Image Credit & Copyright: Mega Prime Canada-France-Hawaii Telescope (CFHT) Corporation.
Sitting at the feet of the twins in the constellation Gemini are a beautifully contrasting pair of open star clusters. The beautiful blue hue of Messier 35 (M35) indicates young, vibrant stars, still in the glory of their youth while the visually smaller white-yellow cluster on NGC 2158 contains stars that have grown from youth and have entered into maturity.
All being told, these clusters aren’t side by side at all. They’re what you call line of sight open clusters and they don’t interact with one another at all. M35 is an open star cluster that resides 2,800 light years away and its constituents are a relatively young 100 million years old. NGC 2158 is yet another open star cluster but it sits a much more distant 11,200 light years away with stars well over a billion years old.
What’s an Open Star Cluster?: Well, the process isn’t too far off the basic foundation of how individual stars themselves are formed. It all starts when mommy and….my apologies, wrong story. It all starts when a molecular cloud, usually molecular hydrogen and other relatively light elements becomes dense enough to where the cloud rapidly collapses under its own gravity. The ensuing pressures and temperatures within the compressing cloud, generates conditions suitable for rapid, mass star formation to occur. Depending on the size and makeup of the cloud, this process can generate anywhere from tens to hundreds to thousands of stars.
After formation, these newborn stars push away most the remaining molecular cloud that created them via massive stellar winds (radiation pressure) and in time, they themselves will slowly drift apart as they age, get jobs and……my apologies again, I get sidetracked. But yes, they will drift apart over time just as the stars of the Big Dipper have done and the stars of the Pleiades are slowly in the process of doing. This process of stars migrating apart from one another is partly from the gravity of other members of the group, interactions with other nearby clusters and the gravity of nearby molecular clouds. Unlike globular star clusters, stars within open clusters will typically long outlive the cluster and become independent stars traveling the universe.
Their appearance can vary greatly depending on the stars themselves, how many there are in the group, their surroundings etc. Some are so widely spaced that you barely recognize them as a cluster at all such as the asterism of the Big Dipper, while others are often misidentified for globular star clusters such as NGC 411. Many different factors conspire to give an open cluster its appearance. To date, more than 1000 open star clusters have been identified and cataloged in the Milky Way. They are also a commodity as they are all relatively similar in age, astronomers can use that to closely study stellar evolution in as controlled an environment as they can find.
Can’t get enough of these? Look below for some earlier posts I created on open clusters or ht the “Star Clusters (Globular-Open)” category at the right of the page.
NAME: The bright blue cluster in Messier 35, M35 or NGC 2168 and the dim yellow cluster is New General Catalog 2158 or NGC 2158.
WHAT IS IT?: Two line of sight open star clusters.
HOW FAR AWAY IS IT?: M35 is roughly 2,800 light years away and NGC 2158 is 11,200 light years distant.
HOW BIG IS IT?: Entirety of the image is 60’ x 60’ or 1 square degree of night sky.
APPARENT MAGNITUDE: M35 is a bright 5.2 while NGC 2158 is a dim 8.5.
WHERE IS IT? (General): Constellation Gemini (The Twins).
WHRE IS IT? (Exact RA/DEC J2000): RA 06h 09.1m / DEC +24° 21′.
CFHT release for this image: http://www.cfht.hawaii.edu/News/MegaPrime/MegaPrime-PR-AstroImage-M35NGC2158.html
More Open Cluster Madness:
Rosette 3 Image Zoom: https://danspace77.com/2015/02/06/the-rosette-nubula-3-image-zoom/