What Is #29: The Pleiades Cluster

After recently discussing globular clusters and open clusters in this "What Is" series, let me talk briefly about a specific star cluster that is easy to see with the naked eye in the northern hemisphere, the Pleiades.

Pleiades star cluster - NASA, ESA, AURA/Caltech, Palomar Observatory The science team consists of: D. Soderblom and E. Nelan (STScI), F. Benedict and B. Arthur (U. Texas), and B. Jones (Lick Obs.)

The Pleiades is an open cluster of a few thousand stars with several very bright, blue stars that make it a very easily observed star cluster, even with the naked eye. It's best observable in the winter months in the northern hemisphere, and you can see it from part of the southern hemisphere, but if you get too far south it's always hidden by the horizon.

The Pleiades is a naked eye object for several reasons. One is the make up of stars. These very large, very blue stars emit a lot of light. On top of that, they are very close to Earth, at only 444 light years. This may seem a large distance, but in astronomical terms, 444 light years is very close given the Milky Way galaxy itself is approximately 100,000 light years in length.

The Pleiades is one of the top objects I have my students look at when we head outside in the late fall of the first semester. It's an easy object to find and very impressive through the telescope. You can see the mixture of stars and gas, along with the very bluish color. Very impressive!

These are young stars, with an age of around 100 million years. Much longer than the 75-85 year expected lifetime of a human, but very young when compared to the age of the Earth at 4.5 billion years old.

The next time you are outside in the evening, take a look up. Even if it is summer and the Pleiades are not up, something else that is just as cool is! Look up and enjoy the sights!