The Evening Sky in January 2025
Three bright planets make ‘evening stars’ in January. Venus is first to appear, low in the west. It is followed by Jupiter in the north, then Mars in the northeast. As the sky darkens Saturn appears near Venus, looking like a medium-brightness star. Venus sets around 11:40 at the beginning of the month and 11 at the end. Golden Jupiter is in the sky till morning hours and orange Mars is in the sky all night. Mars is at its closest for the year, 96 million km away, but small in a telescope. The Moon will be near Venus on the 3rd, between Venus and Saturn on the 4th, and near Mars on the 14th.
Sirius, the brightest true star, appears east of the zenith as the sky darkens. Canopus, the second-brightest star, is southeast of overhead. Achernar, fainter than Canopus, but one of the brightest southern stars, is southwest of overhead.
Sirius is called 'the Dog Star' because it marks the head of Canis Major the big dog. A group of stars to the right of Sirius make the dog's hindquarters and tail, upside down just now. Sirius is bright both because it is relatively close, nine light-years* away, and 23 times brighter than the sun. Procyon, in the northeast below Sirius, marks Canis Minor, 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. Rigel is a bluish supergiant star, 70 000 times brighter than the sun and much hotter. It is 800 light-years away. Orange Betelgeuse is a red-giant star, cooler than the sun but hundreds of times bigger: a ball of extremely thin hot gas. It is around 400 light-years away. 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.
Left of Orion, and just above Jupiter, 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 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 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. The Milky Way is faint right 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.
Mercury is in the dawn sky. It rises ESE around 4:50 on January 1st and 5:30 by the 21st.
*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.
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