Messier Monday: A Great Galactic Controversy, M102

“Men... have had the vanity to pretend that the world creation was made for them, whilst in reality the whole creation does not suspect their existence.” -Camille Flammarion

Welcome to the latest -- and most controversial -- Messier Monday, where each week, I'll take a look at one of the 110 deep-sky objects that make up the Messier catalogue. These objects were identified so as not to be confused with potential comets, and make up the brightest and best-known observational sights beyond our own Solar System. But there is one object that, if you go to the wikipedia list, that has not been conclusively identified.

Image credit: SEDS Messier Catalogue, from; Box by me.

You will notice that there are two candidates -- that are two very different objects -- for what this galaxy is.

Image credit: SEDS Messier Catalogue, from

A little background first: you must realize that Charles Messier was not the first person to create a catalog of deep-sky objects. What was special about Messier's catalogue is twofold: it was both the first one to be almost 100% correct, whereas the other catalogues of the time had many errors as far as locations (or even existences) of the objects therein, and Messier's catalogue had a purpose, in that these objects were easily visible to an amateur with even a small telescope. It was smaller (at a total of 110 objects in its final form) than other contemporary catalogues (like William Herschel's), but it was so uniquely useful that it remains in use even today, hundreds of years after its completion.

The problem is, Messier's coworker (and co-compiler of the Messier Catalogue), Pierre Méchain, disavowed its existence, and claimed it was a duplicate of Messier 101, the well-known Pinwheel Galaxy. (Longtime readers may remember M101 from its spectacular supernova just a year ago, the closest supernova to us since 1987.)

Image credit: Reuters / BJ Fulton (Las Cumbres) and the Palomar Transient Factor.

But I think Méchain is wrong, and that Messier 102 is actually this spectacular object, also known as NGC 5866.

Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); W. Keel.

The controversy has existed for hundreds of years. Here's the problem. In his notes, this is what Messier wrote back in 1781:

102. Nebula between the stars Omicron Boötis and Iota Draconis: it is very faint, near it is a star of 6th magnitude.

Now, the constellations Boötes and Draco do, in fact, border each other. And the star Iota Draconis is, in fact, very close to the constellation Boötes, which is what you'd expect.

Image credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg).

The problem comes when we look for the star Omicron Boötis, which is over forty degrees away from Iota Draconis! This would make no sense to write down in a catalogue, and led Méchain to conclude that, in fact, this was just a duplicate observation of M101.

But there was another school of thought, and it wasn't put forth until 1917 by Camille Flammarion, that perhaps the greek Omicron that Messier wrote down (ο, below in red) was actually a lowercase greek Theta (θ), which would be located below in blue.

Image credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg).

If this were the case, then what you'd find was that, just above the edge of the handle of the Big Dipper would correspond to the location of a certain deep-sky object that sounds an awful lot like the M102 object that Charles Messier described.

Image credit: Me, created with the free software Stellarium,

At sufficiently north latitudes (this is from my location, Portland, OR about an hour after sunset), you can find this object even in tonight's wintery skies. To illustrate exactly where this is (and where the well-known M101 is relative to it), I've zoomed in just a little and labeled some of the key stars.

Image credit: Me, created with the free software Stellarium,

I think, based on this new information (which is still controversial), it's pretty incontrovertible that Messier 102 is, in fact, the same as NGC 5866, which means that you can find these spectacular views for yourself!

Image credit: Bob Austin of

This faint, edge on spiral galaxy has a spectacular dust lane running through its center; it's quite conceivable that this galaxy is somewhat similar to our own Milky Way as it would be viewed by a galactic outsider at just the right angle.

A nice, wide-field view of this galaxy is shown below.

Image credit: Paul and Liz Downing;

It looks very much like it's an edge-on spiral galaxy through a small, amateur telescope. But what would a professional telescope be able to see?

This galaxy has been imaged by the Sloan Digital Sky Survey, which shows not only the galactic disk, bulge, and central dust lane, but also the extended "halo" of stars that live well outside of the planar disk that dominates in smaller telescopes.

Image credit: Sloan Digital Sky Survey.

In other words, this isn't a spiral, but a Lenticular galaxy, or a galaxy that has both properties of a spiral and an elliptical.

Finally -- as is the case wherever it's available -- the most spectacular view of this galaxy is revealed by Hubble. Even background galaxies are visible through the glow of this mammoth, located "only" 45 million light-years away.

Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

And that's the story of Messier 102, perhaps the most controversial object in all of the Messier Catalogue!

Now that the mystery's been solved, and we know it's a giant lenticular galaxy (known as the Spindle Galaxy), feel free to take a look back at all our previous Messier Mondays:

Which Messier object will be highlighted next? Let's hear which one you want, and I'll make it happen. Happy Messier Monday!

More like this

Love the Hubble image.

By theTentman (not verified) on 17 Dec 2012 #permalink

Forgive my ignorance.
I would like to know whether we can "see" the formation of our galaxy and solar system if we're truly looking back at the origins of the Big Bang.
Is it possible to "see" back in time from the point that you are looking from and see yourself?
Or are we just looking "over there" at an event that occurred?
Is it possible to "see" the light from the formation of our galaxy?
If the light is only now reaching us from events that happened billions of years ago, can our system be in it and would we recognise it?
All of these questions may have already been answered, so once again, forgive my ignorance and please point me in the right direction.

"Messier’s catalogue had a purpose, in that these objects were easily visible to an amateur with even a small telescope"

Not actually correct. They were selected because Messier and many astronomers of the time were comet hunters and many sightings were found to be faulty because they were not comets but nebulous objects that could look a bit comet-like.

That's what the catalogue was for.

It's *used* nowadays as a good list of objects, but it is absolutely not the only one. Caldwell is a very modern version (Patrick Moore MBE, his wife was Caldwell). That was taken as a selection of the best objects for a northern lattitude observer (so misses out things like the Scutum/Scorpio nebulae).

M40 though was known to be a binary easily by the optics of Messier's day. It doesn't look the least bit comet-like. God knows why he included it, but he did.

The catalogue was a compilation of many people's work, they were all "gentlemen scholars" and freely shared their work. Messier for most of them merely confirmed their location before putting them in his catalogue.

"Forgive my ignorance.
I would like to know whether we can “see” the formation of our galaxy and solar system if we’re truly looking back at the origins of the Big Bang. Is it possible to “see” back in time from the point that you are looking from and see yourself?"

Nope, sorry. The reason is because to see yourself in the past, you'd have to intercept light from yourself in the past with your eyes (or telescope) today. But that light is long gone -- it was traveling away from you at the speed of light, while you are moving at a comparative stand-still.

That's why age and distance are related -- the light from an object 50 light years away was emitted 50 years ago, and that's the only age it can be.

The only way to see yourself in the past is for you to travel faster than light so that you can intercept the photons that you emitted long ago. But that would cause a whole host of other weirdness as well, if it were possible.

“Forgive my ignorance”

"Nope, sorry"

But isn't there a way to see the reflections or "light echos" from some objects such as those of Eta Carinae? Is it really just chance that those echos of Eta Carinae were found or is there a way to use that knowledge to find much older echos of the universe and perhaps see our own Galaxy? Would we even recognize it in its infant state much less recognize its current form. A feeling of apprehensive excited uneasiness would probably fill the heart as you looked at your own Galaxy millions of years in the past.

Hmm, I hadn't thought of reflections.

All we saw in the case of Eta Carinae was the light spectrum -- the cloud of gas the light was reflecting off of was far too irregular and diffuse to present an actual image of the star. It'd almost certainly be the same for a reflection of our galaxy since smooth mirrors rarely form naturally in space. So what we'd see would be the light spectrum of a young galaxy. Based on distance and location of the reflecting object, we might be able to deduce that the light we were seeing came from the Milky Way itself.

Which would be fascinating, and surely exciting, but I'm not sure why "apprehension" or "uneasiness" would come into play. Even if it was through some unlikely twist a full image of our young galaxy. I mean I don't feel that way when I see my old baby pictures.

I guess maybe if the primordial gas that would eventually form our galaxy happened to spell out "trolololol" or something I'd be kinda freaked...

In the case of SN1987A we had two sheets of gas cloud that were fairly thin and nearly parallel and perpendicular to the line from here to there.

We could see a ring (two rings from two sheets) but it wasn't an image by any stretch of the imagination.

A coherent image from a mirror will only occur if the plane through which the reflection is made is pretty damn thin. And it MUST be optically (if you're talking viewing visible light) thick.

Well that plain just doesn't happen.

An image from the light echoes is just never an option for anything.

It wouldn't even be anything like a galaxy either. If there were enough illumination from us to see anything in there, it would be a blob with each point smeared out by roughly one optical depth (thousands of light years? scores at least).

Moreover, for us to see the primordial milky way, it would have to be from an object about 7 billion light years away.

And the light intensity at that distance would be what...?

Heck, even if there was a great galactic mirror there, the image would be ~60x50,000/7,000,000,000 degrees across (~1.5 arc sec) and its intensity would be reduced as if we were looking at that object from 14 billion light years distance.

Except as said before, the light would be smeared out a lot because we don't have a galactic mirror in space.

A nice exercise for maths and BotE calculations.

Patrick Moore was never married. The Caldwell comes from his name which was Patrick Caldwell-Moore - he usually dropped the Caldwell but he used it for his list of objects.

By Chris Storey (not verified) on 18 Dec 2012 #permalink

You're right.

Mr Siegel, we owe you tremendously for these Messier Mondays ! Thank you..!

Count me also as NGC5866=M102.

By Eric Rachut M.D. (not verified) on 03 Apr 2015 #permalink