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January 30, 2022

If you want a good test of both your eyes and your night sky, look high in the west this evening. If your eyes are sharp and your sky is clear and dark, you might just make out M33, the Triangulum Galaxy. It’s three million light-years away — perhaps the most-distant object visible to the unaided eye.

M33 is the third-largest member of the Local Group — the cluster of galaxies that includes the Milky Way. The Andromeda Galaxy is the largest member, with the Milky Way second.

M33 is roughly 60,000 light-years across — about half the size of the Milky Way. And it contains perhaps 10 percent as many stars as the Milky Way.

Like the Milky Way, M33 is a spiral galaxy. Beautiful spiral arms wrap around its heart. The arms are busy nurseries. They’re giving birth to stars at a faster rate than either the Milky Way or Andromeda.

M33 may be a satellite of Andromeda. And it’s possible that it’s made a close pass by the larger galaxy. If so, then M33 may someday merge with Andromeda, which in turn will merge with the Milky Way — creating a super-galaxy for the Local Group.

Look for M33 high in the west during the early evening. It’s about half way between two bright stars — Hamal to the left, and Mirach to the right. If you can’t see the galaxy with your eyes alone, it’s an easy target for binoculars — three million light-years away.

Script by Damond Benningfield

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