Wednesday, October 20, 2021

The Southern Cross rises again




By Mike P. Usher 

May and June is the time of year when the most interesting objects in the very deep southern sky pop above the horizon for a few hours. First and foremost is the Southern Cross, technically named Crux. It is always a challenge to see the bottom star, Acrux, but the northernmost three are easy given a clear sky and a flat southern horizon. For this the best spot to be is a beach with a southern view. In terms of area Crux is the smallest full constellation in the sky, but there are asterisms such as the Pleiades which are smaller. Curiously the same optical illusion which makes the full Moon look so much larger when near the horizon seems also to work on Crux. Tonight Crux is the highest just before 11 PM so you might wish to wait until then to look for it. Alternatively you could wait for the first week of June to see it at 9 PM – but it is a risk; the closer it is to rainy season the cloudier the evening sky becomes (and brighter due to the late sunset). These are the primary reasons so few people on Marco have seen the cross.

Binoculars are very handy to have when scanning the southernmost sky, this area is thick with star clusters and other items of interest. Also binoculars help to penetrate the murk that always lies along the horizon. The most important thing to look for is the giant globular cluster Omega Centauri, marked with a “w” on the map. It is so bright (magnitude 3.7) it is even visible with the naked eye as a faint smudge in the constellation Centaurus. In binoculars it blossoms into a bright fuzz ball roughly the apparent size of the full Moon. There are approximately one million stars in Omega Centauri, but I’m not sure anyone has been able to count them all. Certainly there are no less than 500,000. Omega Centauri is so large in fact there has been some speculation in recent years that it is actually the core of a small galaxy that the Milky Way has cannibalized in the remote past.

As long as you have binoculars in hand, scan the whole southern Milky Way for interesting objects. The whole area is thick with star clusters and nebulas, particularly in the region of Carina.

See you next time! 

Mr. Usher is President of the Everglades Astronomical Society which meets every second Tuesday at 7:00PM at the Norris Center, Cambier Park, Naples. 

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