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Messier Monday: Messier’s Final Galaxy, M110

The last object in the entire Messier Catalogue is faint, elusive, and the most common type of galaxy in the Universe!

Image credit: Adam Block / NOAO / AURA / NSF, via RC Optical Systems.

“The human mind is capable of excitement without the application of gross and violent stimulants; and he must have a very faint perception of its beauty and dignity who does not know this.” –William Wordsworth

There are plenty of bright, extended objects in the night sky, clearly distinct from the stars and planets. While a few of them happen to be comets or asteroids within our own Solar System, the vast majority are star clusters, nebulae and galaxies ranging from a few hundred to many billions of light years away. The first large, accurate and verifiable catalogue of these deep sky objects was the Messier Catalogue, consisting of 110 objects. Although Messier himself didn’t know about our modern categories, it turns out that a whopping forty of these objects are galaxies, more than any other type.

Image credit: Tenho Tuomi of Tuomi Observatory, via

Most of the galaxies that he found were nearby, bright giant galaxies: some spirals and some ellipticals, with the majority of them larger and more massive than our own Milky Way. But a few of these galaxies are much harder to find: smaller, fainter, lower in mass and much more compact. Although he never would have known it, they’re the most common type of galaxy in the entire Universe, and the very last object in his entire catalogue, Messier 110, is perhaps the best example of them.

Here’s how to find it in tonight’s sky.

Image credit: me, using the free software Stellarium, via

After sunset, the sky will darken, and then even moreso a hour or so later when the Moon sets. In the north, Polaris (the North Star) will be flanked, as it always is, by the Big Dipper on one side and by the great “W” of Cassiopeia on the other. And if you look beneath the bottom of the “W”, you’ll find a row of four bright stars: Mirphak, Almaak, Mirach and Alpheratz. Look to Mirach — β Andromedae — the third of these, to guide you towards Messier 110.

Image credit: me, using the free software Stellarium, via

Directly “above” it, or back towards the “W”, you’ll find one star that stands out just a handful of degrees away: μ Andromedae, clearly visible to the naked eye even with the Moon out. About the same distance away, roughly along the same line, you’ll come to ν Andromedae, a magnitude dimmer but still not too difficult to find. And right above that star, you’ll come to the great nebula in Andromeda, M31, the Andromeda Galaxy.

Image credit: me, using the free software Stellarium, via

Don’t stop there, though! Continue upwards a little further — on the opposite side from ν Andromedae — and you’ll find a much smaller fuzzy object, visible only through a telescope. That’s Messier 110. Recorded the night Charles Messier sketched the great nebula in 1773, he gave the account of its discovery in 1801:

On August 10, [1773,] I examined, under a very good sky, the beautiful nebula of the girdle of Andromeda, with my achromatic refractor, which I had made to magnify 68 times […] I saw that which C. Legentil discovered on October 29, 1749 [Messier 32]. I also saw a new, fainter one, placed north of the great [nebula], which was distant from it about 35′ in right ascension and 24′ in declination. It appeared to me amazing that this faint nebula has escaped the astronomers and myself, since the discovery of the great [nebula] by Simon Marius in 1612, because when observing the great [nebula], the small is located in the same field of the telescope. I will give a drawing of that remarkable nebula in the girdle of Andromeda, with the two small [nebulae] which accompany it.

With modern equipment, it’s easy to spot with the unaided eyeball through a telescope.

Image credit: Jim M., via

And with a good amateur telescope and some quality astrophotography equipment, you can discover that it’s much more than an ellipsoidal fuzzball, but rather its own island Universe!

Image credit: Sid Leach, via

It wasn’t the final object discovered in the Messier catalogue, but the final one added, as that decision was only made in 1967. A good thing, too, because it not only totally belongs (having been discovered and catalogued by Messier), but it teaches us something new about the Universe that no other Messier object does.

As it turns out, Messier 110 is the only dwarf spheroidal galaxy in the entire Messier catalogue, and was most likely only discovered because of its proximity to its much larger neighbor. This is no coincidence, mind you, as this object is in fact a gravitationally bound satellite of its larger neighbor! At present, it’s located around 2,700,000 light-years from us, with an estimated distance of a few hundred thousand light-years from Messier 31.

Image credit: Canada-France-Hawaii telescope using the CFH12K camera.

In fact, the discovery of this object was our first clue to the true nature of how galaxies cluster together: not only in groups of large spirals (like our Milky Way, M31 and M33) that can grow into ellipticals after major mergers, but full of smaller, irregular galaxies that eventually cluster around and merge with the larger galaxies themselves! At a later date, it was recognized that the Magellanic Clouds — not visible from Messier’s location far in the nouthern hemisphere — were satellites of our own Milky Way galaxy. At present we now know there to be not only the three large spiral galaxies in our local group, but some forty dwarf galaxies of various sizes and in various stages of their lives! Messier 110 (NGC 205) is just one of them that happens to be relatively easy to find.

Image credit: © 2005 Cetin BAL.

Why is that? In addition to being both close to and well-separated from Andromeda, it’s actually on the larger side of these dwarf galaxies, containing an estimated four-to-fifteen billion solar masses of material, with over a billion stars inside!

Image credit: John Brady of Astronomy Central, via

It’s also remarkable for another reason: most small, satellite galaxies have their interstellar gas stripped away by gravitational encounters with their larger neighbors. But Messier 110 still has a large amount of its gas intact, as evidenced by multiple populations of young, blue stars, evidence that it’s undergone star formation very recently. The youngest stars in there formed just 25 million years ago, with the formation most likely catalyzed by periodic encounters with the Andromeda galaxy!

Image credit: Digitized Sky Survey (DSS).

It also has dust, which is visible due to its light-blocking effects in the visible, but which becomes transparent at infrared wavelengths.

Image credit: 2-micron all-sky survey (2MASS), via IPAC / University of Massachusetts / Caltech.

This galaxy is highly elliptical, and in a very rare occurrence for a galaxy this small, it has its own system of globular clusters, with eight identified so far.

Image credit: Victoria Brown, Christine Churchill, & Mike Dickerson, via

It also is being clearly disrupted by its giant neighbor, as streams of gas are being pulled out of the galaxy, something we only discovered recently thanks to the Isaac Newton Telescope, but which can be verified with the right wavelengths in the optical as well!.

Images credit: Isaac Newton Telescope (L); Wolfgang Paech via (R).

Finally, the most spectacular image available of this galaxy comes not from Hubble — even though the data exists — since it’s never been professionally processed. There’s a pretty good one from the Sloan Digital Sky Survey:

Image credit: Sloan Digital Sky Survey / Courtney Seligman, original via

But even that’s not the best. Remember, this isn’t the brightest, biggest, or closest galaxy to us, but it is the most common type of galaxy in the Universe — some ten times as common as a spiral like us — and we should consider ourselves luck to have an example waiting for us at the end of the Messier catalogue. And the greatest tour through this galaxy comes courtesy of amateur astronomer extraordinaire Jim Misti, whose 32″ telescope captured the following spectacular image:

Image credit: Jim Misti of Misti Mountain Observatory, via

You can even see a distant background galaxy through this dwarf galaxy at the bottom of the image. And with that, we come to the final object and the final galaxy of the Messier catalogue. We’ve only got four objects left, so enjoy your tour through the other 105 that we’ve covered here:

Travel the Universe with astrophysicist Ethan Siegel. Subscribers will get the newsletter every Saturday. All aboard!

Come back next week for a view of a brilliant cluster, as we enter the final month of Messier Monday here on Starts With A Bang!

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