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.
Contents
For what I know, the French say messy-AYYH for this name.
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.
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:
- 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.
- 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).
- 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.
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.
This one is easy: Because Messier did all his observations from Paris, which
is at 49 degrees northern latitude.
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.
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.
First, because this catalog was more Messier's logbook for measured object
positions.
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.
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).
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.
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.
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.
Yes, four:
- M25; this is IC 4725
- M40, the double star Winnecke 4
- M45, the Pleiades; however, this cluster is
associated with nebulae which have NGC numbers
- 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.
Yes, quite a number of. Look at the
List of Messier Goodies
which is part of this database.
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.
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.
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.
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.
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
[contact]
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Last Modification: March 7, 2012