Sunday, May 9, 2021

Exploring the constellation Pegasus


The bright winter constellations of the northern hemisphere are still a few hours away, but the October sky features the winged horse, Pegasus, with its familiar square, which forms the body of the horse.

The constellation Pegasus

The constellation is centered on the meridian (the line from Polaris to the southern horizon) at 9 PM on October 20. It’s only about 20 degrees of arc away from the North Star.

One of the stars in the Great Square of Pegasus is actually in the constellation Andromeda. That star is Alpha Andromedae, officially named Alpheratz, and is located 97 light years from the sun. It’s a binary star system; the brighter star is classified as B8 subgiant, a hot blue star.

A notable deep-sky object in Pegasus is Messier object 15 (M15). Near the star Enif, it has a magnitude of about 6.2 and might be visible to the naked eye or with binoculars if the sky is dark enough. It’s a globular cluster:

M15, the Great Pegasus Cluster (NASA, ESA via Creative Commons)

With a more powerful telescope, you’ll be able to see plenty of deep-sky objects in Pegasus, including several groups of galaxies, many of which are a mere 40 million light years from the sun. See the sky around Stephan’s Quintet, for instance.

The remaining stars in the Great Square of Pegasus are interesting as well. Scheat is a red giant, Markab a blue giant, and Algenib a blue subdwarf star.

Paul Katula
Paul Katula is the executive editor of the Voxitatis Research Foundation, which publishes this blog. For more information, see the About page.


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