The Mars Apparition of 2009-2010

by Martin J. Powell

Following superior conjunction on December 5th 2008 (when it passed directly behind the Sun) Mars emerged in the dawn sky in February 2009 as a relatively dim 'morning star', rising shortly before the Sun. Through the first half of 2009, the planet was best seen from the Southern hemisphere, although the planet's great distance and small apparent size during this period made it a disappointing sight when observed through telescopes. For Northern hemisphere observers, viewing circumstances were poor throughout the first half of 2009, with Mars appearing low down in the Eastern sky at dawn. Seen from the Northern hemisphere, Mars did not become a prominently visible object until late July 2009, by which time the long summer twilight was starting to recede and the planet was rising about four hours before the Sun. Viewing circumstances improved for both hemispheres as 2009 progressed.

From early 2009 through to August 2009, Mars moved steadily Eastwards (direct motion) through the following constellations, slowly brightening as its distance from Earth reduced:

On August 25th 2009, Mars crossed the boundary from Taurus, the Bull, into Gemini, the Twins. Mars brightened significantly from late September 2009 and its coloration began to appear more distinct. On October 12th 2009, the planet entered Cancer, the Crab, the faintest constellation of the zodiac and therefore the least easy to identify. From late October 2009 through to mid-May 2010, city-dwellers, struggling to discern Cancer under light-polluted skies, found Mars occupying the large, dark 'gap' in the night sky between Gemini and Leo; to find these two constellations from The Big Dipper (or The Plough), refer to the animation below.

From late October to early November 2009, Mars crossed the star cluster Messier 44 (M44 or NGC 2632) commonly known as Praesepe (pronounced 'pree-SEE-pee') which is visible to the naked-eye as a hazy patch of light (for more details, see below). City-dwellers detected the cluster easily with binoculars when panning the area of the sky immediately around Mars.

On November 30th 2009, Mars entered Leo, the Lion, where it remained for the next six weeks. Mid-way through its vacation, on December 21st 2009, the planet reached its Eastern stationary point, five degrees South of the star Alterf ( Leonis, mag. +4.3). The Red Planet returned to Cancer on January 10th 2010, now moving retrograde (East to West).

Mars reached opposition (i.e. its brightest for this apparition) on the night of January 29th 2010. Note that, although opposition took place on this date, Mars' closest approach to the Earth (at 0.6639 Astronomical Units or 99.33 million kms) took place two days earlier - on January 27th 2010 - because of the planet's eccentric orbit.

At opposition, a planet is positioned directly opposite the Sun in the sky (rising around sunset and setting around sunrise) and is visible throughout the night. Its highest point in the sky is reached when it crosses the observer's meridian at local midnight (due South in the Northern hemisphere, due North in the Southern hemisphere). A list of maximum altitudes and directions of the planet at several opposition dates for various latitudes is given on the current Mars page.

With an apparent magnitude of -1.3 and a maximum apparent disk diameter of 14".1 (14.1 arcseconds, where 1 arcsecond = 1/3600th of a degree), Mars at this opposition was not as bright nor as large (when seen through a telescope) as it was at its previous opposition in December 2007, when the planet reached magnitude -1.6 and had an apparent diameter of 15".8. This is because, at the 2010 opposition, the planet was further away from the Earth than it was at the 2007 opposition.

At its next opposition in 2012, the Red Planet would be even further from the Earth, appearing smaller still (13".9) and fainter (mag. -1.2). At this time, Mars would be near the point in its orbit when it was most distant from the Sun (a point called aphelion); such oppositions are often referred to as aphelic oppositions (for more details, see the Mars Oppositions page).

Mars faded rapidly after opposition as its distance from Earth increased, but it remained visible for a further 10 months in the evening sky, slowly closing in on the setting Sun. Mars reached its Western stationary point in Western Cancer, 7°.2 North-west of Asellus Borealis and 7°.7 South-west of Pollux, on March 11th 2010. The planet left Cancer and entered Leo once more on May 12th 2010, where it stayed for a little over two months before entering Virgo on July 19th of that year.

By December 2010, Mars became lost from view in the dusk twilight. The planet's furthest distance from Earth for this apparition (2.3793 AU or 356 million kms) was reached on January 7th 2011, when its apparent diameter was a mere 3".9 across.

Mars passed behind the Sun - at superior conjunction - on February 4th 2011. The 2011-2013 apparition began soon afterwards, which saw Mars in the constellation of Leo at its next opposition on March 3rd 2012 (for details, see the Mars 2011-13 page).

 [Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]

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Finding Mars in the Night Sky, August 2009 to July 2010

From late August to mid-October 2009, when Mars was moving through Gemini, The Big Dipper (The Plough) could be used to locate Gemini using the method shown in the animation here.

From late October 2009 through to about mid-May 2010, when Mars was moving through Cancer, the planet was found inside a triangle formed by the stars Regulus (in Leo), Castor (in Gemini) and Procyon (in Canis Minor). Throughout this period, Mars was brighter than any of the stars contained within this triangle, so observers in both town and city spotted Mars long before Cancer itself was identified.

Finally, from late May to mid-July 2010, when Mars was moving through Leo, The Big Dipper could be used to find Leo using the method shown in the animation referred to above.

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Bright Stars, Nearby Stars and Open Star Clusters

From November 2009 to early April 2010, Mars was brighter than all of the stars shown on the star map. The four brightest stars shown are Procyon ( Canis Minoris, magnitude +0.4), Pollux ( Geminorum, mag. +1.1), Regulus ( Leonis, mag. +1.3) and Castor ( Geminorum, mag. +1.6). Mars was brighter than both Regulus and Castor throughout the period, and was only exceeded in brightness by Procyon prior to November 2009 and after mid-April 2010. The planet was brighter than Pollux as it entered the star chart (late August 2009) and only became fainter than it after mid-June 2010.

Procyon, in the constellation Canis Minor (the Lesser Dog) is the eighth brightest star in the night sky and the fourth brightest Northern celestial hemisphere star. Procyon is a Greek name meaning 'before the dog', referring to the fact that it rises before the 'Dog Star', i.e. Sirius ( Canis Majoris, mag. -1.4, the brightest star in the night sky). Canis Minor contains little of interest for the binocular or telescopic observer, except for a few double stars. Procyon itself is interesting in that it has a companion white dwarf star (Procyon B), of very high density, orbiting the primary star (Procyon A) every 41 years. Procyon B is 11th magnitude and lies too close to Procyon A to be detectable in anything but professional telescopes; indeed, it was not discovered until 1896. Procyon is 11.4 light years distant (where 1 light year = 63,240 AU), meaning that it takes light 11.8 years to traverse the distance, and is one of the nearest stars to the Earth. Sirius is however closer still, at 8.6 light years and co-incidentally it also has a white dwarf companion.

Gemini's leading stars Castor and Pollux are named after the twins of Queen Leda of Sparta in ancient Greek mythology; the Romans identified them with the brothers Romulus and Remus who, according to ancient tradition, founded the city of Rome. The two stars are seperated by 4°.5, providing a useful reference for measuring angular distances in the night sky. The constellation's Western half is set against the backdrop of the Milky Way, so this region contains several open star clusters (groups of young stars within our galaxy which have been formed from the same nebulous cloud) and nebulae (interstellar clouds of gas and dust). The whole constellation also features numerous double stars and multiple stars.

Castor is part of a complex star system. The main star (Castor A) has a companion (Castor B, mag. +2.9) about 4".6 (4.6 arcseconds) away from it; a small telescope will be able to split the two. Larger telescopes will reveal a third star (Castor C or YY Geminorum) of ninth magnitude, some 70" away. Not visible in amateur telescopes is an additional companion star to each of these three stars, making Castor a sextuple star system. Castor and Pollux lie at distances of 52 light years and 34 light years from Earth, respectively.

During the final days of August and into early September 2009, Mars passed close to three bright stars and one open star cluster, all situated towards the 'foot' of the Western Twin.

Gemini's Westernmost bright star is 1 Geminorum (mag. +4.1); Mars passed 0°.3 North of this star on August 27th 2009. Sir William Herschel discovered Uranus in the vicinity of this star in March 1781; the blue-green planet was then situated just across the border in Taurus.

A short distance North-east of 1 Geminorum is the open star cluster M35 or NGC 2168. It can be glimpsed with the naked-eye on a dark, clear night as a small, misty patch of light. Mars passed 0°.8 South of the cluster on August 29th 2009. The cluster has an apparent diameter about the size of the Full Moon and it contains over 400 stars (!) It lies at a distance of about 2,800 light years from the Earth. Binoculars show a bright, elliptical glow with several stars, the cluster appearing somewhat 'doughnut-shaped' since there are considerably fewer stars at its centre. Small telescopes fitted with wide-field (low magnification) eyepieces show curving chains of stars from 8th to 12th magnitude. M35 is one of the more spectacular open star clusters in the night sky and astronomy authors have variously described its appearance as 'rich', 'beautiful', 'outstanding' and 'marvelous'!

The star Eta Geminorum ( Gem, mag. +3.1v), also known as Propus or Tejat Prior (meaning 'forward foot') is both a double star and a variable star. It has a close companion star of 8th magnitude which orbits the primary star once every 500 years; medium or large telescopes are required to resolve the pair. Tejat Prior is a red giant which fluctuates in brightness between mags. +3.1 and +3.9 over the course of about 230 days. Mars passed 1°.1 North of Tejat Prior on August 31st 2009. Three days later (September 3rd) the planet passed 1°.0 North of Mu Geminorum ( Gem, mag. +3.2v), or Tejat Posterior ('latter foot'). This is also a double star, having a ninth-magnitude companion positioned some 2' (2 arcminutes, where 1 arcminute = 1/60th of a degree) to the South-east of the primary, visible in small telescopes. The secondary star itself has a tenth-magnitude companion which requires larger telescopes to resolve.

On September 25th 2009, the Red Planet passed 0°.8 North of another double star, Wasat ( Geminorum, mag. +3.5), a name which is Arabic for 'middle'. The primary star is creamy-white and its magnitude +8.2 companion is orange. This pair should be easy to split, however the great brightness difference between the two stars makes them difficult to split in smaller telescopes. Astronomer Clyde Tombaugh discovered Pluto near Wasat in February 1930, while he was examining photographic plates of the region which had been taken between January 23rd and 29th of that year.

Cancer, the Crab, is the faintest constellation of the zodiac and therefore the most difficult to see, particularly from urban and suburban locations, where the limiting magnitude (the faintest stars visible at the observer's zenith) may only be around +4.0. Cancer's five brightest stars form a shape reminiscent of the Greek letter lambda in lower case (). The brightest star (mag. +3.5) has been incorrectly assigned the name Beta Cancri ( Cnc) where it should technically have been classed as Alpha (). The actual star carrying the designation Cancri is named Acubens (meaning 'claws', mag. +4.3). It is a double star with an 11th magnitude companion; a small telescope will resolve them.

The star Iota Cancri ( Cnc, mag. +4.0), at the Northern end of the Crab, is a double star with a magnitude +6.5 companion. The stars are seperated by a sizeable 30" (30 arcseconds) allowing the pair to be resolvable in 10x50 binoculars. Telescopes show the stars to be a pretty combination of gold and pale-blue.

Cancer contains two interesting open star clusters. M44 (NGC 2632) is known as Praesepe or 'The Beehive Cluster' because of its binocular resemblance to a cloud of swarming bees. It is visible to the naked eye as a hazy patch of light at the constellation's centre but is much better seen through binoculars and telescopes. It lies at a distance of about 520 light years and is thought to be about 650 million years old. Binoculars show around 50 stars contained in a field of view roughly 80' (80 arcminutes) across. Small to medium-sized telescopes reveal about 75 stars visible down to about magnitude 12, whilst large telescopes show around 300 stars down to 17th magnitude. Because of Praesepe's large area (it is 95' across) telescopes need to be fitted with wide-field eyepieces in order to appreciate the full splendor of this cluster.

Praesepe is positioned a short distance North of the ecliptic (the apparent path of the Sun, which the Moon and planets follow very closely), so planets regularly pass across it in rather spectacular fashion. In 2009, Mars crossed the cluster between October 31st and November 2nd - a pretty sight when seen through binoculars.

The following day (November 3rd 2009), Mars passed mid-way between the stars Asellus Borealis ( Cancri, mag. +4.7) and Asellus Australis ( Cancri, mag. +3.9). Bizarrely, the names mean 'northern donkey' and 'southern donkey' respectively. This probably relates to the fact that M44 is sometimes referred to as 'The Manger' in reference to the Nativity story; in this case the donkeys are considered to be feeding at the Manger. Mars again passed between these two stars on April 19th 2010, although on this occasion it was positioned closer to Asellus Borealis, being 0°.8 to the South of it.

M67 (NGC 2682) is located 1°.7 to the West of Acubens. It is smaller and denser than M44 and is just beyond naked-eye visibility. There are over 300 stars in the cluster, which lies about 2,600 light years away. Binoculars show it as a small, hazy patch; small telescopes reveal about 20 stars down to 11th magnitude and medium-sized telescopes show around 50 stars down to 12th magnitude. With an estimated age of 5 billion years, this is one of the oldest known open star clusters, containing several red giant stars nearing the end of their lives.

Leo is perhaps the most recognisable of the zodiac constellations, and one of the few which bears a resemblance to the animal it is supposed to represent - a crouching Lion. The Lion's head and 'mane' are an asterism of its six Westernmost stars commonly called the Sickle of Leo, which is shaped like a backward question-mark [] At the base of the question-mark is Leo's brightest star, Regulus. It is also the closest bright star to the ecliptic, lying about 0°.5 degrees away from it. One consequence of this is that the star is regularly passed by the Moon and planets - indeed, Mars passed 0°.9 North of it on June 6th 2010. The fact that the name Regulus and the word 'Regal' are similar is no coincidence; Regulus is Latin for 'Little King', reflecting an ancient belief that it controlled the affairs of the heavens. It was given the name in the sixteenth century by the famous Polish astronomer Nicolaus Copernicus.

Approximately mid-way between the 'upper hind leg' stars Coxa ( Leonis, mag. +3.9) and Leonis are a pair of galaxies about 37 million light years away. M65 (NGC 3623, mag. +9.5) and M66 (NGC 3627, mag. +8.8) are positioned 20' (0°.3) apart and are among the brightest of many dozens of galaxies which exist in the constellation of Leo. M65 and M66 appear relatively bright and elliptical through small telescopes, orientated in a North-South direction. They are just discernible through binoculars in dark, moonless skies as faint, circular hazy patches of light.

Finally, on July 12th 2010, Mars passed 1°.0 South of the star Sigma Leonis ( Leo, mag. +4.0) at the 'foot' of Leo's hind leg. One week later, the planet moved from Leo into Virgo and out of the star chart coverage (the path of Mars from this date is continued on the Venus 2010 page).

Other constellations on the chart contain objects of interest which observers may wish to track down, and these will now be discussed briefly.

The constellation Monoceros, the Unicorn, is positioned between Procyon and Sirius. The fact that it is outshone by these two luminaries somewhat detracts from the fact that it contains a number of interesting star clusters and nebulae. Perhaps the most interesting of these is the Rosette Nebula (NGC 2237), an emission nebula which glows by emitting light from the radiation of the young, hot stars contained within it. The Rosette is about 4,700 light years distant and appears much like a beautiful pink carnation in long-exposure photographs. Alas, it is too faint to be seen in binoculars and small telescopes; medium and large telescopes are only likely to reveal the nebula's brightest regions when seen under very dark skies. More obvious to binocular and small telescope observers will be the star cluster at the nebula's centre (NGC 2244) comprising numerous stars of sixth magnitude and fainter.

In the Southern part of Monoceros is the open star cluster M50 (NGC 2323), about 2,600 light years distant. Its brightest stars can be seen in binoculars but a telescope is needed to resolve its 150 or so stars.

The Christmas Tree (NGC 2264) is an open star cluster with an associated nebulosity known as the Cone Nebula. The nebula is too faint to be seen in amateur telescopes, but the cluster's leading star, fifth-magnitude S Monocerotis (or 15 Mon), situated at the Northern end (base) of the 'Tree', is easily seen in binoculars, along with about 20 other stars down to about ninth magnitude. The 'Christmas Tree' appears inverted to Northern hemisphere observers and upright to Southern hemisphere observers. Appropriately, the Christmas Tree cluster crosses the observer's meridian (due South in the Northern hemisphere, due North in the Southern hemisphere) at local midnight around Christmas time.

Leo Minor (the Little Lion or Lion Cub), situated between Leo itself and Ursa Major, is fainter even than Cancer. It contains no stars brighter than magnitude +3.8 and there are no deep-sky objects (star clusters, nebulae and galaxies) to view in moderate-sized telescopes or binoculars. Because of a 19th century error when assigning star labels, this constellation has no star named Alpha () Leonis Minoris, although this should technically have been assigned to its brightest star, 46 Leonis Minoris.

Lynx, like Leo Minor, is a relatively recent constellation, having been introduced in the 17th-century by the Polish astronomer Johannes Hevelius. It bears no resemblance to a lynx and was in fact so-named because, as Hevelius put it, "only the lynx-eyed would be able to see it"! Lynx contains numerous double stars and multiple stars of interest to the amateur observer.

Hydra, the Water Snake, is the largest constellation in the sky, extending across 95° of celestial longitude; only its Northern section is included in the star chart. Hydra snakes its way between no less than ten constellations, starting just South of Cancer and ending just to the South of Libra. Hydra's brightest stars are all found in its Northern half, at the top of which is an asterism of six stars which form the distinctive shape of the Water Snake's head.

Close to Hydra's Western border with Monoceros is the open star cluster M48 (NGC 2548). It is about 2,000 light years away and comprises some 80 stars, covering an area about the same apparent size as the Full Moon. Under dark skies, the cluster can just be seen with the naked-eye as a hazy spot and around 50 stars of the group can be resolved in binoculars. Telescopes reveal several yellowish stars along with mostly white ones, some of them double.

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Moon near Mars Dates, September 2009 to December 2010

The Moon is easy to find, and on one or two days in each month, it passes Mars in the sky. The following tables list the dates on which the Moon passed near the planet between September 2009 and December 2010:

The Moon moves relatively quickly against the background stars in an Eastward direction, at about its own angular width (0º.5) each hour (about 12º.2 per day). Because it is relatively close to the Earth, an effect called parallax causes it to appear in a slightly different position (against the background stars) when seen from any two locations on the globe at any given instant; the further apart the locations, the greater the Moon's apparent displacement against the background stars. Therefore, for any given date and time listed in the table, the Moon will have appeared closer to Mars when seen from some locations than others. For this reason, the dates shown in the table should be used only for general guidance.

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Credits

• The star chart was created using a variety of sources, including the commercial software MegaStar (by Willmann-Bell, Inc), the freely-downloadable SFA Star Charts by Dan Bruton and the SkyGazer Ephemeris utility by John Biondo. Star colours were based on those shown in "Patrick Moore's Colour Star Atlas" (Mitchell Beazley Publishers Ltd., London, 1973).
• The times and separations of the lunar conjunctions with Mars (Moon near Mars dates) and the lunar phases were obtained from the commercial software RedShift 5 by Maris Technologies Ltd. using the 'Conjunctions' option of the 'Sky Diary'.
• The dates of Mars' closest approach to Earth and its greatest distance from Earth were derived from the SkyGazer Ephemeris utility and the NASA-JPL Solar System Simulator v4. The constellation boundary crossing dates were obtained from MegaStar.

• The zodiac signs are courtesy of the free graphics site .

Copyright  Martin J Powell  June 2009