The Evening Sky in January 2015
Whole sky chart for Jan 2015
The Evening Sky in January 2015
Brilliant Venus and bright Mercury make an eye-catching pair of "stars" low in the southwest at twilight. The two planets stay close together till mid month. After that Mercury sinks lower in the twilight as it moves between the Earth and the Sun. Venus remains low in the dusk as it slowly catches up with Earth from the far side of the sun. Above and right of Venus is a lone red "star", the planet Mars. Through the month Mars slips down the sky toward Venus. The two planets will be close together in late February. The apparent closeness of the planets is a line-of-sight effect. In mid-January Mercury is 144 million km from us; Venus 235 million km and Mars 304 million km.
An hour after Venus sets, at the beginning of the month, golden Jupiter rises on the opposite side of the sky. It rises earlier each night. By the end of January it will be in the northeast at dusk, the brightest "star" in the late night sky. Jupiter is 660 million km away
Sirius, the brightest true star, appears high in the east at dusk. Called 'the Dog Star' it marks the head of Canis Major the big dog. A group of stars to the right of it make the dog's hindquarters and tail, upside down just now. Sirius is the brightest star in the sky both because it is relatively close, nine light years away, and 23 times brighter than the sun. Procyon, in the northeast below Sirius, marks the smaller of the two dogs that follow Orion the hunter across the sky.
Left of Sirius as the sky darkens are Rigel and Betelgeuse, the brightest stars in Orion the hunter. Between them, but fainter, is a line of three stars making Orion's belt. Rigel is a bluish supergiant star, 70 000 times brighter than the sun and much hotter. It is 800 light years away. Orange Betelgeuse, below Orion's belt, is a red-giant star, cooler than the sun but hundreds of times bigger a ball of extremely thin hot gas. To southern hemisphere star watchers, Orion's belt makes the bottom of 'The Pot' or 'The Saucepan'. A faint line of stars above and right of the belt is the pot's handle or Orion's sword. It has a glowing cloud at its centre the Orion Nebula.
Left of Orion is the V-shaped pattern of stars making the face of Taurus the Bull. The V-shaped group is called the Hyades cluster. It is 150 light years away. Orange Aldebaran, Arabic for 'the eye of the bull', is not a member of the cluster but on the line of sight, half the cluster's distance.
Left again, toward the north and lower, is the PleiadesMatarikiSeven Sisters Subaru star cluster. Pretty to the eye and impressive in binoculars, it is 440 light years from us. From northern NZ the bright star Capella is on the north skyline. It is 90,000 times brighter than the sun and 3300 light years away.
Low in the south are Crux, the Southern Cross, and Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away. Canopus is also very luminous and distant 13 000 times brighter than the sun and 300 light years away.
The Milky Way is in the eastern sky, brightest in the southeast toward Crux. It can be traced towards the north but becomes faint below Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. Binoculars show many star clusters and a few glowing gas clouds in the Milky Way, particularly in the Carina region.
The Clouds of Magellan, LMC and SMC are high in the southern sky and easily seen by eye on a dark moonless night. They are two small galaxies about 160 000 and 200 000 light years away.
Saturn, not shown, rises in the southeast around 3 a.m. mid month. It is a creamy-white colour. To its right, and slightly fainter, is orange Antares. Saturn is 1570 million km from us.
A light year is the distance that light travels in one year nearly 10 million million km or 1013 km. Sunlight takes eight minutes to get here; moonlight about one second. Sunlight reaches Neptune, the outermost major planet, in four hours. It takes sunlight four years to reach the nearest star, Alpha Centauri.
Notes by Alan Gilmore,
University of Canterbury's Mt John Observatory,
P.O. Box 56,
Lake Tekapo 7945,