Jeweled Crosses

Reflecting on my previous posts, Just So Science has become a little complaining and angsty as of late, so without further ado here’s a return to something we can all agree on – our night skies are a treasure during winter!

Most people are familiar with the Southern Cross, or Crux, or ‘Te Punga’ (the anchor) to several Maori tribes, which hangs high in our southern skies at this time of the year, accompanied by the two bright pointer stars, Alpha and Beta Centauri that help you find it. (They’re often called the pointers because drawing a line between the points you to the real Southern cross). And if you ever forget the shape, you can always see it on our flag:

Just between Crux and the pointers lies a beautiful little open cluster of stars in the shape of a letter ‘A’ known as the Jewel Box or Jewel casket. These stars have all formed from the same original cloud of gas, but are all different sizes and temperatures so they all burn with quite notable different colours. There are about 100 stars in this cluster, each with its own unique hue, all appearing to be encapsulated within one dim star next to the Crux to the naked eye.

However, many people aren’t aware that our skies are actually graced by at two other ‘crosses’ that lie just next to the Southern cross in the Milky Way. Rather than true constellations, these two are ‘asterisms’  – patterns of stars that the eye readily picks out, that are unusually within larger constellations. The Diamond cross sits to the right of Crux (at early evening at this time of the year), and is defined by four bright points of light in the constellation on Carina. The False cross (which appears almost identical to the Crux, just dimmer and without the pointers) is outlined by 4 bright stars in the Vela constellation.  Together the constellations of Vela, Puppis and Carina (all just to the right of the cross) make up a vast boat from greek legend that soars throughout the milky way — the Argo, with the false and diamond crosses forming its two sails (it’s upside down relative to us in NZ as it was created in the northern hemisphere).

Why mention these now? These asterisms, when found allow you to find your way through one of the sparsely populated regions of the Milky way – yet this is also home to many of the treasures of our southern skies, the like of Eta Carina, the Carina and Keyhole nebula, one of the few naked eye Wolf-Rayet stars and NGC2516. I’ll show you how to find those in the next astronomy post – as their best viewing is coming up during the midst of winter.