The Evening Sky in December 2017

Download a PDF containing this chart, additional charts for specific areas of the sky and descriptions of interesting objects visible at this time of year.

The Evening Sky in December 2017

The brightest stars are in the east and south. Sirius, the brightest of all the stars, is due east at dusk, often twinkling like a diamond. Left of it is the bright constellation of Orion. The line of three stars makes Orion's belt in the classical constellation. To southern hemisphere skywatchers they make the bottom of 'The Pot'. The faint line of stars above the bright three is the Pot's handle or Orion's sword. At its centre is the Orion Nebula, a glowing gas cloud nicely seen in binoculars. Rigel, directly above the line of three stars, is a hot blue-giant star 770 light years* away. Orange Betelgeuse, below the line of three, is a cooler red-giant star 430 light years away.

Mercury and Saturn (not on the chart) are low in the southwest twilight at the beginning of the month, right of the Scorpion's tail, setting 80 minutes after the Sun. Mercury is above Saturn and slightly brighter at first, but fades and sinks toward Saturn. The two appear close together on the 7th. After that Mercury quickly disappears into the twilight with Saturn slowly following.

Left of Orion is a triangular group making the upside down face of Taurus the bull. Orange Aldebaran, at one tip of the V shape, is one eye of Taurus. The stars on and around the V, except for Aldebaran, are the Hyades cluster. It is 150 light years away. Aldebaran is not a member of the cluster. It just happens to be on the line-of-sight at about half the cluster's distance. Further left is the Pleiades/Matariki/Subaru cluster, a tight grouping of six naked-eye stars impressive in binoculars. It is 440 light years away.

Canopus, the second brightest star, is high in the southeast. Low in the south are the Pointers, Beta and Alpha Centauri, and Crux the Southern Cross upside down at this time of the year. In some Maori star lore the bright southern Milky Way makes the canoe of Maui with Crux being the canoe's anchor hanging off the side. In this picture the Scorpion's tail, just setting, can be the canoe's prow and the Clouds of Magellan are the sails.

The Milky Way is wrapped around the horizon. The broadest part is in Sagittarius low in the west at dusk. It narrows toward Crux in the south and becomes faint in the east 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 thick hub or central bulge of the galaxy, 30 000 light years away, is in Sagittarius. The nearby outer edge is the faint part of the Milky Way below Orion. A scan along the Milky Way with binoculars finds many clusters of stars and a few glowing gas clouds.

The Clouds of Magellan, LMC and SMC, high in the southern sky, are two small galaxies about 160 000 and 200 000 light years away, respectively. They are easily seen by eye on a dark moonless night. The larger cloud is about 1/20th the mass of the Milky Way galaxy, the smaller cloud 1/30th but that is still many billions of stars in each.

Very low in the north is the Andromeda Galaxy seen in binoculars in a dark sky as a spindle of light. It is a bit bigger than our Milky Way galaxy and nearly three million light years away.

Mars, Jupiter and later Mercury appear in the eastern dawn sky. On the 1st reddish Mars rises due east after 3:30, appearing below the blue-white star Spica. Golden Jupiter is the brightest 'star' in the morning sky, rising around 4:30. By mid-month Spica, Mars and Jupiter appear equally spaced along a diagonal line. By the 31st Jupiter is low in the east at 3 a.m. with Mars, much fainter, above and left of it. Mercury begins a rapid ascent of the dawn sky in the last third of December after passing between us and Sun. By the 23rd it will be rising an hour before the Sun, appearing directly below orange Antares, a position it holds till the end of the month.

*A light year (l.y.)is the distance that light travels in one year: nearly 10 million million 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.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
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