What's Up in Space
This Weekend’s Night Sky (28-29 March 2015)
Saturn is in the constellation of Scorpius, a little below and to the left of the bright star Antares and is fast becoming a must see evening object. It is now rising just before 10pm, but by the end of April it will be above the horizon before twilight ends.
Above Saturn, and high in the east after dark is the constellation of Centaurus, with the two brightest stars, Alpha and Beta Centauri, pointing to Crux, the Southern Cross.
The constellation contains a number of interesting star clusters and nebulae.
The globular cluster ω Centauri is perhaps the most famous, and is easily visible to the naked eye at magnitude 3.7. This is by far the largest and brightest globular cluster in the Milky Way, with a luminosity greater than a million Suns.
ω Centauri measures around 150 light years across and contains several million mainly yellow dwarf stars. As with most globular clusters these stars are incredibly old, with an average age of 12 billion years.
The cluster is relatively easy to find even with the naked eye, appearing as a fuzzy star around 13 degrees north east of Gamma Crucis at the top of the Southern Cross. In fact it was originally thought to be a star and was given the Bayer designation Omega as the 24th brightest in the constellation. Unaided it appears to cover around half a degree when seen from a dark, rural location. Through binoculars it is an even more stunning sight, spanning almost a full degree of the sky, twice that of the full moon.
With a small telescope the cluster becomes a glowing, shimmering ball of stars, with many individual stars visible towards the outskirts of the cluster.