Northern HemisphereNorthern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during January 2015.

Orion is high in the south, pointing to other nearby constellations. Below Orion's famous Belt is his Sword, in the middle of which is the hazy glow of the Orion Nebula. This is an HII region in which stars are being born, and it is lit by the four stars of the Trapezium at its heart. Following Orion's Belt down to the left, you come to the brightest night-time star, Sirius. Following the Belt in the other direction brings you to the constellation of Taurus the Bull. The Hyades Cluster forms its head, while the red star Aldebaran represents its eye. A little further over is the Pleiades Cluster. Up to Orion's left is Gemini, the Twins, with the bright stars Castor and Pollux. Near the zenith is the yellow star Capella, in Auriga. The Milky Way runs through Auriga, giving it a number of open star clusters that can be seen with binoculars. Perseus and Cassiopeia lie north-west from here, along the Milky Way, with the Perseus Double Cluster between them. Leo the Lion rises in the east late in the evening, hosting the planet Jupiter at present.

The Planets

Jupiter, at magnitude -2.4, rises around 20:00 UT (Universal Time) at the beginning of January and is located 8.5 degrees up and right of the star Regulus in Leo. It is moving retrograde (westward) towards Cancer, which it will reach next month, and by the end of January it rises at 17:45 and shines at magnitude -2.6. It then reaches a maximum elevation of 56 degrees when due south around 01:00. Jupiter's apparent size grows from 43.4 to 45.3" during the month, and its equatorial bands and Great Red Spot are visible to a telescope, while observing its four largest moons requires only binoculars.

Saturn rises at about 05:00 UT at the start of the month and 03:30 by its end. It moves from Libra into Scorpius on the 4th, moving above the star Antares and the head of Scorpius. It grows from 15.5 to 16.1" during January, ending the month at magnitude +0.6 and high enough in the south-east before dawn to allow a telescope to make out its rings, which are now 24 degrees to our line of sight.

Mercury is low in the south-west before dawn on New Year's Day, 3 degrees down to the right of Venus and shining at magnitude -0.8. Mercury and Venus then stay within 1 degree of each other from the 8th to the 12th. Mercury's gibbous disc is 6.5" across, and it reaches greatest eastern elongation east (its furthest from the Sun in the sky, on this occasion 19 degrees away) on the 14th. Over the following week, it wanes in phase and drops to the lower right of Venus, disappearing from view as it moves between the Earth and Sun (inferior conjunction) on the 30th.

Mars starts the month in Capricornus and moves into Aquarius on the 8th. It dims slightly from magnitude +1.1 to +1.2 during January, while its disc shrinks from 4.8 to 4.4". It is best observed as darkness falls, low above the south-western horizon, but its small size and low elevation prevent surface details from being seen. Mars lies 24 degrees up and left of Venus as the year opens, and sets around 3 hours after the Sun all month as it progresses eastwards relative to the stars.

Venus shines at magnitude -3.9 and, as the month begins, sets in the south-west just over an hour after the Sun. Its angular size increases from 10.3 to 10.8" during January; Earth's atmosphere blurs its disc, but may also split its colours to produce a spectrum that can be seen with a telescope.

Highlights

• Mercury and Venus appear just 39' apart after sunset on the 10th, low in the south-west. Mars is found higher and further south at the same time.
• Saturn is 3.5 degrees to the lower left of a waning crescent Moon an hour before dawn on the 16th.
• A waxing gibbous Moon can be seen about 1 degree up and left of the star Aldebaran and the Hyades Cluster after sunset on the 29th, having passed in front of them earlier in the day.
• The night of the 29th is a good time to observe the lunar craters Tycho and Copernicus using binoculars or a telescope. Tycho, the younger crater at around 108 million years old, is towards the bottom of the Moon in the Southern Lunar Highlands and may have been made by the impact of a Baptistina Family asteroid. It is 85 kilometres across and nearly 5 kilometres deep, and the rays of material shed by the impact can be seen arcing across the Moon's surface. Copernicus, some 800 million years old, lies in the easterly Oceanus Procellarum, beyond the end of the Apennine Mountains. It is a terraced crater, 93 kilometres wide and almost 4 kilometres deep. The Moon can be imaged very well using relatively simple equipment and processing.

Southern Hemisphere

Claire Bretherton from the Cearter Observatory in New Zealand speaks about the southern hemisphere night sky during January 2015.

The Earth reaches its annual perihelion (its closest to the Sun) on the 4th, but the extra solar radiation has only a small effect compared to the seasonal tilt of the planet's axis. With the summer solstice passed, the nights gradually begin to grow longer, and the Milky Way stretches across the eastern sky after dark. The brightest area is towards the Galactic centre, near the constellation of Crux, which to Maori is Te Punga, or the Anchor. Also known as the Southern Cross, Crux is near to the asterisms of the Diamond Cross and the False Cross. Canopus, the second-brightest star in the night sky at magnitude -0.7, sits above the Milky Way and never sets over New Zealand. It is known to Maori either as Ariki, meaning high-born, or as Atutahi, meaning stand-alone, and is considered Tapu, or sacred. Canopus is the brightest star in the constellation of Carina, the Keel, which once formed part of the great constellation of Argo Navis. This area of the sky hosts many nebulae and star clusters, including NGC 3372, the Carina Nebula. A huge cloud of glowing gas, it is one of the largest nebulae in our sky, and its bright centre is visible to the naked eye. Binoculars can pick out Eta Carinae, the golden star at the heart of the nebula, which is actually a system of two known stars. With a total combined luminosity of some five million times that of our Sun, these stars are very large, the bigger of the two barely held together by gravity as its intense radiation pushes outwards and drives a stream of material into space. Eta Carinae has changed brightness greatly over the last 350 years, varying from magnitude +4 in 1677 to -0.8 in 1843. Now back at around 4, it seems to be brightening once again, and the variation is believed to result from sudden outbursts of material.

Eta Carinae is part of the huge open star cluster Trumpler 16, which contains many young stars. The nearby open cluster Trumpler 14 is currently forming massive stars. IC 2602, known as the Theta Carinae Cluster or the Southern Pleiades, is about 4 degrees south of Carina. Home to around 60 stars and covering an area greater than that of the full Moon, its magnitude of +1.9 makes it a good target for the wide field of a pair of binoculars. NGC 2516 and NGC 3532 are other naked-eye open clusters in Carina that look spectacular in binoculars.

The Planets

• Brilliant Venus follows the Sun in the sky, setting around an hour after it throughout January.
• Mercury follows the Sun even more closely, and appears near to Venus in the south-western twilight for the first half of the month. It reaches eastern elongation (its greatest separation east from the Sun in the sky) on the 15th, before rapidly disappearing in the Sun's glare until next month. Due to their proximity to the Sun, Mercury and Venus never stray far from it in our sky, always appearing shortly before dawn or after nightfall.
• Red Mars is above and to the right of Venus and Mercury, and approaches Venus during the month. At a present distance of around 300 million kilometres from Earth, its disc appears tiny in a telescope. It sets at about 23:30 NZDT (New Zealand Daylight Time, 13 hours ahead of Universal Time) at the beginning of January, but by the end can only just be seen only as daylight vanishes.
• Jupiter becomes more prominent in the evening sky this month, rising in the east-north-east at 23:00 NZDT at the start and at 21:00 at the end.
• Saturn is a pre-dawn object, but rises ever earlier in the east-south-east as January progresses.

Highlights

• Comet C-2014 Q2 (Lovejoy) is brightening in the southern sky. First spotted at magnitude +15 in Puppis by amateur astronomy Terry Lovejoy, it reached +6 in mid-December as it approached the Sun. Early in January, its position in the sky moves from Lepus to Eridanus and then to Triangulum, and it may just be visible to the naked eye in Taurus on the 10th, although the Moon will hamper viewing. Comet Lovejoy disappears from New Zealand's skies in mid-January as it progresses northwards.