Physics Photo of the Week

Physics Photo of the Week

November 22, 2024

Galaxy M33 - The Triangulum Galaxy

The Triangulum Galaxy (M 33) is located in the Triangulum constellation fairly close to the more famous Andromeda Galaxy in the sky, and is about the same distance from the Earth (between 2 million and 3 million light years).  The Triangulum Galaxy,  is smaller (less massive) and fainter than the Andromeda Galaxy, but it appears more delicate and seems to show more discete clouds of stars and a number of large clusters in its spiral arms.  

At right is a photo of the Andromeda Galaxy, but taken with a smaller focal length telescope.  The Andromeda galaxy covers a much larger proportion of the sky (about 3 degrees across) compared with the angular size of the Triangulum galaxy (about 1/3 degree across).  Short focal length telescopes show a larger field of view than long focal length telescopes, hence the Andromeda appears smaller than the Triangulum in these telephotos.  The Andromeda galaxy is accompanied by neighboring smaller elliptical galaxies (the "blobs" to the right center and the lower corner of the Andromeda's photo.  The actual size of the Triangulum is slightly larger than either of the elliptical galaxies.  

Galaxies are the largest and most massive discrete objects known.  The Andromeda and our own Milky Way galaxy contain about 1 trillion stars (1012) each.  The Triangulum galaxy "only" about  40 billion stars (40 x 109).

The angle of the disks of the two galaxies relative to our line of sight is the orientation angle.  The face of the Triangulum's spiral is approximately face-on in the direction of line of sight, whereas the orientation of the larger Andromeda Galaxy is about 50 degrees away from "face-on".  Thus the shape of the Andromeda Galaxy resembles a Frisbee toy in flight.

These two galaxies (the two closest external galaxies to the Milky Way) are only two of the estimated 1 trillion (1012) galaxies in the universe - as evidence from deep sky photos from the Hubble and James Webb space telescopes.

Much astronomical research has been done observing these two "close" galaxies.  References may be found in Wikepedia.

Both photos were made by Donald Collins at the College View Observatory.

These two galaxies' locations in the Sky are shown in the partial sky map below as M31 and M33 in the constellations Andromeda and Triangulum:



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Physics Photo of the Week is published periodically during the academic year on Fridays by Donald F. Collins, professor emeritus of Warren Wilson College. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

To join the mailing list, please request to Donald Collins at the e-mail address below.  You will receive no more than one message every two weeks, or when a very interesting physics/astronomy event is happening.

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