Heh heh, sorry, not sorry for the bad pun. It’s what I do.
After looking at the moon and the same old planets for a short while, beginners quickly ask, “What else should I look for?” The answer is the Messier Catalogue.
I first came across Messier as a kid when I asked the very same question: “What’s next?” Back in the 70s, the answer to that question wasn’t Turn Left at Orion or Nightwatch or The Backyard Astronomer, but The Messier Album, by Mallas and Kreimer. When I got back into astronomy again three years ago after a 30-year layoff, I bought a used copy from Amazon to take a walk down memory lane. It’s still a useful resource.
This post isn’t a listing of the objects, with pictures and descriptions, what they look like through a scope, how hard they are to find, etc. That’s been done, and done excellently. And you should definitely go check that out. Besides, I’ve only seen about 65 of them, so why would you listen to me about them anyway? This post is about the man and his list.
Messier’s Early Life
Apparently, Messier was not very messy at all. Or at least, that’s what Mrs. Messier told a reporter from the National Enquirer one afternoon. “He certainly was no Oscar Madison,” she reportedly said. Okay, enough with the bad jokes. No, Charles Messier (properly pronounced “mess-ee-ay”) was a French astronomer from the 18th century who hunted comets. He was a prodigious discoverer of them, finding 20 in his lifetime.
King Louis XV of France nicknamed him the “Ferret of Comets”. This was back in the day when the general public – including royalty – still thought that comets were omens – portents of the future, whether for good or ill – although that position was rapidly changing for those in the field of astronomy. If you wanted to make your name as an astronomer back then, you had to get in the game by discovering comets. Non-moving objects didn’t matter; moving comets were where it was at. Messier had quite the talent for it. But Messier’s comets have been lost to the mists of time. It’s his Catalogue that lives on amongst amateur astronomers everywhere.
Born in 1730, orphaned at 11, Messier’s interest in astronomy was sparked by his seeing the six-tailed comet of 1744, when he was 14, and then the partial solar eclipse of 1748. This just shows, ya gotta get ’em interested in astronomy while they’re young. In 1751 he travelled to Paris and fell in with Joseph Nicolas Delisle, the Astronomer of the French Navy, who needed an assistant. Messier’s handwriting wasn’t messy at all, so he got the job.
I’m not completely kidding there. Okay, I am mostly; but he was hired as a recorder for Delisle. That meant that as Delisle was viewing through the eyepiece, he would describe what he was seeing. As recorder, Messier would write this down while also making note of the time and exact position of the object in the sky, and in reference to the positions of known stars. And, well, you have to have nice handwriting to do that. Within two years, Messier was making his own observations from the Marine Observatory at the Hotel de Cluny in Paris, including the 1753 Transit of Mercury.
In 1758, something important was to happen – the predicted return of Halley’s Comet. This was the first return of the comet since Halley had made his prediction that it would return. Up until that point, the thinking was that comets were one-off affairs – each one came by once, then left, never to be seen again. Halley hypothesized that the comets of 1682, 1607, and 1531 were all the same comet. Based on recorded observations and using Newton’s gravitational formula, Halley computed the comet’s orbit and its return in 1758. This was the first time anything other than the six known planets was recognized as orbiting the sun.
Halley’s Comet was “rediscovered” by a German gentleman astronomer named Palitzsch that Christmas, 1758, but the news of the discovery didn’t reach France for months. While looking for Halley’s Comet, and eventually finding it, Messier found a different comet. He also found an object in the constellation Taurus that looked like a comet, but didn’t move. Messier had just discovered (rediscovered, actually – it had been first been discovered in 1731) what we would later call the Crab Nebula, a supernova remnant.
To continue in his efforts to discover comets, Messier had to be meticulous in his observations. Finding the Crab Nebula made him decide to prepare a catalogue to make it easier to avoid such “nebulous objects” that would only turn out not to be comets. The Crab became M1 in his Catalogue, and Messier eventually replaced Delisle to become the Astronomer of the French Navy himself.
And just what was Messier’s Catalogue? Why, it was a list of objects with a nebulous character to AVOID observing while hunting for comets. Oh, the sweet irony! Poor Messier. Because what most amateurs do now is the exact opposite; we seek out and observe the Messier objects. So Messier’s name lives on forever with astronomers for precisely the opposite reason that he intended.
Messier published the Catalogue in two installments; the first in 1774, which included objects M1 to M45; and the second, objects M46 to M103, in 1781. But the Messier Catalogue is 109 – or 110 – items. What about the others at the end? As interest in his Catalogue resurfaced over the course of the 20th century, researchers reviewed his notes and found that Messier and his assistant/colleague, Pierre Mechain, had discovered 7 additional objects that Messier had not included in his published lists. It took a few decades, but they eventually got the number up to 110.
The Messier Catalogue consists of 40 galaxies, 29 globular clusters, 26 open clusters, 7 diffuse nebula, 4 planetary nebula, and 1 supernova remnant . . . and 4 mistakes. Notably, Messier didn’t discover all the items on his list. He collected previously discovered DSOs to put in the list; and his assistant, Mechain, was pretty good at finding these nebulous objects as well. Messier discovered 40 on the list; Mechain discovered 27; Messier included the others on his list to make it more comprehensive.
The objects go down to 10th magnitude. The 14 dimmest objects are dimmer than magnitude 9.5. All of these are galaxies, with the exception of M97 at 9.9, which is a planetary nebula called the Owl Nebula, because it appears to have two large eyes. I haven’t seen any of these “dim 14” yet.
The objects also go as bright as magnitude 1.6, which is the integrated brightness of all of the stars in the Pleiades, M45. There are 18 objects brighter than magnitude 6.0. This means that theoretically, you should be able to see them with your naked eye in very dark skies. The dimmest of these “bright 18” at 5.8 is M13, the Great Globular Cluster in Hercules. Looking at the list of these brightest objects, I’ve only ever seen four of them with the naked eye: the Pleiades, the Beehive Cluster, Andromeda, and Orion. Maybe if I got to truly dark skies, I could add “trying to see more Messiers naked eye” to the list of things to see. It would be fun to see Hercules with the naked eye. Have any of my readers seen it with your own eyes, or other visual Messiers (not Mark Messier) beyond the big four?
Messier Catalogue Expansion, Anomalies, and Mistakes
As mentioned, Messier’s Catalogue was issued in two installments. When Messier got to 100 objects in 1781, he was ready to issue the second installment. However just as he was submitting the list to be published, Mechain sent Messier a letter with three more objects, getting the count up to M103, which was the number in the final published installment. Messier himself stopped adding onto the list at that point.
His colleague Mechain continued sending Messier additional items, getting the number up to 109. (Mechain observed from a different observatory, outside of Paris.) Finally, the last Messier object, M110, was added when a review of Messier’s notes from his observations of the Andromeda Galaxy (M31) revealed that not only had he seen one of its companions, M32, but both – M110 as well. These objects, M104-110, were added between 1921 and 1967 by various astronomers, first mostly at the urging of astronomer Helen Sawyer Hogg, and later, astronomer Owen Gingerich. They painstakingly reviewed Messier’s notes, correcting mistakes and finding lost objects. The Catalogue is now considered to have 110 items.
In the mistake category, M40 is just a double star. M73 is just an asterism – a group of 4 stars that are at different distances and have no connection to one another. M102 was originally a duplicate observation of galaxy M101. We “know” this because Mechain later wrote a letter disclaiming that M102 was a separate discovery from M101. As a result, for many years M102 was considered to simply be nothing. That is, until the 20th century, when further review of Mechain’s notes revealed that Mechain had made a mistake in his positioning calculations, such that M102 was indeed a separate object that corresponded to NGC 5866. M91 was one of a cluster of eight galaxies in Virgo, but which one? It was misidentified for centuries until it was finally assigned to NGC 4548.
M24 isn’t really an object, per se. It is simply a portion of the star cloud that makes up the Milky Way that was a bit brighter than the surrounding star cloud, due to there being slightly less interstellar dust between it and us to dim it to the same apparent brightness as the rest of the cloud.
Additionally, M47 and M48, two open clusters in Puppis (near Canis Major) were also considered to be lost Messier objects, due to errors in calculating their positions in the sky by Messier. Careful analysis of his notes revealed the source of his errors, and they were later recovered and assigned to NGC 2422 and NGC 2548, respectively.
Messier seemed to be deliberately padding out the initial publication of his Catalogue just to get the number up to 45 items. I mean, come on, M42 and M43? M44, the Beehive Cluster? And M45, the Pleiades? Especially when they’re all visible to the naked eye, this is rather lame. None of these could ever possibly be mistaken for comets. Who’s going to mistake the Pleiades for anything? Really, Messier?
The explanation commonly given for this was that another French astronomer, Nicolas Louis de La Caille, had published the first true catalogue of DSOs in 1755 that contained 42 objects, mostly objects visible from the southern hemisphere, as he was observing near Cape Town in South Africa. Messier obviously felt some competitive urge to top this number with his own Catalogue, so he padded it out to 45.
In addition to the 110 objects that are on the list, there are two other objects labelled “B” that aren’t exactly on the list. This means that Messier or Mechain noted observing them, but the objects were not included in the Catalogue. One of these is M51B, the second galaxy interacting with the spiral of the Whirlpool Galaxy, M51. Mechain observed this as being separate from M51 and reported this to Messier.
The other is M109B. M109 itself (NGC 3992) is a 9.8 magnitude spiral galaxy in Ursa Major. One degree further north is what is called M109B, a mag 10.1 spiral. Mechain discovered this one and reported it to Messier as well.
So, Messier’s goal was to create a catalogue of objects that might be mistaken for comets. He included all types of objects on his list: galaxies, globular clusters, open clusters. But what about all the omissions? There are dozens of open clusters not on the list that would have roughly the same appearance as a comet as the ones he included. How could the Double Cluster not be included? It’s only one of the centerpiece DSOs of the entire sky. As long as we’re up Cassiopeia way, what about the Owl/ET Cluster, NGC 457? Or what about NGC 7789, another nice open cluster in Cass, just a few degrees from M52? And if he was going to include the Pleiades as M45, how could he miss out on the Hyades?
In last week’s blog, I mentioned that a 7.9 magnitude globular cluster, NGC 6723, was nearby and a little bit brighter than another couple of Messier objects, M69 and 70, at magnitude 8.3 and 9.1, respectively. How could he have missed this? As I checked Stellarium when I got back home, I understood why. M69 and 70 are already a couple of the most southerly objects in the Catalogue, both at declination -32 degrees. (The furthest south is M7, the Ptolemy Cluster, at -34 degrees. But it’s also the 5th brightest Messier at magnitude 4.1.) NGC 6723 is even further south, at -36 degrees.
Messier was observing from Paris, at a latitude of 49 degrees. This put a theoretical southern limit on his observations of -41 degrees, but realistically, viewing dim things that close to the horizon is extremely difficult due to atmospheric extinction. NGC 6723 would be only 5 degrees above the horizon at its highest for Messier, deep in the turbulence and murk that exists above the rooftops of Paris. I could see what Messier could not because the DAS dark site is 10 degrees latitude further south than Paris, raising NGC 6723 to almost 15 degrees above the horizon.
The most notable omissions in the Catalogue are all of the great objects of the southern sky. The reason here is simple; they were literally below his observing horizon, so that he could never see them from Paris. None of the best southern sky objects made it in: 47 Tucanae, Omega Centauri, the Eta Carinae Nebula, the Centaurus A Galaxy, the Jewel Box Cluster, the Wishing Well Cluster, to name just a few, and, of course, the Large and Small Magellanic Clouds. How I’d love to go down south and see those!
One of the commonly reiterated facts is that Messier made many of his observations using a 4-inch refractor. But this isn’t quite true. Messier also used a number of reflectors, including two with 7 3/4 inches and 7 1/2 inches of aperture. However, reflectors of this time period were made not with glass mirrors, but a polished metal called speculum, a shiny alloy of copper and tin.
The problem with speculum is that it is less than two-thirds as reflective as the aluminized glass mirrors that we use today, which wouldn’t come into widespread use for another century. Worse, speculum is also prone to tarnishing very quickly, even further reducing the amount of light reflected. The tarnishing led to a need to frequently repolish speculum mirrors. And remember, in a Newtonian, you’ve got two mirrors, even further reducing the amount of light. Two 65% reflectivity mirrors together mean that only 42% of the light that entered the telescope ever even reached the eyepiece. Modern figures in this regard are just north of 90% for commercially available reflectors at modest prices. (We’re talking about Synta and GSO, not Zambuto and Lockwood here.) And because the eyepiece itself wasn’t coated to prevent reflections, even more light was lost before it reached the eye. Because of all this, the effective diameter of the two main 7 3/4 inch and 7 1/2 inch reflectors were 3 1/2 and 2 1/2 inches.
Further, speculum was a heavy metal, meaning that it had problems maintaining the correct parabolic shape as the temperature changed during the night due to thermal expansion and contraction. Because of the weight of the mirror, it retained a lot of heat, meaning that the views were negatively effected by the heat rising into the air off of the surface of the mirror. All of this made using refractors, which do not require such maintenance, and aren’t effected by thermal or cooldown issues, a much easier proposition to use.
Messier’s refractors were between 3.5 and 4 inches in aperture. These weren’t modern 4-inch refractors, with computer-ground lenses and modern anti-reflective coatings on modern glass. No, this was a less than precision ground lens with subpar glass and no coatings. And again, combined with subpar eyepieces as well – which, by the way, were not interchangeable. Each scope had one eyepiece mounted in it, and that was it. In terms of light transmission and clarity, my best guess is that Messier was using a rough equivalent of a modern ST-80 like mine, at best.
More to the point, he wasn’t using a widefield ST-80 capable of scanning a patch of sky over 4 degrees wide at a time; he was using a very long format refractor. If you’ve seen any pictures of telescopes that were in use back in the 18th and 19th centuries, you’ve seen that they’re incredibly long; almost impossibly long. This was to correct for chromatic aberration, which increases with decreasing focal ratios in refractors, and of course, conversely, decreases with higher focal ratios – long skinny refractor tubes.
Early in his career, Messier was using what’s called “ordinary” refractors – with just one objective lens. This was because John Dollond wouldn’t invent the much-improved two-lens achromatic refractor until 1758. Messier’s single lens refractors were 23, 25, and 30 feet long. Yes, you read that right; now think about that for a minute. You can imagine that moving around a telescope of those lengths made his task of finding comets ridiculously hard. Not only that, but those long focal lengths reduced his true field of view, the size of the patch of sky he could see through the scopes, to practically nothing.
Obviously, Messier wasn’t using modern eyepieces with 82, 68, or even 52-degree apparent fields of view. He would have been using Huygenian EPs. Those are the godawful EPs that come with cheapo department store telescopes, the ones we warn beginners against, the ones that are barely fit to be paperweights or doorstops. The ones with about 30 degrees apparent field of view. Combined with the incredible focal lengths of the telescopes he was using, the size of the patch of sky that he could see was about half the width of the full moon, about a quarter of a degree across. That’s positively tiny. On that scale, objects like M13 and M52 would have been so large they would have filled his entire field of view.
Later in his career, he used achromatic refractors. These were about 3 1/2 feet long – just over 1000mm, which is a perfectly reasonable focal length that provided a larger, more usable field of view. He favored using these, for obvious reasons.
Even with all of this, Messier was still able to find and see all of these objects, all the way down to the 10th magnitude. How? Messier’s light pollution situation. In the eighteenth century, there simply wasn’t much. Oh, the streets of Paris were lit up by oil lamps every night, but that’s not so bad – a far cry from the amount of light that our modern mercury vapor or LED streetlights put out. Messier was observing under almost 6th magnitude skies, making his detection of 10th magnitude objects with a four-inch refractor not quite as amazing an accomplishment. The truly amazing part of his feat was finding these objects given the incredibly limited field of view he was working with. Messier’s compatriot, Mechain, was observing separately from outside of the city of Paris, so his skies were inky black.
Because of the much darker sky conditions that Messier and Mechain observed under, it is commonly stated that a 4-inch refractor under today’s modern, brighter sky conditions will show you what Messier was seeing 250 years ago.
However, even though Messier had no light pollution to contend with, he did have to contend with the actual pollution from 800,000 residents of Paris and their chimneys pouring smoke into the sky to keep homes warm during the night. All that soot in the air scattered and absorbed starlight to a certain extent. Pollution made his sky a bit dimmer than it otherwise would have been, and certainly would have dimmed things down at the horizon, where the smoke would have hung.
It is possible to see all 110 Messier objects in one night. This is called a Messier Marathon, which is part of the title of an excellent book by Harvard Pennington, which lays out how you can do exactly that: The Year-Round Messier Marathon Field Guide. It takes all night long because some objects from the season you perform the marathon (which happens to be late winter/early spring) are setting while others from the spring and summer are rising all night long.
You can accomplish what normally takes a couple of years all in one long night – one very long night. You can do a partial marathon of about 80 or even 90 objects on just about any clear night of the year. As I discussed in my previous post, I was all set to do a globular marathon of 25 out of the 29 Messier globulars last week – and it would only have taken about four hours or so. Except that the weather had other ideas. But to get all 110 Messier objects in just one night, the marathon has to be done in March; later in March is better.
It requires careful planning – meaning the ordering of when you view the objects. You have to know which ones are setting immediately upon starting the marathon and have to be found during twilight (M74, 77 and 33), and which ones are rising that you have to catch even as dawn is breaking (M30). Of course, Pennington’s book guides you in this.
Critical in this regard is observing from a location with a low horizon – meaning no mountains, away from tall trees. If the terrain or light pollution rises just 8 degrees above the horizon, that means that you’re missing out on a half hour of observing. If either rises 15 degrees, that’s a full hour you’ve lost. And you’ll need that half hour or hour to catch those setting or rising objects in the most difficult conditions.
You need to avoid an observing site where the east or west is obstructed in this manner – so being on the mountain is better than being near it. Also, a more southerly observation site is better because the objects in Scorpio and Sagittarius rise higher in the sky.
And, of course, the observation spot should have almost no light pollution, either. Nott just from ambient sources, but also those in the sky: the marathon has to be done as close to the night of the new moon as possible so as to avoid or at least minimize the effects of light pollution from moonlight.
Messier’s later life
In 1770, at the age of 40, Messier married. However, in 1771, his wife and infant son died within a few days of childbirth,. It is said that he regretted not being able to find a comet (due to his wife’s illness at the time) more than the death of his wife, but this story seems apocryphal.
Shortly after adding the 100th object to his list, and then adding three more observations from Mechain to get the number up 103, he published his second installment of the list in 1781. Meanwhile that same year, a German/English astronomer, William Herschel, had discovered Uranus. Ahem. Insert joke here. Insert it waaay up there.
Messier corresponded with Herschel and immediately took up observation of the object, whose true nature was as yet unknown. Was it a comet? Or something else? Based partially on Messier’s observations of its motion through the sky, other astronomers who were more talented in mathematical calculations than Messier were able to calculate the orbit of Uranus and conclude that the “Georgian Star”, as Herschel wanted to call it (to score brownie points with England’s King George), was actually a planet.
After that, he planned to make updates to his list as he discovered further nebulosities, but later in 1781, he took a nasty 25-foot fall into an ice cellar, breaking his arm, wrist, thigh, hip, and two ribs. He was out of commission recuperating for a year. When he returned to observing, he concentrated solely on finding comets, and did not add further to his Catalogue.
The French Revolution was not kind to Messier. He lost his salary and his pension, but fortunately, not his life. Regardless, he continued to observe, and discovered another comet even during the Reign of Terror in 1793. However, with the coming of Napoleon, Messier’s life improved again. In 1806, Napoleon personally awarded Messier with the cross of the Legion of Honor.
In return, in 1808, Messier paid for the publication of a pamphlet announcing that the Great Comet of 1769, which Messier had observed, was a portent of good favor – specifically, Napoleon’s birth, the week after the observation. Messier lost a lot of credibility with the astronomical community because of this, as by this time, the idea that comets influenced events on earth had been discarded as being pseudoscientific astrology, not astronomy. Messier himself was well aware of this, stating in a footnote in his pamphlet, “Without doubt, there is nobody who still thinks that the stars have any influence on events on earth; but this great comet, which is different from all others, appeared at the birth of NAPOLEON THE GREAT, at a remarkable time to attract the attention of the whole world, and especially of the French people.” (Emphasis in original.)
During this same time period, Messier observed the “new planets” Ceres and Pallas, and codiscovered his final comet in 1801, at the age of 71. In his later years, he continued observing, but was unable to contribute further due to decreasing eyesight. He suffered a stroke in 1815, and passed away in 1817, at the age of 86. Mechain had escaped the French Revolution to Spain, but lost his estate. He died of yellow fever there on a different expedition under Napoleon in 1804.
If you’re interested in further information about Messier, there’s a good biography online here, from which much of the biographical information presented here was taken and condensed.