSW
 

 

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. The seventeenth century Polish astronomer Johannes 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 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. The next maximum will occur on January 19, 2018.

    

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


Astronomers using a NASA space telescope, the Galaxy Evolution Explorer, have spotted an amazingly long comet-like tail behind Mira as the star streaks through space. 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 and multiple 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 have 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 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 small telescope is struggling to separate them (Acrux, Castor, Antares, Sirius). Even closer double stars cannot be split by even large telescope, buts 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.

 

 

 

The Milky Way



A glowing band of light crossing the sky is especially noticeable during the winter months, but it is far less noticeable this month, virtually skirting the horizon at 9 pm. This glow is the light of millions of faint stars combined with that coming from glowing gas clouds called nebulae. It is concentrated along the plane of our galaxy, and at the beginning of November it can be seen at 7:30 pm running from south-south-west to north-north-west, reaching a maximum elevation above the horizon of about two handspans, due west.  Constellations in the Milky Way at this time tonight will run from Centaurus through  Scorpius, Sagittarius and Aquila to Cygnus.

The plane of our galaxy from Scutum (at left) through Sagittarius and Scorpius (centre) to Centaurus and Crux (right). The Eta Carinae nebula is at the right margin, below centre.
The Coalsack is clearly visible, and the dark dust lanes can be seen. Taken with an ultra-wide-angle lens.

It is rewarding to scan along this band with a pair of binoculars, looking for star clusters and emission nebulae. Dust lanes along the plane of the Milky Way appear to split it in two in some parts of the sky. One of these lanes can be easily seen, starting near Alpha Centauri and heading towards Antares.

The centre of our galaxy. The constellations partly visible here are Sagittarius (left), Ophiuchus (above centre) and Scorpius (at right). The planet Jupiter is the bright object below centre left. This is a normal unaided-eye view.

 

 

 

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 method is much use on November evenings as the Cross is below our southern horizon until after midnight.

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.

Galactic Cluster M7 in Scorpius, known as Ptolemy's cluster

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, in some cases . 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 most 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 poorly placed for viewing this month, there is another remarkable globular, second only to Omega, which is in a good position. Close to the SMC (see 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, Omega Centauri is not at a good position for viewing, but 47 Tucanae is well placed before midnight.

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 Ptolemy's 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


Above the south-south-eastern horizon, two faint smudges of light may be seen. 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 below 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 LMC is less than a handspan above the horizon, and the SMC is a little more than a handspan above and slightly to the right of the LMC.

 

 

 

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 8:50 pm in mid-November, 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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