The Night Sky

November / December

The summer stars have all now set in the west; soon Orion will dominate the winter sky to the south. But in the meantime...

This month’s highlights start in the south, in the constellation of Pegasus – why not visit a (tiny) bit of astronomical history by giving 51 Pegasi a quick look? 51 Pegasi (abbreviated 51 Peg), also named Helvetios, is a Sun-like star located 50.9 light-years from Earth. It was the first main-sequence star found to have an exo-planet (designated 51 Pegasi b, unofficially dubbed Bellerophon, later named Dimidium) orbiting it.

Night Sky - December

On October 6, 1995, Swiss astronomers Michel Mayor and Didier Queloz announced the discovery of an exo-planet orbiting 51 Pegasi. The discovery was made with the radial velocity method on a telescope at Observatoire de Haute-Provence in France and using the ELODIE spectrograph. At a magnitude of +5.45 this requires binoculars or a small telescope, but give it a quick look. It may not be very exciting to look at but it does have its own little place in history.

While in the area, have a look at the Andromeda Galaxy (M31) – navigate to this from the larger of the two ‘V’s that make up Cassiopeia to the brightest star in the constellation of Andromeda and work your way upwards. The same distance beneath Andromeda is the Triangulum Galaxy (M33) – at 3 million light years distance, this is the furthest object (barely) visible to the naked eye (but you will need a very dark night !).

NGC-457 Navigate to NGC457 (the Dragonfly Cluster) from the two east-most stars in Cassiopeia – come west about half the distance between the stars and down a fraction. The cluster is sometimes referred to as the Owl Cluster, Kachina Doll Cluster, the ET Cluster (due to its resemblance to the movie character) or the "Skiing Cluster". Two bright stars, magnitudes 5 and 7 can be imagined as eyes. The cluster features a rich field of about 150 stars of magnitudes 12-15.

Finish by having a look at Mesarthim in Aries – a very pretty double star.
Other double stars in the night sky this month which are worth a look are:

Mintaka is easy to locate, as it is the westernmost of the three bright stars making up Orion's belt. It is actually a complex multiple system, but can be seen with a small telescope as a binary star with one star much brighter than the other.

Epsilon Pegasi, known as the 'pendulum star' This double star forms the 'nose' of the Pegasus constellation. There's an optical illusion associated with this double star, noted many years ago by the famous astronomer Sir John Herschel; if the telescope is moved whilst the double star is being observed, the fainter star seems to swing relative to the brighter one. The brighter star often appears as bright orange in colourand is otherwise known as Enif.

Eta Cassiopeiae - this one needs a good telescope to be seen properly, but the colours are worth looking out for - they appear as bright yellow and red. This double star is in the constellation Cassiopeia, which is one of the most distinctive features of the winter sky. This binary is also known as Achird. 

Zeta Aquarii in Aquarius, where it forms part of the 'water jar'. This one is difficult to see without a good telescope, but it has a lovely clear blue-white colour. The gap between the two component stars is slowly widening.

(You will probably need Stellarium to locate these stars).

Meteor Showers

December plays host to two meteor showers - the Geminids are an annual meteor shower caused by the 3200 Phaethon asteroid. The meteor shower peaks on December 14th.

Geminid Meteors

The Ursids meteor shower peaks on the night of December 22nd. The shower is named the Ursids because the meteors seem to radiate from the direction of the constellation Ursa Minor in the sky.
The Ursids are associated with the comet, 8P/Tuttle, also sometimes known as Mechain-Tuttle's Comet.

In January, the first major shower of the year, the Quadrantids, will peak on the night of January 3rd.

Night Sky - December Meanwhile, in the east, the constellation of Taurus (the Bull) has risen. The open cluster, M45, the Pleiades (often called the Seven Sisters), it is one of the brightest and closest open clusters and will richly repay a visit with binoculars. In a small telescope, the brightest stars can be seen surrounded by blue reflection nebulae caused by reflected light from many small carbon grains.

Also in Taurus is the Crab Nebula (M1 is the first entry of Charles Messier's catalogue). Lying 6500 light years from the Sun, it is the remains of a giant star that was seen to explode as a supernova in the year 1056. It may just be glimpsed with binoculars on a very clear dark night and a telescope will show it as a misty blur of light.

Later in the night, the majestic constellation of Orion will dominate the sky to the south. As well as being home to both the Orion and Horsehead nebulae, Orion is a wonderful ‘guide post’ constellation, pointing the way to neighbouring constellation all winter.

A line through Orion’s belt leads to Sirius in Canis Major to the south-east; in the opposite direction it leads to Aldebaran in Taurus. A line from Rigel through Betelgeuse leads to Castor and Pollux in Gemini.

Night Sky - December

The Orion Nebula is easy to find and always wonderful to see in the telescope – the Horsehead Nebula is an extremely challenging visual target.