Sky Guide March 2023

Constellations represent groups of stars that have been given a name and more recently a border. Think of them as suburbs in the sky. For millennia they have been used as a tool to share lore and events. Today, the 88 western constellations, as recognised by the International Astronomical Union (IAU) are used to map the sky and assist in the search for astronomical objects. Every March, these constellations dominate our sky as seen from the southern hemisphere:

Taurus the bull, possibly the oldest of all western constellations, is low in the northwest. It is home to M1 the crab nebula formed by a star that exploded in 1054, M45 the Pleiades, a striking open cluster and the dying red star Aldebaran. 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.

Orion the hunter, is descending into March’s north-western sky sitting above Taurus the bull and followed by the faithful Canis Major. One of the most famous non-zodiac constellations, its three-star belt, lies close to the celestial equator. These stars also make the base of what many Australians refer to as the saucepan. Within the handle of the saucepan, or the sword for the traditionalists, a star making cloud, or nebula at around 1,350 light years away is one of the first things to look at through any telescope. M42 or the Orion nebula, contains enough gas and dust to make as many as 2,000 stars like the Sun. It is a stunning object to view on a dark moonless night.

Leo the lion, rising in the north-east, looks more like an upside-down question mark for us in the south than a lion’s mane as seen from the north. One of Ptolemy’s original 48 constellations from the 2nd century. Its brightest star Regulus (Little King) is a system of four tightly bound stars at 79 light years. Leo is host to several bright galaxies though these require large telescopes in dark locations to be seen. They are popular targets for amateur astro-photographers.

Canis Major high overhead lies the constellation of the big dog. Like many other constellations, a good imagination, and the ability to ‘see’ stick figures will help see the profile of a dog. It hosts the brightest star in the night sky, Sirius.

Crux or the Southern Cross, the smallest of the 88 commonly accepted constellations. It and the nearby pointers of Alpha and Beta Centauri are making their return to the evening sky low in the south-east. Light pollution and the thicker atmosphere near the horizon dims their starlight making them harder to identify in the early evening. They are at their highest and brightest at around 2am, due south. To find south, draw an imaginary line from the top of Crux though the bottom and across the sky to the brightest star in the constellation of Eridanus the river, Achernar. This is the least spherical star in the Milky Way with an equatorial bulge of about 50% more than its polar circumference. Halfway along that imaginary line, drop to the horizon to find south.

All 5 naked eye planets can be spotted at some point in the month.

Mercury is very low in the eastern morning sky in Capricornus before moving into Aquarius on the second. On 3 March, rising at 5:33am AEDT, it is in conjunction with Saturn before vanishing into the morning twilight by the end of the first week. A perfectly clear easterly view will be needed to spot the pair before civil twilight at 6:19am AEDT.

Venus is low in the west after sunset moving from Pisces to Aries. On 2 March, Venus will be in conjunction with Jupiter separated by distance of ½ a degree (the width of the Full Moon). On 24 March, Venus will be close to the crescent Moon. For the very keen, Venus will be close to Uranus on 30 and 31 March. While Venus will be very bright at magnitude (m) –3, Uranus will be too faint to be seen with the unaided eye at magnitude (m) 7. Binoculars or a small telescope will be needed and to find it, centre the view on Venus and then scan ever so slightly to the left and up looking for a small pale greenish blue dot, good luck.

Mars starts the month in the NNW in Taurus before moving into Gemini. On 28 March it will be above the waxing crescent (43%) Moon.

Jupiter is very low in the west in the early evening before fading from view by mid-month.

Saturn it will be low in the morning eastern sky in Aquarius. On 20 March it will be close to the waning crescent Moon.

Full Moon – Tuesday 7 at 11:40pm AEDT

Last quarter – Wednesday 15 at 1:08pm AEDT

New Moon – Wednesday 22 at 4:23am AEDT

First quarter – Wednesday 29 at 1:32pm AEDT

The Autumn equinox, when the Sun crosses from the southern to the northern sky, occurs on Tuesday 21 March at 8:24am AEDT. On this day, the Sun rises and sets due east and west. The length of day and night is almost equal but not quite.

Explore the universe through binoculars or a telescope and take in these gems of the March sky:

The Milky Way everything bar three objects we see with the unaided eye are part of our Milky Way galaxy, but to most people, the Milky Way is the bright core and side-on arms of our galaxy as seen from dark rural locations on a moonless night. It is perfect at this time of year around midnight. The faint glow of billions of stars extends from the low southeast across the sky to the northwest. No telescope is required and look for the head and neck of the emu in the sky.

The Great Nebula in Carina (NGC3372) rising high into the southeast, it is more than four times larger than the more famous Orion nebula. The distance of around 7,500 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. It contains some of the youngest star clusters in the Milky Way as well as one star 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.

The open clusters NGC 3293 and NGC 3532 both in Carina, 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 a distance of 1,300 light years. NGC 3293 is much younger with stars between 6 and 20 million years but around 9,000 light years away.

The Large and Small Magellanic Clouds are two of our Milky Way’s satellite galaxies. The Large Magellanic Cloud (LMC) in the constellation of Dorado is about 163,000 light years away, while the Small Magellanic Cloud (SMC) in Tucana is about 206,000 light years away. They are the brightest in the local group of about 30 nearby galaxies but are best seen away from cities and towns on moonless nights. They look like small parts of the Milky Way that have drifted away but are in fact approaching and are expected to merge with us in around 2.4 billion years.

Tarantula Nebula (NGC 2070) is a huge starburst nebula of hydrogen gas approximately 1,000 light years in diameter and 450,000 more massive than the Sun. It sits on the leading edge of the LMC, and several young massive stars have already exploded with the cloud.

M45 the Pleiades one of the more famous open clusters visible to the naked eye, lies within Taurus. 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. 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.

The Orion nebula (M42) the finest and brightest nebula in the sky, is now descending to the northwest. Sitting close to the celestial equator it is visible to the unaided eye in Orion’s sword from both hemispheres. It is approximately 1,344 light years away and 24 light years across. 700 young stars are in various stages of formation with 6 visible in the Trapezium in the heart of the nebula. In simple astrophotography with a DSLR on a tripod it starts to show the pink star-making colour of hydrogen gas but through telescopes and binoculars it is mostly grey green.