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Sky Guide February 2024

Sydney Observatory’s monthly guide to the southern sky
With Geoffrey Wyatt

With 29 days in February, 2024 is a Leap Year, or more precisely a Bissextile Year thanks to the naming conventions introduced under the reign of Julius Caesar in 46BCE. This extra day affords more time to enjoy the constellation of Orion in the north with the star forming cloud, M42 the Orion Nebula and the planet Jupiter in Aries to the northwest.
Geoffrey Wyatt

Constellations

Constellations are groups of stars that represent mythological figures, fanciful beasts or old scientific instruments. Some have been used for millennia as a tool to share significant cultural stories and to track the passage of the weeks and months. Today they also help astronomers mark out portions of the sky and locate astronomical objects. Those listed below have been selected for their visibility in the evening up to two hours after sunset in the southern hemisphere.

Canis Major the Greater Dog and companion to Orion the hunter is the brightest star in the constellation Sirius (also known as the Dog Star). It is also the brightest in the night sky as it is close to us – only 8.7 light years away or about 82 million million kilometres and 25 times brighter than the Sun. In about 64,000 years it will be seen as the southern polar star due to the Earth’s wobbling axis of rotation and the star’s proper motion.

Canis Minor the Lesser Dog is an obscure and small constellation usually ignored in the search for its dominant companion, Canis Major, the Greater Dog. To find its one bright star, face north in March – April and look for Sirius in Canis Major. Roughly one hand span (with your hand at arm’s length) below Sirius is the bright star Procyon. And Procyon is just about all there is to the Lesser Dog! Like many constellations it looks nothing like its name. The star’s name comes from the Greek Prokyon meaning ’before the dog’ and indeed it does rise before bright Sirius and Canis Major from the latitudes of ancient Greece. Canis Minor and Canis Major together are Orion’s hunting dogs.

Carina the keel and the nearby constellations of Vela (the sails) and Puppis (the stern) were part of the huge constellation Argo Navis, which in Greek mythology carried Jason and the Argonauts in search of the Golden Fleece of Aries the Ram. In 1756, Nicolas Louis de Lacaille published his catalogue of the southern stars showing Argo Navis divided into the four constellations we see today. Canopus, the second brightest star in the night sky, can be found in Carina and is a white supergiant star about 313 light years away. It is best seen from February to April high in the south.

Eridanus is one of Ptolemy’s original 48 constellations and represents a river, which begins near the constellation of Orion and ends at the brilliant, blue-white star Achernar, the ninth brightest in the night sky at about 144 light years away. Achernar spins so quickly it is the least spherical star known in the Milky Way galaxy with an equatorial diameter 35% greater than its polar diameter.

OBJECT NO. A7571-24
'Gemini' playing card from 'Urania's Mirror' card game

Gemini the twins with its two bright stars, Caster and Pollux, sits low in the northern sky between Taurus and Cancer and lacks any bright objects of note. It is best known for the Geminid meteor shower that peaks in the early hours of 13—15 December each year and for hosting both Uranus and Pluto when they were discovered in 1781 and 1930 respectively.

Orion the hunter is one of the original 48 constellations mapped by Ptolemy andstrides acrossthe celestial equator, making it easy to see from both hemispheres. Its likeness to a male figure was probably obvious to the earliest humans. Orion’s brightest star Betelgeuse is one of the few stars to show an intense red colour due to its age and size. The three stars of Orion’s belt at his waist separate his head andshoulders on the right from his sword and knees on the left. The well-known saucepan asterism (a pattern of stars that is not a constellation)consists of a base (Orion’s belt) and a handle (Orion’s sword) plus one additional star at the rim. With binoculars you will see a small hazy glow in the middle of the saucepan’s handle: this is the Orion Nebula, a star birth cloud at a distance of about 1350 light years. The mythology of Orion is complex and often contradictory, though he is usually representedas a tall, strong and handsome hunter.

Taurus the bull is possibly the oldest Western constellation and one of Ptolemy’s original 48. It has the bright red dying star of Aldebaran and the stunning open cluster known as M45 or the Pleiades, a group of very young stars about 445 light years away. Below the horns is the remnant of a star that exploded as a supernova in 1054. It is now called M1 or the Crab Nebula. For the best view you'll need a large telescope and clear northerly view.Its brightest star Aldebaran is 65 light years from the Sun and is 44 times wider but only a little more massive (+16%). It has exhausted its core supply of hydrogen fuel and is now ‘burning’ hydrogen in a shell around a helium core.

Titan and Saturn

Planets

Evening

Jupiter shines but the ringed planet Saturn is lost. Jupiter is in the north-west in Aries. On 15 February the crescent Moon is below and to the right or north of Jupiter.

Saturn is low in the west in Aquarius at the start of the month but disappears below the horizon after the first week

Morning

Mercury starts the month low in the south-east in Sagittarius, moving to Capricornus in the first weekend of the month. On 9 February a very thin crescent Moon may be visible above and to the right or south of the planet. Mercury fades into the twilight in the middle of the month.

Venus is in the east, moving from Sagittarius to Capricornus just after the middle of the month. On 8 February a very thin crescent Moon is above and to the right or south of Venus. From 22 to 24 February, Venus passes less than two Moon-widths from Mars.

Mars is in the east, moving from Sagittarius to Capricornus in the middle of the month.

OBJECT NO. 85/59-22/80
Glass plate slide of the California Nebula in the Perseus Constellation

Deep Sky

The Carina Nebula (NGC 3372) is more than four times larger than the more famous Orion Nebula (M42) seen in summer. Its distance of around 7500 light years disguises its immense size of around 500 light years in diameter. On a moonless night it is a stunning view through binoculars or a telescope as well as being visible to the naked eye. It contains some of the youngest star clusters in the Milky Way as well as a star already coming to an explosive death. The star Eta Carinae at 100-150 times the mass of the Sun is a dying cataclysmic variable which is expected to explode as a supernova anytime within the next million years. A supernova precursor eruption in the 1840s temporarily elevated it to the second brightest star in the night sky.

Crab Nebula (M1) is a remnant of a star that ended its life as a supernova visible from Earth on July 4, 1054AD. It was observed by Chinese astronomers. At the centre of this remnant is a pulsar which currently emits at a rate of 30 pulses per second though this rate will slow to half of this over the next 1000 years. The Crab Nebula lies about 6500 light years away.

The Large and Small Magellanic Clouds (LMC/SMC) are the two satellite galaxies of our own Milky Way. The Large Magellanic Cloud (LMC) is in the constellation of Dorado and is approximately 163,000 light years away. It consists of around 30 billion stars and hosts one of the largest nebulae detected, the Tarantula Nebula. The Small Magellanic Cloud (SMC) is in Tucana and is approximately 200,000 light years away. It has around 3 billion stars and will merge with our galaxy in around 2.4 billion years.

Orion Nebula (M42) is often called the Great Nebula in Orion and is approximately 1344 light years away. M42 is 24 light years across with enough mass to form around 2000 stars like the Sun. Its size, distance and brightness (it is the brightest nebula seen from Earth), make it one of the most studied objects in the night sky. It is easily found as the middle star-like object in the sword of Orion, or the handle of the saucepan as seen from the south. Along with the Moon, M42 is typically one of the first objects to be looked at through a telescope as it shows excellent fine structure including the birth of stars in the innermost part known as the Trapezium Cluster.

Pleaides (M45), alsoknown as Subaru, it is one of the more famous open clusters visible to the naked eye, sitting within Taurus the bull. Like all open clusters it is a group of young to middle aged stars, in this case around 100 million years old, at about 444 light years away. Many images show the stars associated with a dusty blue nebula however this lies between us and the stars. Curiously, these stars are often referred to as seven sisters.

NGC 3293 and NGC 3532 are two stunning open clusters in Carina, which are excellent targets for binocular and telescope viewing. NGC 3532 was the first target of the Hubble Space Telescope in 1990. It contains around 150 stars thought to be 300 million years old at 1300 light years. NGC 3293 is much younger with stars between 6 and 20 million years but around 9000 light years away.

The Tarantula Nebula (NGC 2070) is a large hydrogen gas cloud approximately 1000 light years in diameter and part of the LMC at about 160,000 light years. The name ‘Tarantula’ comes from the spider-like appearance of the nebula in telescopes and photographs. At the centre of the nebula is the open cluster R136, which contains approximately 500,000 stars, including some of the hottest and most massive supergiant stars known. In 1987 the first naked eye supernova (SN1987A) since the invention of the telescope occurred in this part of the sky.


Moon

Last quarter – Saturday 3 February at 10:18 am AEDT

New Moon – 10 Saturday 10 February at 9:59 am AEDT

First quarter –Saturday 17 February at 2:01 am AEDT

Full moon – Saturday 24 February at 11:30 pm AEDT