Messier Questions & Answers

This is not exactly what is an FAQ, although we try to answer all the most common questions related to Charles Messier and his catalog.


How do I correctly pronounce the name "Messier" ?

For what I know, the French say messy-AYYH for this name.

What telescopes do I need to observe the Messier objects? What telescopes had Messier used?

The question "what telescope is needed" must acurately be answered separately for every individual object: Some are visible to the naked eye, and few even under considerable bad conditions, but many others require some instrumentation. A 3-inch refractor (or equivalent) will manage the lot of them, but for the faintest objects of Messier's catalog, the present author would recommend a 4-inch refractor or equivalent; this will be sufficient to view them all, provided that the instrument is equipped so that both rich field/low magnification and (considerably) high magnification/small field observations are possible; otherwise you will perhaps miss some of the big, low surface brightness objects, especially M33, the Triangulum galaxy.

Most of today's amateur instruments, starting from 3.5 to 4 inch free aperture (unobstructed; about 4.5 to 5 inch Newtons), are superior to Messier's telescopes, but he had the advantage of a very dark and clear sky all the time when it was not cloudy over Paris. So the success of finding his objects may more depend on the choice of a good (dark) place than on superiority of instrumentation.

I've heared about "dubious" and "missing" as well as "additional" Messier objects. What about that?

All these really exists.
Dubious Messier objects:
Although Messier called his list a "Catalog of Nebulae and Star Clusters" (where we know today that some nebulae are actually galaxies), there are three objects that are neither:
  1. M24 is a Milky Way star cloud which contains an 11th mag open cluster (NGC 6603). The NGC erroneously takes this cluster for M24, although Messier without doubt described the star cloud.
  2. M40 is a double star which Messier found and measured when looking in vain for a non-existent nebula reported by 17th century observer Jan Hevelius (this answers the question why this object is included: Messier had logged the position, thus it got a number).
  3. M73 is a group or an asterism of four 10th to 12th magnitude stars, which Messier measured at the same time when he determined M72's position.
Some versions of the list omit some or all of these dubious objects, though they are without doubt real objects, and their appearance was correctly described by Messier. However, these ``dubious'' objects can be hardly classified as deep sky objects at all: M40 and M73 are multiple stars (or asterisms), while M24 is perhaps no object at all, but a "window in the dust" obscurring the Milky Way, and/or a larger portion of a spiral arm (see the M24 page).
Missing Messier objects:
Of the 103 objects in the full printed version of Messier's catalog, only 99 show up as described at their position, while four objects are missing: M47, M48, M91, and M102. For at least three of these entries, the described objects exist, but Messier gave a wrong position, only the case of M102 is still controversially discussed. Look at the Discussion of the missing Messier objects.
Additional Messier objects:
From the studies of Messier's personal notes, publications, the text of the catalog, as well as the notes and correspondence of his friend Pierre Méchain, experts have added 7 more objects, numbers M104 to M110, to his catalog; these are the additional Messier objects.

Why are there bright Deep Sky objects which are not in Messier's catalog?

Messier's catalog was not intended as a Deep Sky catalog at all, but as a list of nebulae which can easily fool comet hunters by looking like comets. Thus it contains mainly objects which, at least in the rather small instruments Messier has used, or to the unaided eye, look like comets. Moreover, Messier did a more or less unsystematic search for comets, and thus it depended on chance to a good part if he found a particular object.

Why are all Messier objects north of declination -35?

This one is easy: Because Messier did all his observations from Paris, which is at 49 degrees northern latitude.

Why is the Double Cluster not in Messier's catalog?

Because usually, Messier did not include objects which resemble a comet so bad as the famous cluster. This leads to the question why he included the Orion Nebula, the Pleiades, and Praesepe. Those were included in one night, that of March 4, 1769, the only night when Messier made an exception. This night, however, falls into a season when the Double Cluster is worst observable, i.e. over horizon all the day. Otherwise, the two clusters would probably have been assigned Messier numbers 46 and 47 !

One may of course ask: Why did he make this exception at all ? Or: Why did he never again include such brighter objects ? As we cannot ask Charles Messier himself, we can no more find out if there is a deeper reason, but probably it is not.

Why is the Cat Eye nebula NGC 6543 missing?

The prime reason may be chance, another reason may be that comets occur more frequently in low ecliptic latitudes, a fact Messier was probably aware. So he was not looking exactly near the ecliptical pole, where the Cat Eye Nebula (NGC 6543) is situated.

Why are then some objects included which are not anyway similar to comets?

First, because this catalog was more Messier's logbook for measured object positions.

Why is M40 quite an inconspicuous Double Star?

Messier scanned the region of this object when he was looking for a non-existing nebula reported by the 17th century astronomer Johann Hevelius (who had reported few real and several nonexistent nebulae). He ended up in the assumption that his object M40 (today also known as Winnecke 4) was the binary which Hevelius had erroneously seen as nebulous. It seems however that Hevelius had observed another (nearby) double star, 74 Ursae Maioris.

Why did Messier include the Orion Nebula, the Pleiades, and Praesepe?

It is somewhat unusual that the Orion Nebula M42 together with M43 and the bright star clusters Praesepe M44 and the Pleiades M45 have found their way into Messiers list; Charles Messier usually only included fainter objects which could be easily taken for comets (this is one reason why the Double Cluster Chi and h Persei is not in Messier's catalog). But in this one night of March 4, 1769, he determined the positions of these wellknown objects (to say it with Owen Gingerich) `evidently adding these as "frosting" to bring the list to 45', for its first publication in the Memoires de l'Academie (see also the remark at M42).

Interested readers may ask themselves why it was important for him to have his list at 45 rather than 41 objects. One can only speculate on this subject, but perhaps one answer may be that Lacaille's catalog of 1755 happened to contain 42 entries, and he wanted to beat this number.

One may now ask: Why did he think, in another night, the Andromeda galaxy M31 should be in his list ? You can guess the answer: This object may be easily taken for a fainter (4th mag) comet, even with the naked eye (this may be one of the reasons that it was not cataloged in ancient times, because it was thought to be transient like comets, and as them, regarded as an atmospheric, not astronomical phenomenon).

Why did a small group of 4 stars get the number M73?

This is another case of a position measurement, which in this case was determined simultaneously with that of globular cluster M72. The small group of four stars got the number M73.

Why did Messier, in 1782, cease to extend his catalog?

First, after the catalog was submitted for publication, he added one more object more or less immediately, the Sombrero galaxy M104 (May 1781). Parallel to and after that, he was apparently busy in observing and calculating the orbit of Herschel's newly discovered planet, Uranus. Later that year, he had his awful accident by falling into an ice cellar, which stoke him to bed for more than a year. When he resumed observing in 1782, he observed a transit of Mercury, and took up comet hunting virtually immediately. But never again he extended his catalog of nebulous objects. It is not improbable that one decisive reason was that now Herschel had begun his systematical search for nebulae with much more powerful equipment and soon discovered thousands of objects, so that Messier with his small instuments realized that he could no more compete, and lost interest.

Many years later, in 1801, he claimed that he had plans to rearrange his list, and add more recently observed objects, but this plan never became reality.

What is a Messier Marathon ?

The Messier Marathon is a term describing the attempt to find as many Messier objects as possible in one night. The opportunity to find all objects is given for (and limited to) observers in rather low northern latitudes in late March of each year, when the Moon is near its new phase; otherwise you are restricted to find as much as possible, but cannot find all of them in one night. As this is quite a challenging endeavor for skilled amateur observers, these pages provide a Messier Marathon section.

Are there Messier objects which are not in the NGC ?

Yes, four:
  1. M25; this is IC 4725
  2. M40, the double star Winnecke 4
  3. M45, the Pleiades; however, this cluster is associated with nebulae which have NGC numbers
  4. M24, the Milky Way Patch in Sagittarius; it contains however the 11th magnitude cluster NGC 6603 which is sometimes erroneously listed as M24. Also, it may be that IC 4715 is M24.

Are there more materials available on Messier and his catalog?

Yes, quite a number of. Look at the List of Messier Goodies which is part of this database.

How can I get hardcopies of these images ?

This is one of the most frequently asked questions .. well, SEDS and me don't provide any hardcopies of our materials. However, you may get images of many of the Messier objects in the form of slides, prints, posters, and more, from many suppliers of astronomical goodies, and e.g. several book dealers. You may find some information in my " List of Observatories Making Astrophotos Publicly Available"; many of the sources listed there have Messier object materials. Also, please check the other information sources section in this file.

May I use these materials ?

These materials are all free for personal use. For any other kind of usage, please determine if there are any third-party rights and royalties which should be observed (I try to indicate this near the images, but cannot promise that the lack of such info implies there are none); please check our usage regulations for more detail, and feel free to contact me in case of further questions.

SEDS and me do not restrict any appropriate usage of these materials, but in many cases, there are third-party royalties which are to be observed, especially in case of any for-profit usage.

What if I don't find my question on Messier and his catalog answered here?

Best you can do is contact the author of the questions (Hartmut Frommert) and ask your question. There's a good chance that it is interesting enough for being added to this list.

I have potential contributions to, or found an error in the Messier pages. What can I do?

The maintainer of the pages appreciates any form of constructive feedback, from simple comments ("this is fine" or "that may be better another way", or equally: "that's bad") to any form of contributions, and reports of any errors. Too few readers take the time for this most important sort of response ! It is most important for the integrity and wellness of this database that all bugs and errors are fixed, regardless if it is erroneous statements, invalid links, or any other sort of errors. Also, it may be that you have a grand idea for enriching this service, or you think something may be done better. In all these cases, please take the few minutes to submit a message.

Where do I find information on similar but other threads?

Some information on related fields may be found in the FAQ (Frequently Asked Questions) lists of various newsgroups, mailing lists, etc. For the reader of this page, the following may be of interest: Some introductory information for interested people is included in these pages.

Hartmut Frommert
Christine Kronberg

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Last Modification: March 7, 2012