February  2018

Updated:   8 February 2018

 

Welcome to the night skies of Summer, featuring Auriga, Taurus, Gemini, Orion, Canis Major and Carina

 

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 with fingers spread 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 middle of the constellation of Capricornus, the Sea-Goat. It leaves Capricornus and passes into Aquarius, the Water-Bearer on February 16.   

 

 

Partial Solar Eclipse, February 16:

There will be a partial solar eclipse occurring on February 16 next (Australian Eastern Standard Time). No part of the eclipse will be visible from Australia. The only continents that will be in the eclipse path will be Antarctica and the southern part of South America. Countries south of Brazil will still be in the afternoon of February 15 when the eclipse occurs.

 


Moon Phases:
 
Lunations (Brown series):  #1176, 1177, 1178 

 

Full Moon:                January 31               23:27 hrs          diameter = 33.2'      Total lunar eclipse
Last Quarter:           February 08             01:55 hrs          diameter = 30.1' 
New Moon:               February 16             07:06 hrs          diameter = 30.0'      Partial solar eclipse  (not visible from Queensland).  
     Lunation #1177 begins
First Quarter:           February 23             18:09 hrs          diameter = 32.0'

Full Moon:                March 02                  10:52 hrs          diameter = 32.5'     
Last Quarter:           March 09                  21:21 hrs          diameter = 29.7' 
New Moon:               March
17                  23:12 hrs          diameter = 30.8'     Lunation #1178 begins
First Quarter:           
March 25                  01:36 hrs          diameter = 32.3'
Full Moon:               
March 31                  22:38 hrs          diameter = 31.6'     


 
 

Lunar Orbital Elements:



February 12:         Moon at apogee (405 713 km) at 00:25 hrs, diameter = 29.5'
February 15:         Moon at descending node at 07:08 hrs, diameter = 29.8'

February 28:         Moon at perigee (363 913 km) at 00:50 hrs, diameter = 32.8'
February 28:         Moon at ascending node at 15:02 hrs, diameter = 32.8'

March 11:             Moon at apogee (404 694 km) at 19:16 hrs, diameter = 29.5'
March 14            Moon at descending node at 13:44 hrs, diameter = 29.8'
March 27:             Moon at perigee (369 114 km) at 03:11 hrs, diameter = 32.4'
March 27:             Moon at ascending node at 20:56 hrs, diameter = 32.4'
 

Moon at 8 days after New, as on February 24.

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 the spectacular crater, Tycho.

 

This photograph of Tycho and its environs was taken on August 2, 2017. South is to the top and east is to the left.

 

Tycho is probably the youngest large impact crater on the Moon. Its diameter is 88 km and it lies at the centre of a spectacular system of light-coloured rays. These rays stretch in some cases for thousands of kilometres across the lunar surface, and are best seen at Full Moon. They are caused by rocks and boulders the size of city blocks bouncing across the Moon's surface after the initial impact and blast. As they strike the surface, which has been darkened by solar radiation, they gouge furrows and craterlets in it which reveal the lighter material underneath. This lighter material is splashed out along the trajectories of the bouncing boulders, creating the light-coloured rays. Tycho's surroundings are covered with areas of rock melt, some of which are peppered with large angular blocks. Much of the crater floor shows evidence of the internal upheaval which lifted the central mountain complex. This mountain has three peaks and is 1.5 km high.
 

Tycho

Between 1580 and 1700, the notion that transparent, solid, crystalline spheres surrounding the Earth were a physical reality gradually lost ground, and was largely abandoned by the time of Newton's death in 1727. In the 1580s and 1590s, this was mainly due to the influence of a Dane, Tycho Brahe (1546-1601, pronounced ‘Twee-co Brar-hee’, right), who was the greatest and most accurate observer of the pre-telescopic era, and a worthy successor to Copernicus. Tycho was first-born into a noble family in the Danish province of Scania (now at the southern tip of Sweden), but when he was quite young, a second sibling was born. His father Otto permitted Tycho to be adopted by his childless Uncle Jørgen and his wife, a move designed to elevate the boy's ranking in the nobility. Later, In a drunken incident, Jørgen rescued the King of Denmark Frederik II from drowning, but himself caught pneumonia and died. From then on, the King always considered himself as being responsible for the young lad's welfare as his folly had deprived the boy of his benefactor. This royal interest had important implications for Tycho's future.

Becoming interested in astronomy as a teenager after seeing a solar eclipse in 1560, Tycho soon found that existing planetary tables were very imprecise. Resolving to remedy this, he built an observatory equipped with quality instruments near his home at Herrevads Abbey in Scania. In 1572 Tycho made an astronomical observation from this observatory that was to change his life. He was well aware of the positions of many stars, but on November 11 he saw a ‘new star’ in the constellation of Cassiopeia, which at its peak was even visible by day and outshone Venus for some weeks. In fact, he was not the first person to see it, but because he studied it in detail, it will always be remembered as ‘Tycho’s Star’.

According to the Ptolemaic theory of cosmology, changes in the sky (such as comets, meteors and clouds) could only occur between the sphere of the Moon and the Earth. Tycho proved that the new star did not change its position against the background stars if charted simultaneously by two observers at different, widely spaced locations, whereas the Moon did. In other words, the new star showed no parallax as the Moon does, so it had to be further away than the Moon. The appearance of the new star (actually, a very old star exploding in its death throes) therefore contradicted the accepted view that the universe from the sphere of the Moon up was unchanging. In the light of this, Tycho began to question the whole validity of the geocentric theories of Ptolemy and Aristotle, and investigated the new Copernican heliocentric theory that had first appeared 30 years earlier. Thrilled by his discovery, Tycho rushed into print with a book describing the phenomenon, De Nova Stella (On the New Star). The book was published within a few months of the discovery, in 1573.

Tycho’s book made his reputation and he moved to Copenhagen in 1574. He was already well known to the Danish royal family, but the new discovery brought generous royal patronage. King Frederik II granted him the small, nearby island of Hven and enough funds to build a three-storey manor surrounded by small elevated observatories. He named it ‘Uraniborg (The Castle of Urania – the Muse of Astronomers)’ and determined to make it a world-famous centre of astronomy. 

With the number of visiting astronomers rapidly growing as Uraniborg’s fame spread, the manor soon proved to be inadequate. Also, the outlying observing platforms, some held up by a single pillar, proved to be unstable and prone to deflection by the wind and the movements of observers. Tycho therefore decided to remove his instruments from the elevated platforms and place them at ground level or below ground. He built a new observatory across the road from Uraniborg, and called it ‘Stjerneborg (Castle of the Stars)’. Above the entrance was the motto: “Neither high office nor wealth, only the power of art [science] endures.”

Solid granite formed the foundations and the instruments were mounted on short granite pillars. The smaller instruments were protected by low enclosures with roofs of a much lower profile than those used across the road. Hatches were used which opened the enclosures to the heavens. The work rooms and sleeping quarters were underground. The largest instrument was covered by a large dome, which could be smoothly rotated in any direction. These ideas became the models for other European observatories, as the visiting astronomers carried them back to their homelands.

Tycho rejected all previous observations as dubious, and aimed to ‘reconstruct astronomy’ by personally surveying all heavenly phenomena from scratch. Unlike many other observers, Tycho measured the positions of stars and planets, not just near opposition, but along their whole orbits right around the heavens, to the limit of naked-eye precision. His measurements of the positions of stars and planets were of unprecedented accuracy, being within 2 arcminutes of the correct values. He measured the length of the year to within one second of the modern value. He worked at Uraniborg for 17 years. Among Tycho Brahe’s many results was his proof that a comet was a heavenly body and not an atmospheric phenomenon as some had previously assumed. In addition, he discovered two hitherto unknown anomalies in the movements of the Moon. To assist with his planetary work, by 1592 Tycho had completed a catalogue with the positions and magnitudes of 777 fixed stars. This was the first new star catalogue known in the Latin West since the time of Ptolemy.   

Tycho studied the Earth-centred universe of Ptolemy and the Sun-centred universe of Copernicus, but could not fully accept either of them. Instead, he devised a third version of the universe, which he claimed embodied the best features of the other two, without their problems. In Tycho's universe, the five planets Mercury, Venus, Mars, Jupiter and Saturn all circled on their transparent spheres around the Sun, but the Sun and Moon both circled around the Earth on their spheres. The Earth, as in Ptolemy's universe, lay fixed and unmoving at the centre of everything.

The "Tychonic Universe" is seen at right. As Tycho knew that Mars came closer to the Earth than the Sun did, its sphere needed to cross inside that of the Sun for part of its orbit. This meant that the spheres could not be solid, as many believed. He proposed that they were made of a "fluid medium" (an amorphous version of Plato's æther or quintessence).

King Frederik II died in 1588 and his 11-year-old son became King Christiaan IV. The boy King's councillors made life difficult for Tycho, cutting his funding and then his pension. He packed up his instruments and left Denmark in disgust, never to return. He found work at the court of the Holy Roman Emperor Kaiser Rudolph II in Prague, as Imperial Mathematician, and began producing a new, up-to-date almanac to be called the Rudolphine Tables. He enlisted a young Johannes Kepler to assist.

The work had barely started when Tycho died unexpectedly after attending a banquet on October 24, 1601. He was only 54 and had been in good health, so the circumstances of his death have always been suspect. Kepler took his post of Imperial Mathematician, and completed the Rudolphine Tables in 1627, using Tycho's data. In doing this work, Kepler discovered his Three Laws of planetary motion.

Tycho is regarded as the greatest naked-eye observer. It is a great shame that he did not live into old age, as only eight years after his early death the first telescopes appeared and were turned to the sky, proving that the Copernican version of the universe was more accurate than either the Ptolemaeic or the Tychonic.


 
The crater Tycho is shown by the yellow rectangle.



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.

 

February 1:          Mars 22 arcminutes south of the star Graffias (Beta Scorpii, mv= 2.56) at 12:59 hrs
February 2:          Moon 1.1º north of the star Regulus (Alpha Leonis, mv= 1.36) at 05:10 hrs
February 6:          Venus 1.2º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 07:25 hrs
February 8:          Moon 4.2º north of Jupiter at 09:29 hrs
February 9:          Moon 4.8º north of Mars at 17:48 hrs
February 11:        Jupiter at western quadrature at 09:08 hrs
February 11:        Moon 4.2º north of of Saturn at 23:16 hrs
February 12:        Moon 1.7º north of the star Pi Sagittarii (mv= 2.88) at 21:40 hrs
February 13:        Moon 2.1º north of Pluto at 03:37 hrs
February 15:        Mercury 32 arcminutes north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 03:26 hrs
February 15:        Saturn 1.9º south of the star 21 Sagittarii (mv= 4.8) at 12:29 hrs
February 16:        Moon 2.4º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 12:03 hrs
February 16:        Moon 1.5º north of Mercury at 02:33 hrs
February 17:        Moon occults Venus between 01:21 and 02:05 hrs
February 17:        Moon 1.2º south of Neptune at 15:01 hrs
February 17:        Mercury in superior conjunction at 22:11 hrs (diameter = 4.9")
February 20:        Moon 3.7º south of Uranus at 20:17 hrs
February 21:        Neptune (mv= 8.0) 1 arcminute south of the star SAO 146431 (mv= 8.98) at 18:34 hrs (both will set at 19:01 hrs)
February 22:        Venus 32 arcminutes south of Neptune at 04:53 hrs
February 24:        Moon 1.3º north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 03:12 hrs
February 25:        Moon 1.6º south of the star Zeta Tauri (mv= 2.97) at 05:26 hrs
February 25:        Mercury 26 arcminutes south of Neptune at 22:37 hrs

March 1:             Moon 1.4º north of the star Regulus (Alpha Leonis, mv= 1.36) at 15:10 hrs
March 4:             Neptune in conjunction with the Sun at 23:58 hrs (diameter = 2.2")
March 5:             Mercury 1.1º north of Venus at 03:14 hrs
March 7:             Moon 4.7º north of Jupiter at 18:31 hrs
March 9:             Jupiter at western stationary point at 13:21 hrs (diameter = 40.0")
March 10:           Moon 4.1º north of Mars at 12:49 hrs
March 10:           Mercury at perihelion at 20:57 hrs (diameter = 6.4") 
March 11:           Moon 2.6º north of Saturn at 13:38 hrs
March 12:           Limb of Moon 57 arcminutes north of the star Pi Sagittarii (mv= 2.88) at 03:49 hrs
March 12:           Moon 2.3º north of Pluto at 15:34 hrs
March 15:           Moon 1.8º north of the star Deneb Algedi (Alpha Capricorni, mv= 2.85) at 06:42 hrs
March 15:           Mercury at Greatest Elongation East (18º 17') at 20:15 hrs (diameter = 7.3")
March 16:           Moon 1.1º south of Neptune at 23:18 hrs
March 19:           Moon 3.4º south of Venus at 06:08 hrs
March 19:           Moon 7.1º south of Mercury at 08:03 hrs
March 19:           Mercury 3.9º north of Venus at 12:56 hrs
March 20:           Moon 4.2º south of Uranus at 04:19 hrs
March 21:           Autumn Equinox at 02:15 hrs
March 23:           Limb of Moon 43 arcminutes north of the star Aldebaran (Alpha Tauri, mv= 0.87) at 07:36 hrs
March 23:           Mercury at eastern stationary point at 10:12 hrs (diameter = 9.3")
March 24:           Moon 1.5º south of the star Zeta Tauri (mv= 2.97) at 09:05 hrs
March 25:           Mars at western quadrature at 01:52 hrs (diameter = 8.0")
March 29:           Limb of Moon 58 arcminutes north of the star Regulus (Alpha Leonis, mv= 1.36) at 02:23 hrs
March 29:           Venus 4 arcminutes south of Uranus at 10:43 hrs
March 29:           Mars 1.9º north of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82) at 19:41 hrs
March 30:           Saturn at western quadrature at 00:11 hrs (diameter = 16.5")

 


The Planets for this month:
   

 

Mercury:   Mercury overtook the Earth, passing between us and the Sun on December 13. In January, Mercury was in the morning sky, and will still be there on February 1. It will pass on the far side of the Sun on February 17, and will then return to the evening twilight sky, being above the Sun at sunset but hard to find due to the solar glare. It will become noticeable in the west soon after sundown in early March, and will be at its maximum distance from the Sun (18º 17') on March 15, and quite easy to observe. The thin crescent Moon will be 7.1º to the left of Mercury on March 19.

 

Venus:  This, the brightest planet, passed through superior conjunction (on the far side of the Sun) on January 9. It is still so close to the Sun that it is swamped by the glare. No attempt should be made to observe it unless special solar filters are employed. However, while a telescope may reveal Venus, 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.  Venus has now returned to the western twilight sky as an 'evening star', and will move away from the solar glare next month. By mid-March, Venus will be about a handspan east of the Sun, and will appear in a small telescope as a tiny 'Full Moon' with a magnitude of -3.9 and a phase of 96%.

(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).

                           February 2018                            August 2018                       September 2018                      

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 passed on the far side of the Sun (superior conjunction) on January 9, 2018, and has now returned to the evening sky to 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.

 

This is the year of Mars:   Having passed through conjunction with the Sun on July 27, the red planet is becoming easier to observe this month. On February 1 it will be a midnight object, rising at 25 minutes after midnight in an outstretched claw of the constellation Scorpius. On that date it will shine at magnitude 1.2, will have a diameter of 6 arcseconds, and be very close to the bright star Acrab in the head of the Scorpion. On February 8, Mars will move east into the constellation Ophiuchus, the Serpent bearer. As the Earth catches up to Mars, the red planet will brighten and appear a little larger each night.

This planet was named 'Mars' by the Romans, and 'Ares' by the Greeks, both after the god of War, because its orange-red colour was similar to that of blood. The brightest star in Scorpius (Alpha Scorpii) was named 'Antares' by the Greeks (meaning 'rival of Ares' or rival of Mars), for it was also orange-red in colour and sometimes was a similar brightness to that of Mars. In such cases, if the planet and the star were together in the sky, one might be mistaken for the other. This was not a common occurrence, as Mars varies greatly in brightness, whereas the star Antares shines quite steadily at magnitude 1.06.

However, it will happen this month. Mars and Antares will be together in the sky in the early morning hours of February 13, and unusually they will both be at about the same brightness. They will be 5.1 degrees apart, a little more than the distance between Alpha and Beta Centauri, the two Pointers to the Southern Cross. Check them out to see if Antares is really a good 'rival of Mars'. 

As the Earth catches up to Mars, the red planet will continue to brighten and appear a little larger each night. By the end of February, Mars will be in the centre of Ophiuchus, It will have brightened to magnitude 0.8 and will have a diameter of 7 arcseconds. On March 11, Mars will cross into Sagittarius, the Archer.

The change its its appearance will be slow at first, but during next June and July Mars will become markedly bigger and brighter from week to week, so that at opposition on July 27 it will be nearly twice as bright as Jupiter.

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. The next time that Mars will reach a size at opposition as favourable as this coming July will be in September 2035, when Mars will be in the constellation Aquarius.

On February 9 the waning crescent Moon will be just to the left (north) of Mars, with Jupiter above it.

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:   This gas giant planet is now visible in the early morning sky, in the constellation Libra, the Scales. It begins the month below the star Zuben Elgenubi, which is the brightest star in Libra. Mars is closer to the horizon. At mid-month Jupiter will rise in the east-south-east at about 11 pm. The Last Quarter Moon will rise a little to the left (north) of Jupiter just before midnight on February 7. Jupiter reached western quadrature (rising at midnight) on February 11, and will reach opposition on May 9.


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 was in conjunction with the Sun on December 22, and in mid-February rises a little after 2 am. It begins February in the constellation Sagittarius, near the magnitude 2.82 star Kaus Borealis. It will remain in this vicinity all year. The waning crescent Moon will be to the left of Saturn in the early hours of February 11 and 12. Saturn will reach western quadrature (rising at midnight) on March 30, and will reach opposition on June 27. Saturn will be near the Trifid Nebula (M 20) and the Lagoon nebula (M 8) in September.

 

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.
The dark hexagonal atmospheric feature located at Saturn's North Pole is visible.

 

Uranus:  This ice giant planet is badly placed for viewing this month, as it is heading towards conjunction with the Sun on April 18. On February 1 it will be a little more than a handspan above the west-north-western horizon as darkness falls. 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 crescent Moon will be just to the left of Uranus on February 20.

 

Neptune:   The icy blue planet cannot be easily observed this month, as it will be in conjunction with the Sun on March 4. On February 1 it will be only 30 degrees east of the Sun in the western twilight sky, and on February 28 it will be only 4 degrees east of the Sun - impossible to observe. At 7 pm on February 17, the thin crescent Moon will be 2 degrees above Neptune, but both will be very close to the horizon.

Neptune, photographed from Nambour on October 31, 2008


Pluto
: 
 The erstwhile ninth and most distant planet is a pre-dawn object this month, as it was in conjunction with the Sun on January 9. By the end of February, Pluto will rise at about 2 am in the east-south-east. 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.
A telescope with an aperture of 25 cm or more is necessary to observe Pluto.

 

  

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:

Alpha Centaurids            February 8                      Last Quarter Moon, 49% sunlit                         ZHR = 10
                                        Radiant:  Near the star Alpha Centauri.


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 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.

In February the Eta Carinae Nebula is quite low in the south-east soon after sunset. By 9 pm it is directly above the Southern Cross, and it is at its highest above the horizon at 1 am.

 

 

 

The Stars and Constellations for this month:

 

This description of the night sky is for 9 pm on February 1 and 7 pm on February 28. They start at Orion, which is very high, a handspan north of the zenith.

 

This month, the constellation of Orion (see below) is as high as he can ever appear from our latitude. He is about 25 degrees north of the zenith, and has just crossed the meridian (the line that runs from due south to due north and passing through the zenith, directly overhead). When a sky object crosses the meridian, it is said to be culminating. At that point, it ceases rising and begins setting. Orion will have set by 3.00 am.

The bright orange-red star Betelgeuse (Alpha Orionis) will culminate at 9 pm on February 2. The brilliant white star Rigel (Beta Orionis), twice as bright as Betelgeuse, is at this time half a handspan past the meridian. About a hand-span to the south-east of Rigel is the brightest star in the night sky, Sirius, also known as Alpha Canis Majoris. Sirius is almost directly overhead at 9.00 pm at mid-month. At the zenith itself is a faint constellation, Columba, the Dove.

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 six times as much magnification, although the atmospheric seeing conditions in the current heatwave 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.

 

The constellation Taurus, the Bull, with the clusters the Pleiades and Hyades is between Orion and the north-western horizon. The brightest star in Taurus is a star dominating (but not actually a member of) the Hyades cluster. This is Aldebaran, a K5 orange star with a visual magnitude of 0.87. 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 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.

 

Setting in the west are the constellations Cetus, Pisces and Aries, none of which is spectacular. Low in the north-west, the three main stars of Aries (from the left, Gamma, Beta and Alpha Arietis, otherwise known as Mesarthim, Sheratan and Hamal), form a short bent line parallel with the horizon.  One reasonably bright star, Diphda (Alpha Ceti) is low in the west, and another, Fomalhaut, is near the south-western horizon. By midnight the Pleiades will have disappeared, and the rest of Taurus follows them below the horizon soon after.

Between Orion’s head and the northern horizon is a large constellation shaped roughly like a pentagon. This is Auriga the Charioteer, its brightest star being Capella, at the left side of the base of the pentagon. Capella is the sixth brightest star in the sky, after Sirius, Canopus, Alpha Centauri, Beta Centauri and Vega. Above Capella and slightly to the left is a small triangle of stars known as 'The Kids'. The lower star in this triangle is Epsilon Aurigae, one of the largest stars known. It is also very distant. West of Auriga, the constellation Perseus is straddling the north-north-western horizon.

The top star of Auriga's pentagon is actually in the constellation Taurus. It is El Nath, also known as Beta Tauri. It marks the tip of one of the Bull's horns.

To the east of Auriga, Gemini is quite high, the two twin stars at its eastern end, Pollux and Castor being a little more than a handspan above the north-north-east horizon. East of Gemini is a faint zodiacal constellation, Cancer, the Crab. Though it has no bright stars, Cancer does contain a rich open cluster of stars, known as the Praesepe or the Beehive Cluster. Praesepe was known in antiquity, and is a wonderful sight in binoculars or a small telescope.

A handspan due east of Betelgeuse in Orion (see below) is Procyon, the brightest star in the small constellation of Canis Minor, the Lesser Dog. Procyon is midway between the bright stars Rigel and Regulus.

Rising in the north-east is another zodiacal constellation, Leo, the Lion. The bright star Regulus (Alpha Leonis) marks the Lion’s heart. Leo is fully risen by 10.00 pm, the star marking the tip of the lion's tail, Denebola, being the last star in Leo to rise.

Just beginning to appear above the east-south-eastern horizon is the constellation Corvus the Crow, shaped like a quadrilateral of magnitude 3 stars. A large but faint constellation, Hydra, winds its way from near Procyon around the eastern horizon and over the top of Corvus to Libra, which will not rise until 11:30 pm at mid-month. Hydra has one bright star, Alphard, mv=2.2, which tonight is about one-and-a-half handspans above the eastern horizon. Alphard is an orange star that was known by Arabs in ancient times as ‘The Solitary One’, as it lies in an area of sky with no bright stars nearby.

Well up in the south-south-east, Crux (Southern Cross) is sloping, but will be almost horizontal by 10 pm at mid-month. Crux will have rotated clockwise to a vertical position by 3.15 am at mid-month. Surrounding Crux on three sides is the large constellation Centaurus, and below Crux and to the right are two brilliant stars, Rigil Kentaurus and Hadar. They are also known as Alpha and Beta Centauri. Beta is the one nearer to Crux. These two stars are also known as the Pointers or the Guardians of the Cross.

Crux is at centre, lying horizontally. Beneath Crux lies the Coalsack. Towards the bottom are the two Pointers, Alpha and Beta Centauri. At top centre, the Eta Carinae nebula, also shown below.

 

Above and to the right of Crux is a small, fainter quadrilateral of stars, Musca, the Fly. Out of all the 88 constellations, it is the only insect. To the right of Alpha Centauri and below Musca is a (roughly) equilateral triangle of 4th magnitude stars. This is the constellation Triangulum Australe, the Southern Triangle. It is very low on the horizon, just east of south.

Between Crux and Sirius is a very large area of sky filled with interesting objects. This was once the constellation Argo Navis, named for Jason’s famous ship used by the Argonauts in their quest 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).

A handspan south of the zenith and two handspans south of 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. The False Cross is two handspans above Crux, and is also lying on its side at this time of year. It is high in the south-south-east. 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.

About midway between Crux and the False Cross is a faintly glowing patch, easily seen with the naked-eye and a splendid view in binoculars or a small telescope. This is the famous Eta Carinae Nebula, a vast panorama of hydrogen gas being made to fluoresce or glow because of the intense radiation being emitted by the eruptive variable star at its centre, Eta Carinae itself.

The central part of the Eta Carinae nebula, showing dark lanes, molecular clouds, and glowing clouds of fluorescing hydrogen

The Keyhole, a dark cloud obscuring part of the Eta Carinae Nebula

The Homunculus, a tiny planetary nebula ejected by the eruptive variable star, Eta Carinae

 

Two beautiful star clusters are in the same part of the sky, one on either side of Eta Carinae. The most southerly in the cluster IC 2602, also called the 'Southern Pleiades'. The other is NGC 3532, the 'Firefly Cluster', a more distant but very rich cluster. All three objects can be seen together when viewed through binoculars.

The cluster IC 2602, known as the 'Southern Pleiades'.

 The 'Wishing Well Cluster', NGC 3532.

 

Two handspans south-west of Canopus is Achernar, Alpha Eridani. It is the brightest star in Eridanus the River and marks its mouth. Eridanus has its source at Cursa, a mv= 2.9 star close to brilliant Rigel in Orion, and then winds its way with faint stars in a southerly direction to Achernar.  Achernar curves down towards the south-south-westerly horizon during the evening, and has set by 2 am.

High in the south, about 50 degrees above the horizon, the Large Magellanic Cloud (LMC) is faintly visible as a diffuse glowing patch. To its right and below is the Small Magellanic Cloud (SMC), a smaller glowing patch. The LMC and SMC are described below.

The zodiacal constellations visible tonight, starting from the western horizon and heading to the right between one and two handspans above the horizon until the due east point is reached, are Pisces, Aries, Taurus, Gemini, Cancer and Leo.

 

 

The season of the Hunter and his Dogs:


Two of the most spectacular constellations in the sky may be seen high in the east as soon as darkness falls. These are Orion the Hunter, and his large 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. 

Orion:

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 has two bright stars marking his shoulders, the red supergiant Betelgeuse and Bellatrix. A little north of a line joining these stars is a tiny triangle of stars marking Orion’s head. The three stars forming his Belt 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.

The red supergiant star, Betelgeuse

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 the Sword of Orion. Orion’s two feet are marked by brilliant Rigel and fainter Saiph. Both of these stars are also members of the Orion Association.

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

Orion is quite a symmetrical constellation, with the Belt at its centre and the two shoulder stars off to the north and the two knee stars to the south. It is quite a large star group, the Hunter being over twenty degrees (a little more than 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’ (number 42 in Messier’s list of clusters and nebulae). 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:

To the right of Orion as twilight ends (facing east), a brilliant white star will be seen about one handspan away. 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 neck 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. The end of his tail is the lower-right corner of the triangle, about one handspan south (to the right) of Sirius.

Both Sirius and Rigel are bright white stars and each has a tiny, faint 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, as it is very close to brilliant Sirius and is usually lost in the glare (see above)..

Canis Major as it appears almost overhead at 9 pm at mid-month (observer facing west).

 

Canis Minor:

By 8 pm at mid-month, this small constellation is about 50 degrees above the north-eastern horizon. It 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.

 


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. Eridanus the River winds its way from near Orion west of the zenith to Achernar, high in the south-west. Between Achernar and the western horizon is the star Fomalhaut, a white star of first magnitude in the small constellation of Piscis Austrinus (the Southern Fish). To the left of Fomalhaut is the triangular constellation of Grus, the Crane. Between the zenith and the south-western horizon are a number of small, faint constellations:  Horologium, Pictor, Caelum, Mensa, Tucana, Phoenix, Hydrus and Reticulum. The LMC lies in the constellation Dorado, and the South Celestial Pole is in the very faint constellation of Octans.

 


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 top of the Cross (the star Gacrux) through its base (the star Acrux) and continue straight on towards the south 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 (low in the south-south-east) to Achernar (low in the south-west). Both stars will be about a handspan above the horizon at 9:50 pm at mid-month, and a line joining them will be horizontal. Bisect this line to find the pole.

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 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.

 

 

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 many 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.

      

The binary stars Rigil Kentaurus (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) 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 Centauri, 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.

Alpha Centauri, with Proxima

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 (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.

 

 

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 below 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

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 is close to the horizon in summer. 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

There is another remarkable globular, second only to Omega Centauri. About two degrees below 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, 47 Tucanae is low in the south-south-west, and not clearly visible. By 10 pm Omega Centauri is high enough for detailed viewing.

Globular Cluster NGC104 in Tucana

The globular cluster NGC 6752 in the constellation Pavo.

 

*     M42:  This number means that the Great Nebula in Orion is No. 42 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:

High in the south, to the left of Achernar, two large 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 to the left and above the SMC, and is noticeably larger. They lie at a distance of 160 000 light years, and are about 60 000 light years apart. They are dwarf galaxies, and they 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.

From our latitude both Magellanic Clouds are circumpolar. This means that they are closer to the South Celestial Pole than that Pole's altitude above the horizon, so they never dip below the horizon. They never rise nor set, but are always in our sky. Of course, they are not visible in daylight, but they are there, all the same.

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 referred to above, 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. 

 

 

Why are some constellations bright, while others are faint ?

Our galaxy is shaped like a flattened disc containing about 100 million stars. Our own star, the Sun, with its Solar System is located about two-thirds of the distance out from the centre. 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 low in the south-west in the early evenings this month, but sets by 11 pm. 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 early evenings this month, but rises in the east-north-east at about 10 pm.

 

 

Astronomy Picture of the Day

Click here to access a new spectacular picture every day - this link will also provide you with access to a wonderful library of astronomical photographs from telescopes, spacecraft and manned lunar missions.

 

Virtual Moon freeware

Study the Moon in close-up, spin it around to see the far side, find the names and physical attributes of craters, seas, ranges and other features, by clicking  here.

 

 

Calsky software

Check out where the planets and their moons are, as well as most other sky objects, by clicking  here.


 

 

Stellarium freeware

New version. Check out where the stars and constellations are, as well as most other sky objects, by clicking  here.

 

 

Observatory Home Page and Index