The Evening Sky in January 2023
Bright planets and bright stars are scattered over the evening sky. Silver Venus is the brightest ‘star’ in the early evening sky, low in the southwest at dusk, setting 70 minutes after the Sun. Golden Jupiter, second brightest after Venus, is in the northwest. It sets due west around midnight. Orange Mars, low in the north, is the brightest ‘star’ in that part of the sky. Saturn looks like a medium-brightness star above Venus at the beginning of the month. It slips lower. On the 22nd Saturn will be just a full-moon’s width right of Venus. On the 23rd the thin crescent Moon will be near the two planets. The Moon will be near Mars on the 3rd and 4th and again on the 31st. It will be near Jupiter on the 21st.
Jupiter is worth a look in any telescope. Small telescopes show its disc and its four big moons. We are viewing their orbits edge-on so they appear to slide back and forth, night to night, like beads on a string. Larger telescopes show dark stripes in Jupiter’s clouds. Mars, though bright, is small in a telescope. It will slowly fade as we leave it behind.
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. 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.
Below and left of Orion and above Mars 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, making one eye of the bull, is not a member of the cluster but on the line of sight, at half the cluster's distance.
Left of Mars 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 Aotearoa 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 Milky Way is faint left, or north, of Orion because we are looking toward its thin outer edge. The centre region of the Galaxy, in Sagittarius, is hidden by the sun at this time of year.
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.
*A light year is the distance that light travels in one year: nearly 10 million million km or 10^13 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.