Looking Up: Pi in the Sky

Jan 9, 2017

Rich in star clusters and nebulae, the ancient constellation of Auriga, the Charioteer, rides high in northern winter night skies. Spanning nearly 24 full moons (12 degrees) on the sky, this deep telescopic mosaic view shows off some of Auriga's most popular sights for cosmic tourists. The crowded field sweeps along the plane of our Milky Way galaxy in the direction opposite the galactic center.
Credit mage Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors) / Nasa.gov

This week on Looking Up  Hal reminds us to wear our helmets and also chats about the Starfish Cluster, located in the constellation Auriga.  

In this safety-conscious age, it’s always wise to wear a helmet when riding a bike, skiing, or driving a chariot. So maybe it’s not surprising that high in the southern Colorado sky right now is the pointed helmet of a charioteer, the constellation Auriga (or-EYE-gah). 

This medium-size constellation contains the sixth brightest star in the sky, Capella, which we discussed back in November 2015.

Auriga is also interesting because it contains the galactic anti-center. In other words, when you look at Auriga, you are looking at the point in the sky directly opposite the center of our galaxy.

But Auriga also contains a very pretty group of stars known as the Starfish Cluster. One of three open clusters in Auriga, the Starfish Cluster is gorgeous through a small telescope or even binoculars. Such open clusters are often made up of newly formed stars. The stars in the Starfish Cluster are around 220 million years old, only about 5% as old as our own Sun.

At a distance of about 4200 light years, the Starfish Cluster isn’t exactly a next-door neighbor. Anyone located there would need a very good telescope to even see our own Sun, which would appear as a 15th magnitude star to them. Observers have noted that the cluster’s brightest stars form the rough shape of the Greek letter pi.

So, why is the Starfish Cluster called the Starfish Cluster? Because it looks like… well, not much! We don’t really know why the ancients called it the Starfish. It definitely doesn’t look like, well, anything other than a lovely collection of stars. So, take a look and see if you can figure out what the heck those old astronomers were talking about.

If you’d like to take a closer look at the Starfish Cluster, or any of the other wonderful and amazing things in the sky, please visit CSASTRO.org for a link to information on our monthly meetings and our free public star parties! 

This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado!