The Evening Sky in January 2017
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The Evening Sky in January 2017
Brilliant Venus is the 'evening star', appearing due west after sunset. It sets around 11:30 at the beginning of the month, 10:30 by the end. Nearby, but much fainter, is reddish Mars. It is right of Venus and a bit higher in the sky at the beginning of the month. The gap closes so Mars is just above Venus by the 31st. In a telescope Venus looks like a tiny first-quarter Moon. It is 100 million km away at mid-month, catching up on Earth. Mars is 260 million km away, on the far side of the Sun; a tiny disk in a telescope. The Moon is near Venus on the 2nd and 31st, and Mars on the 3rd.
Mars passes the faint blue planet Neptune on New Year's Day but one needs a telescope to see it. Neptune is about 1/10th of a full-moon width (4') below and left of Mars. Neptune is 4.6 billion km from us. Mars moves on quickly. The Mars-Neptune gap is 1½ moon-widths (48') on the 2nd.
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 Pleiades/Matariki/Seven 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.
Jupiter, not shown, rises in the east around 12:30 a.m. mid-month. It is the brightest 'star' in the morning sky and shines with a steady golden light. Saturn is low in the eastern dawn sky below orange Antares. Mercury appears lower and right of Saturn but brighter.
*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.