March  2010

Updated:   1 March 2010
Welcome to the night skies of Autumn, featuring  Orion, Canis Major, Gemini and Leo

  

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. Queensland does not observe daylight saving time. Observers in other time zones will need to make their own corrections where appropriate. With conjunctions of the Moon and planets, 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. 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 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 magnitude 15. 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 Sun magnitude -27. 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).

 

  

Solar System

 

Sun:  The Sun begins the month in the constellation of Aquarius, the Water-bearer. It passes into Pisces, the Fishes on March 12.

 

Moon Phases:   Lunations this month:  #1078, 1079 

Full Moon:             March 1                          2:38 hrs            diameter = 33.3'
Last Quarter:        March 8                          1:43 hrs            diameter = 30.3'
New Moon:            March 16                        7:02 hrs            diameter = 29.8'
First Quarter:        March 23                      21:00 hrs            diameter = 31.9'
Full Moon:             March 30                      12:26 hrs            diameter = 32.8'

Last Quarter:        April 6                           19:38 hrs            diameter = 29.8'
New Moon:            April 14                         22:29 hrs            diameter = 30.4'
First Quarter:        April 22                           4:20 hrs            diameter = 32.2'
Full Moon:             April 28                         22:19 hrs            diameter = 31.9'

Note:  In March there are two Full Moons in the same month. This phenomenon occurs about once every three years, although this year is unusual in that January also had two Full Moons. Popular usage calls the extra Full Moon a 'blue Moon', but its colour remains the same as usual. The true description of a 'blue Moon' is actually more complicated. Click here for more information from Wikipedia.

Lunar Orbital Elements:

March 10:              Moon at ascending node at 18:06 hrs, diameter = 29.6' 
March 12:              Moon at apogee (406 014 km) at 20:03 hrs, diameter = 29.4' 
March 24:              Moon at descending node at 23:03 hrs, diameter = 32.3' 
 March 28:              Moon at perigee (361 871 km) at 14:51 hrs, diameter = 33.0'

April 6:                   Moon at ascending node at 19:45 hrs, diameter = 29.8' 
April 9:                   Moon at apogee (405 008 km) at 12:44 hrs, diameter = 29.5' 
April 20:                 Moon at descending node at 23:34 hrs, diameter = 32.0' 
April 25:                 Moon at perigee (367 148 km) at 7:04 hrs, diameter = 32.5'        
 

Moon at 8 days after New, as on March 24

Moon at 9 days after New, as on March 25

The two photographs above show the Mare Imbrium area in the Moon's northern hemisphere. They were taken a day apart, just after First Quarter. Mare Imbrium (the Sea of Rains) is a large lava flow caused by the Imbrium Event - a cataclysmic collision of an asteroid with the Moon many millions of years ago. A comparison of the two photographs will show how the appearance of lunar features changes with the angle of the Sun. 

In the first photograph, Mare Imbrium (left) is separated from Mare Serenitatis (right) by two ranges of mountains, the Alps to the north and the Apennines to the south. Two large craters at upper right are Aristoteles and Eudoxus. The straight Alpine Valley may be seen cutting through the Alps. Mt Piton (height 2000 metres) is visible as a bright spot with a shadow, due south of the southern end of the Alpine Valley. Archimedes is the large crater at left. It is a walled plain 80 kilometres in diameter with a flat floor. To its right are two bowl-shaped craters, Aristillus and Autolycus.  These craters are all formed by impact with large meteors. Apollo 15 landed close by the Apennines, in a small enclosed area to the right and below Archimedes, on the picture's central vertical axis.

In the second photograph, the sunrise line (called the 'terminator') has moved to the left, revealing a large walled plain in the Alps, known as Plato. South of Plato, an isolated mountain protruding through the lava flow is called Mt Pico. Ripples in the lava, called 'wrinkle ridges', are visible. The crater at lower left is Timocharis, 42 kilometres in diameter.

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, 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 !

 

Geocentric Events:

March 2:           Moon 7.5º south of Saturn at 19:21 hrs
March 4:           Venus 37 arcminutes south of Uranus at 14:11 hrs
March 4:           Venus 44 arcseconds north of the star SAO 146915 (mv= 5.5) at 22:56 hrs
March 6:           Moon 1.1º south of the star Dschubba (Delta Scorpii, mv= 2.29) at 22:49 hrs
March 6:           Moon 2.3º north of the star Pi Scorpii (mv = 2.89) at 22:55 hrs
March 7:           Moon 32 arcminutes north of the star Sigma Scorpii (mv= 2.9) at 8:18 hrs
March 7:           Moon 1.7º north of the star Antares (Alpha Scorpii, mv = 1.06) at 12:02 hrs
March 8:           Mercury 1.1º south of Jupiter at 12:12 hrs
March 9:           Moon 5.9º south of Pluto at 14:27 hrs
March 9:           Moon 1.6º north of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82) at 15:55 hrs
March 10:         Moon 1.2º south of the star Pi Sagittarii (mv= 2.88) at 12:29 hrs
March 11:         Mars at eastern stationary point at 2:07 hrs
March 13:         Moon 4º north of Neptune at 22:32 hrs
March 14:         Mercury in superior conjunction at 23:11 hrs
March 15:         Moon 5.1º north of Jupiter at 6:41 hrs
March 17:         Moon 6.7º north of Venus at 15:59 hrs
March 17:         Uranus in conjunction with the Sun at 16:52 hrs
March 21:         Autumn Equinox at 3:25 hrs
March 21:         Moon occults stars in the Pleiades star cluster between 7:30 and 10:30 hrs (not visible from Australia)
March 22:         Saturn at opposition at 10:25 hrs
March 24:         Moon 2º north of the star Mu Geminorum (mv= 2.87) at 2:11 hrs
March 24:         Moon 3º south of the star Mebsuta (Epsilon Geminorum, mv= 3.06)   at 9:38 hrs
March 25:         Moon 3.8º south of Mars at 21:36 hrs
March 26:         Pluto at western quadrature at 13:24 hrs
March 29:         Mercury at perihelion at 21:14 hrs
March 30:         Moon 8º south of Saturn at 5:05 hrs
March 31:         Mars at aphelion at 9:25 hrs
 

April 3:              Moon 1.6º north of the star Sigma Scorpii (mv= 2.9) at 17:12 hrs
April 3:              Moon  2.2º north of the star Antares (Alpha Scorpii, mv = 1.06) at 20:49 hrs
April 5:              Moon 5.6º south of Pluto at 22:35 hrs
April 5:              Moon 1.6º north of the star Kaus Borealis (Lambda Sagittarii, mv= 2.82) at 23:20 hrs
April 7:              Pluto at western stationary point at 8:38 hrs (diameter = 0.1")
April 9:              Mercury at Greatest Elongation East (19.11º) at 5:55 hrs (diameter = 7.6")
April 10:            Moon 3.9º north of Neptune at 7:19 hrs
April 12:            Moon 5.6º north of Jupiter at 2:48 hrs
April 12:            Moon 5.9º north of Uranus at 19:15 hrs
April 16:            Moon 1.6º north of Mercury at 7:58 hrs
April 16:            Moon 4.4º north of Venus at 21:05 hrs
April 17:            Moon  occults stars in the Pleiades cluster between 15:06 and 18:45 hrs
April 18:            Mars 1.1º north of the Praesepe star cluster at  3:50 hrs
April 18:            Mars 48 arcminutes south of the star Asellus Borealis (Gamma Cancri, mv = 4.66) at 18:52 hrs
April 18:            Mercury at eastern stationary point at 14:00 hrs (diameter = 9.9")
April 22:            Moon 3.7º south of Mars at 16:39 hrs
April 26:            Moon 10.2º south of Saturn at 15:57 hrs
April 29:            Mercury at inferior conjunction at 2:51 hrs
 

The Planets for this month: 

 

Mercury:   The innermost planet is difficult to observe this month, due to its proximity to the solar glare. It is presently heading around to the other side of the Sun, and will pass through superior conjunction on March 14. Mercury will then return to the evening twilight sky. .

 

Venus: The brightest planet passed behind the Sun (superior conjunction) on January 12. It has now returned to the western twilight sky, but will be close to the horizon at the beginning of the month. Look for it due west as soon as the sun has set and the sky begins to darken. It will be easier to find later in the month.

(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).

         March, 2010                       August, 2010                          October, 2010      

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. Up until the end of March, Venus appeared as an 'Evening Star', but this month it becomes a 'Morning Star' once again. Each of these appearances lasts about eight to nine months.

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

 

Mars:   Over the last few months, the red planet has been moving eastwards through the zodiacal constellations Taurus, Gemini and Cancer, gradually brightening and becoming larger in angular size as the Earth, travelling faster, catches it up. Mars passed from Cancer into Leo on November 30. On December 21 it ceased this eastwards motion, reversing direction and heading back towards Cancer, which it re-entered on January 12. 

This apparent reversal of motion is not due to any change in Mars's orbital movement, but is a perspective effect caused by the Earth beginning to overtake Mars, and our faster speed makes Mars appear to be going backwards, relative to us.

This reversal, called a 'retrograde loop', was very difficult for ancient astronomers to explain, for they believed that all the planets, including the Sun and Moon, circled an unmoving Earth. It was not until the time of Nicolaus Copernicus in the 16th century, that the retrograde movements of Mars and the other outer planets could be properly explained, by putting them all, including the Earth, in orbit around the central Sun.

Mars will complete its retrograde loop in Cancer on March 11, and will then head east again, returning to Leo on May 13. The period when Mars is in its retrograde loop is when it is at its largest and brightest. The mid-point of the loop is the time when the Earth actually passes Mars. This is called the 'opposition' of Mars, as it is in the exact opposite direction to the Sun - when the Sun sets, Mars rises. The opposition of Mars occurred on January 30.

March is still a good time for observing Mars, but it is not as large and bright as it appeared at closest approach at the end of January. It is a brilliant naked-eye object, orange in colour, and brighter than all of the stars except for the brightest six (Sirius, Canopus, Arcturus, Alpha Centauri, Vega and Rigel). On March 1, Mars will be a little more than two handspans above the northern horizon at 9:30 pm.

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.

 

Jupiter:  The giant planet is now impossible to observe, having passed through conjunction (behind the Sun) on February 28. It is presently in the constellation of Aquarius.

 

Saturn:  The ringed planet is in the constellation Virgo, and rises due east at about 7:30 pm in early March. Saturn’s rings are a magnificent sight, but at present they are very narrow, but slowly widening. In early October 2009 a new, large ring around Saturn was discovered by the Spitzer Infrared Space Telescope. Although the new ring cannot be seen by ordinary telescopes, the familiar ring system seen in visible-light images can be detected in even the smallest telescope.

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

 

Uranus:  This planet will reach conjunction on March 17, which means that it is extremely difficult to observe during March.

 

Neptune:  The icy blue planet is at present difficult to observe, having passed through conjunction on February 15. It will re-appear in the morning sky late in the month. 

Neptune, photographed from Nambour on October 31, 2008

 

Pluto:  The erstwhile ninth and most distant planet is a faint 14.1 magnitude object in the constellation Sagittarius, near the boundary with Serpens Cauda (The Snake's Tail). It is about 5 degrees north-east of the Trifid Nebula, M20. A powerful telescope is needed to detect Pluto, which even under excellent seeing conditions appears as a very faint star-like object. It is passed on the far side of the Sun on December 25, and now is a morning sky object, rising mid-month soon after midnight. Its angular diameter is 0.13 arcseconds, less than one twentieth of the size of Neptune.

  

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

 

 

Meteor Showers:  

Lyrids           April 23                      Waxing gibbous Moon, just past First Quarter, 58% sunlit                     ZHR = 15
                                      Radiant:  Near the star Vega. 

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'. One caused great alarm in Canada recently, being recorded on a camera mounted on the dashboard of a police cruiser. 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 heading towards the outer Solar System, and has faded below magnitude 12.

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

The LINEAR robotic 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. Needless to say, Comet Machholz was discovered in one of these gaps by an amateur astronomer with a small backyard observatory.

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 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.

 

The Eta Carinae Nebula, to the right of the Southern Cross tonight

 

 

The Stars and Constellations for this Month:

 

These descriptions of the night sky are for 9 pm on March 1 and 7 pm on March 31. They start at Orion, which is very high in the north-west.

This month, Orion (see below) is high in the north-west. By mid-month, Orion will have set by midnight. Canis Major (the Large Dog) is just west of the zenith at this time, with the brilliant white star Sirius (Alpha Canis Majoris) showing the Dog's heart. Sirius, the Dog Star, is the brightest star in the night sky and is about a handspan from the zenith. Directly overhead is the constellation, Puppis, the Stern (of the ship, Argo). Orion will have set by midnight.

The brilliant white star Rigel (Beta Orionis) is about two handspans west of the zenith at this time. 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 7.00 pm at mid-month. Directly overhead is a faint constellation, Columba, the Dove.will culminate at 9.00 pm in mid-month.

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. This month, Mars outshines Sirius. The faintest stars on this image are of magnitude 15.

The constellation Taurus with the clusters 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. It is only half as far away as the Hyades. 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. 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 will have disappeared by 10.00 pm early in the month, and the rest of Taurus follows them below the horizon soon after.

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 formed the Pleiades can be seen around the brighter stars in the cluster.

Between Orion’s head and the north-western horizon is a large constellation shaped roughly like a pentagon. It is east of Taurus. This is Auriga the Charioteer, its brightest star being Capella, at the bottom of the tilted pentagon. Capella is the fifth brightest star in the sky, after Sirius, Canopus, Alpha Centauri, Beta Centauri and Vega. To the left of Capella 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.

To the east of Auriga, Gemini is quite high, the two twin stars at its eastern end, Pollux and Castor being due north. At 9.00 pm at the beginning of month they are straddling 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 at culmination. At that point, it ceases rising and begins setting. The Twins will have set by 1.30 am.

Tonight, at a little over two handspans above the northern horizon, and directly above Pollux and Castor, is the first magnitude star Procyon, which is the brightest star in the constellation Canis Minor (the Small Dog).

High in the north-east is another zodiacal constellation, Leo, the Lion. The bright star Regulus (Alpha Leonis) marks the Lion’s heart, and Denebola, the star marking the tip of the lion's tail, is low in the east-north-east. From the southern hemisphere, we always see the Lion upside-down. His head and mane are marked by a curved line of stars shaped like an upside-down question mark. This line is also known as the 'Reaping Hook' or 'Sickle', the star Regulus marking the end of the Sickle's handle.

A little less than a handspan to the right of Denebola, we can see a brighter object. This is the planet Saturn, shining at magnitude -0.67. It is famous for its remarkable ring system, which can be easily seen in a small telescope and in fact can be glimpsed when wide open with a magnification of only 30 times. Saturn has over 63 satellites, but only seven are large enough to have pulled themselves into a spherical shape. Saturn's light currently takes a little over an hour to reach us. Saturn rises above the eastern horizon a little before 8 pm on March 1.

 

Between Gemini and Leo is the faint constellation of Cancer the Crab. Though a fairly unremarkable constellation in other ways, Cancer does contain a large star cluster called Praesepe or the Beehive, which is a good sight in binoculars. Also known as M44 *,, Praesepe is a little more than halfway along a line between Pollux and Regulus.

Mars is presently in Cancer, and this month is heading towards Praesepe. It will pass within one degree of the cluster on the night of April 17-18.

Rising above the eastern horizon is the next zodiacal constellation after Leo, Virgo, the Virgin. The brightest star in Virgo is Spica, an ellipsoidal variable star whose brightness averages magnitude 1. This makes it the sixteenth brightest star, and its colour is blue-white. Spica is about 10 degrees above the theoretical eastern horizon at this time.

Between the stars Regulus and Spica, we can see a bright object in the centre of Virgo. This is the planet Saturn, shining at magnitude 0.5. It is famous for its remarkable ring system, which can be easily seen in a small telescope and in fact can be glimpsed with a magnification of only 30 times. Saturn has over 60 satellites, and its light currently takes a little over an hour to reach us. Saturn is due north at 12.30 am at mid-month.

High in the east above Spica is the constellation Corvus the Crow, shaped like a quadrilateral of magnitude 3 stars. A large but faint constellation, Hydra, the Water Snake, winds its way from near Procyon around the north-eastern part of the sky at an altitude of about 60 degrees above the horizon. It passes over the top of Corvus and Virgo to end near Libra, which will not rise until 10.00 pm (at the beginning of the month).

Hydra has one bright star, Alphard, mv=2.2, which forms a roughly isosceles triangle with Jupiter and Procyon. 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 almost horizontal. The two Pointers Alpha and Beta Centauri lie below Crux. Crux will have rotated clockwise to a vertical position by 1.00 am at mid-month. Surrounding Crux on three sides is the large constellation Centaurus, and between Crux and the southern horizon are two brilliant stars, Alpha and Beta Centauri. Beta is the one nearer to Crux. These two stars are also known as 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.

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. Below and to the right of Alpha Centauri and underneath Musca is a (roughly) equilateral triangle of 4th magnitude stars. This is the constellation Triangulum Australe, the Southern Triangle. It is about half a handspan above the south-south-eastern horizon.

Between Crux and Sirius is a very large area of sky filled with interesting objects. This was once the constellation Argo, 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).

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

One and a half 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 a little more than a handspan above Crux and to the right, and is also lying on its side at this time of year. It is high in the south, and will soon culminate. 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.

A handspan above the south-south-western horizon is Achernar, Alpha Eridani. It is the brightest star in Eridanus the River, which winds its way with faint stars from Achernar in a northerly direction to Cursa, a mv= 2.9 star close to brilliant Rigel in Orion. At magnitude 0.49, Achernar is the ninth brightest star. It swings down towards the south-south-westerly horizon during the evening, and sets soon after midnight.

High in the south, about 43 degrees above the horizon, the Large Magellanic Cloud (LMC) is faintly visible as a diffuse glowing patch. It is a little less than a handspan below (south of) Canopus. About a handspan below the LMC is the Small Magellanic Cloud (SMC), a smaller glowing patch. The LMC and SMC are described below.

The zodiacal constellations visible tonight, starting at the western horizon and heading east (passing about two handspans north of the zenith, are Aries, Taurus, Gemini, Cancer, Leo and Virgo.

 

Mira, the Wonderful  

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

This drop of eight magnitudes means that its brightness diminishes over a period of five and a half months to one six-hundredth of what it had been, and then over the next five and a half months it regains its original brightness. To the ancients, they saw the familiar star fade away during the year until it disappeared, and then it slowly reappeared again. Its not surprising that it became known as 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.

Last November, Mira had brightened to second magnitude, but now it is fading once again. By May, it will have a visual magnitude (mv) of around 9, and will be in the faintest part of its cycle.     More about Mira      Mira's light curves and finder charts

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 on-going 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

 

The field of Mira, the Wonderful (circled)

    

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

 

 

The season of the Hunter and his Dogs:

Two of the most spectacular constellations in the sky may be seen near the zenith 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 Orion’s Sword. 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. Tonight this asterism appears right-side up, 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 nebulae). A photograph of it appears below:

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

The central section of the Great Nebula in Orion. At the brightest spot is a famous multiple star system, the Trapezium, illustrated below.

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

 

Canis Major:   

Above Orion as twilight ends (facing west), 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 heart of the hunter's dog, and has been known for centuries as the Dog Star. As we see him tonight, the dog is on his feet with his tail at upper left. A front leg stretches down from Sirius to 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 below Sirius.

The hindquarters of the Dog are indicated by a large right-angled triangle of stars located above and to the left of Sirius. The end of his tail is the top-left corner of the triangle, about one handspan south (above and to the left) of Sirius.

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

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

Canis Minor:   

By 8.00 pm at mid-month, this small constellation is about one and a half handspans due north of the zenith. 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 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) down 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 (a handspan above the south-south-eastern horizon) to Achernar (a handspan above the south-western horizon. At 8 pm at mid-month, both stars will be at similar altitudes and the line 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, like 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 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 Kent (Alpha Centauri) at left, and Beta Cygni (Albireo), at right.

     

     The binary star Rigel (Beta Orionis, left) 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. 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.