Download Winter constellations

Winter constellations
December evenings are a great time to see the wonderful winter constellation of Orion,
Taurus, Sirius and the Pleiades. Orion, the Hunter (to the medieval Arab astronomers,
the Giant), with the triplets of stars of his belt and sword, and to the upper left the bright
red star Betelgeuse. The name means ‘arm of the giant’ in Arabic and it is a red
supergiant star about twenty times the mass of the sun. The bottom ‘star’ of Orion’s
sword appears slightly fuzzy to the naked eye and is the Orion Nebula, number 42 in
Charles Messier’s famous list of nebulae of 1759, part of a cloud of gas and dust where
new stars are forming.
Following the line of Orion’s belt towards the upper right from Orion we reach the V of
Taurus, the Bull, with another prominent red star, Aldebaran, making up the eye of the
Bull. The Taurus constellation looks particularly brilliant with binoculars, glittering with
young blue stars. Aldebaran is a red supergiant star and is about five times the mass of
the sun. The name means ‘follower’ because it follows the Pleiades, the Seven Sisters,
which are located on the other side of Taurus from Orion. With the naked eye you should
be able to make out 6 or 7 stars in the Pleiades, which is a cluster of young stars ‘only’
about 50 million years old. With a telescope hundreds of stars become visible. At the
moment Jupiter is sitting in the constellation of Taurus, dazzlingly bright.
To the lower left of Orion is the bright star Sirius, the Dog Star, which generally appears
white or blue, but can take other colours when it is close to the horizon. Sirius lies in the
small constellation of Canis Major, the Great Dog, which is meant to be Orion’s dog. It
is the brightest star in the sky and is a hot giant star just over twice the mass of the sun,
and over twenty times as luminous as the sun. The tradition that Sirius’s rising with the
sun in July and August caused fever, the Dog Days, lasted from Greek and Roman times
through to the eighteenth century.
The Infrared Astronomical Satellite, IRAS, which surveyed the sky at infrared
wavelengths in 1983, showed us that the whole Orion constellation is covered with giant
clouds of gas and dust, with many deeply embedded newly formed stars visible only at
infrared wavelengths.
Past Stars’n Tides articles can be found at http://astro.ic.ac.uk/~mrr/starsntides/