Star clusters from my balcony observatory

Two star clusters from my balcony. Messier 46 is the fainter cluster in the lower center. Messier 47 is the brighter cluster in the upper center. Credit: Chris Casper

Two star clusters from my balcony. Messier 46 is the fainter cluster in the lower center. Messier 47 is the brighter cluster in the upper center. Credit: Chris Casper

This is a picture I took from my balcony last night of two open star clusters Messier 46 and Messier 47. It’s the latest effort in my on-again-off-again dabbling with the hobby of astrophotography. The picture won’t win any awards but it does show what you can do with limited equipment - and skill. 

The stars in M46 and M47 are galactic youngsters by comparison to the Sun. The 500 stars in M46 formed about 300 million years ago. At that time giant amphibians ruled an Earth covered in forests that we would eventually mine as coal. The 50 stars in M47 formed 78 million years ago - around the time an asteroid was wiping out the dinosaurs.

The European Southern Observatory created this image of Messier 46 (on the left) and Messier 47 (on the right) using data from the Digitized Sky Survey 2. Credit: ESO/Digitized Sky Survey 2 Acknowledgement: Davide De Martin

The European Southern Observatory created this image of Messier 46 (on the left) and Messier 47 (on the right) using data from the Digitized Sky Survey 2. Credit: ESO/Digitized Sky Survey 2 Acknowledgement: Davide De Martin

The UK Schmidt Telescope Credit: AAO

The UK Schmidt Telescope Credit: AAO

The ESO's picture looks a lot better than mine - that’s where equipment and skill come in. Their data came from the UK Schmidt Telescope. With a diameter of 1.2 meters, it has more than 400 times the light-gathering ability as my little telephoto lens. Research-grade sensors and a dark, mountain-top location in southeastern Australia are just some of the many other reasons I can’t make pictures like that.

By comparison, I am using an older DSLR camera, a Canon 550D/T2i, connected to a 300mm zoom lens with a maximum diameter of 58mm. My balcony location under the light-polluted Southern Californian skies has the added bonus of a sodium streetlight:

There's so much wrong with my balcony observatory. It's a wonder I can get any pictures at all. Credit: Chris Casper (go ahead make this your desktop background - I double dog dare you)

There's so much wrong with my balcony observatory. It's a wonder I can get any pictures at all. Credit: Chris Casper (go ahead make this your desktop background - I double dog dare you)

The challenges of balcony astronomy notwithstanding, I can take reasonable pictures of the brighter objects in the night sky. I won't win any awards, but it gets me learning about the objects themselves.

Star clusters are important tools for understanding how stars work and how they change over time. Astronomers maintain catalogs listing hundreds of the Milky Way’s observable star clusters - only a fraction of the thousands astronomers believe exist throughout our galaxy. Clusters are such valuable research subjects that astronomers don’t limit themselves to clusters in the Milky Way. The Andromeda Project, for example, mapped over 2,700 star clusters in the Andromeda Galaxy with the help of 30,000 citizen scientists. You can read a preprint of the paper introducing the catalog to the astronomy community (arXiv: 1501.04966).

Star clusters emerge from the vast molecular clouds of gas and dust that orbit throughout the Milky Way. A denser pocket of gas within a cloud will exert a greater gravitational pull on the surrounding gas and start gathering it in. The gas at the center of the pocket compresses until the pressure supports nuclear fusion - a star is born. 

But it won’t be alone. Star formation happens in a rush as hundreds to thousands of newly born stars roil the surrounding cloud. The stars eventually tear the cloud apart, bringing star formation to a stop and leaving the cluster of stars to orbit the galaxy in formation. Over the course of the next few hundred million years the stars drift apart to blend into the billions of other stars in the galaxy. The Sun once belonged to a star cluster, but it drifted away over the past 4.5 billion years.