The Evening Sky in January 2012

Venus and Jupiter are the 'evening stars' appearing soon after sunset. Brilliant silver Venus is low in the west. It sets in the southwest two hours after the sun. In a telescope it looks like a gibbous moon. Venus is on the far side of the sun from us, 180 million km away, slowly catching us up.

Jupiter is in the northwest at dusk. It sets around 1 am. It sets around 1 a.m. Its four big moons are easily seen in a telescope looking like stars lined up on either side of the planet. It is 720 million km away as we move to the far side of the sun from it.

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 makes 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.

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 400 light years from us. The cluster is around 70 million years old. From northern New Zealand the bright star Capella is on the north skyline.

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. A telescope shows it is a binary star: two stars orbiting each other in 80 years. 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.

Mars, not shown, rises due east around 12:30 a.m. at the beginning of the month. It looks like a bright orange-red star. By the end of the month it will be up around 10:30. It is brightening as we catch up on it. At mid month it will be 140 million km away so appears small in a telescope.

Saturn (not shown) rises due east about 2 am at he beginning of the month. By the end of January it will be up at midnight. It makes a pair with Spica, the brightest star in Virgo, above and left of Saturn. It is 1460 million km from us mid month.

Interesting Objects in the Southern Sky

Large and Small Clouds of Magellan (LMC and SMC) appear as two luminous clouds, easily seen by eye in a dark sky. They are galaxies like the Milky Way but much smaller. Each is made of billions of stars. The Large Cloud contains many clusters of young bright stars seen as patches of light in binoculars. Both clouds are about 160 000 light years away, very close by for galaxies. (1 light year is about 10 000 billion km.)

47 Tucanae, looks like a faint fuzzy star on the edge of the SMC. It is a globular cluster, a ball of millions of stars. A telescope is needed to see a peppering of stars around the edge of the cluster. Though it appears on the edge of the SMC it is one-tenth the distance, 15 000 light years away, and is has no connection to the Small Cloud. Globular clusters are mostly very old 10 billion years or more; at least twice the age of the sun. Omega Centauri, very low in the south, is a similar cluster.

 

The Tarantula nebula is a glowing gas cloud in the LMC. The gas glows in the ultra-violet light from a cluster of very hot stars at centre of the nebula. The cloud is about 800 light years across. It is easily seen in binoculars and can be seen by eye on moonless nights.

This nebula is one of the brightest known. If it was as close as the Orion nebula then it would be as bright as the full moon.

Canopus is the second brightest star. It is 14 000 times brighter than the sun and 300 light years away. Sirius, low in the east on spring evenings, is the brightest star in the sky.

Alpha Centauri the brighter pointer, is the closest naked-eye star, 4.3 light-years away. Alpha Centauri is a binary star: two stars about the same size as the sun orbiting around each other in 80 years. A telescope that magnifies 50x shows the pair. (A very faint star, Proxima Centauri, orbits a quarter of a light-year, or 15 000 Sun-earth distances, from the Alpha pair.)

Coalsack nebula, is a cloud of dust and gas about 300 light years away, dimming the more distant stars in the Milky Way. Many similar 'dark nebulae' can be seen, appearing as slots and holes in the Milky Way. These clouds of dust and gas eventually coalesce into clusters of stars.

The Jewel Box is a compact cluster of young bright stars about 7000 light years away. The cluster formed less than 10 million ago. To the eye it looks like a faint star.

Eta Carina nebula is a glowing gas cloud about 8000 light years away. The golden star in the cloud, visible in binoculars, is Eta Carinae. (Eta is the Greek 'e'.) It is estimated to be to be 60 times heavier than the sun and a million times brighter but is dimmed by dust clouds around it. It is expected to explode as a supernova any time in the next few thousand years.
Many star clusters are found in this part of the sky.

The Theta Carina Cluster, at one point of the 'Diamond Cross'. It is also known as the 'Five of Diamonds' cluster, the reason obvious when it is seen in a telescope. A newish name is 'Southern Pleiades', though this cluster is much fainter and smaller than the real Pleiades in Taurus. The cluster is about 500 light years away and is around 10 million years old.

NGC 2516, above the Diamond Cross, looks like a faint comet without a tail. It is a star cluster nicely seen in binoculars. It is 1200 light years away.

Interesting Objects in the Summer North Sky

Taurus the Bull and Orion the Hunter are prominent in our northern evening sky. Fainter and lower are Gemini the Twins and Cancer the Crab. The constellation pictures are upside-down to us; they were devised by northern hemisphere skywatchers. The face of Taurus is outlined by the V-shaped Hyades cluster. The brightest star in this group is orange Aldebaran, the name meaning 'the eye of the bull' in Arabic. Taurus's long horns extend down our sky. The Pleiades cluster rides on the Bull's back.

The Hyades cluster is 152 light years away. Its brightest stars (not Aldebaran!) are about 70 times brighter than the sun. The cluster is about 700 million years old. Aldebaran is not a member of the cluster but simply on the line of sight. It is 65 l.y. away and 150 times brighter than the sun. Aldebaran is a giant star about 25 times bigger than the sun though only five times heavier. Its orange colour is due to its temperature, around 3500° C. The sun is 5500° C.

The Pleiades / Seven Sisters / Matariki / Subaru, (left) and many other names, is a cluster of stars well known in both hemispheres. Though often called the Seven Sisters, most modern eyes see only six stars. Dozens are visible in binoculars. The cluster is about 400 light years away. Its brightest stars are around 200 times brighter than the sun. It formed about 70 million years ago.

Orion, in the northern hemisphere view, has a shield raised toward Taurus and a club ready for action. The line of three stars makes Orion's Belt. The line of faint stars above and left of the belt form Orion's Sword in the northern view, hanging from his belt. To most southern hemisphere sky watchers the belt and sword form The Pot or The Saucepan.

The Orion Nebula is visible in binoculars as a misty glow around the middle stars of Orion's Sword or the handle of The Pot. It is a vast cloud of dust and gas about 1300 l.y. away and more than 20 l.y. across. Ultra-violet light from a massive, extremely hot star in the cloud causes it to glow. Some stars in this region are around two million years old. The sun, by contrast, is 4.6 billion years old. Stars continue to form in a giant cloud behind the glowing nebula. There are many bright and dark nebulae in this region. The Horsehead nebula, a favourite of astronomy books, is beside the right-hand star of Orion's Belt, but too faint to be seen in small telescopes.

Rigel is a blue 'supergiant' star around 40,000 times brighter than the sun and 800 l.y. away. Its surface temperature is around 20,000°C, giving it a bluish colour. Betelgeuse is a red giant star 250 times bigger than the sun -- wider than earth's orbit! -- but only around 20 times heavier. It is mostly very thin gas surrounding a hot dense core. It is around 10,000 times brighter than the sun, about 400 light years away, and has a surface temperature around 3000°.

Sirius is the brightest star, though Venus and Jupiter, and sometimes Mars, are brighter. Sirius appears bright because it is both brighter than the sun -- 22 times brighter -- and relatively a close 8.6 l.y. away. Sirius was often called 'the dog star' being the brightest star in Canis Major, one of the two dogs that follow Orion across the sky.

The Praesepe cluster or Beehive cluster, low in the northeast in the later evening, marks the shell of Cancer the crab. The cluster is some 600 light years from us. It formed in a gas cloud about 700 million years ago.