The Messier Catalogue
On most modern day star charts for amateur
astronomers you will see some objects marked with "M" numbers. The
M stands for the Messier Catalogue, a catalogue of 109 bright deep sky
objects found above a declination fo 350 south. But who
was Messier and why do we still use his catalogue numbers?
Some Messier objects imaged by the Hubble Space Telescope
Left: Inside the Eagle Nebula, M16. Photo credit: J. Hester & P.
Scowen (AZ State Univ.), NASA
Centre: The Ring Nebula, M57. Photo Credit: Hubble Heritage Team
Right: M80, a globular cluster in Scorpius Photo Credit: Hubble
Heritage Team (AURA/STScI/NASA)
Charles Messier was a Frenchman who lived
from 1730 to 1817. He moved to Paris to begin his astronomy career
at the age of 21. Although he observed and recorded many other astronomical
phenomena he became most famous for his comet discoveries. From the
discovery of his first comet in 1764 nearly all new comets found
in the next fifteen years were found by him. Over his lifetime he
found 21 comets and earned himself the appelation of the "Ferret of Comets"
by the King of France at the time.
It was because of his devotion to comet-hunting
that his catalogue came about. After observing the Crab Nebula in
Taurus as he was following a comet through the area he wrote:
"What caused me
to undertake the catalogue was the nebula I discovered above the southern
horn of Taurus on September 12, 1758, while observing the comet of that
year....This nebula had such a resemblance to a comet, in it's form and
brightness, that I endevoured to find others, so that astronomers would
not confuse these same nebulae with comets just beginning to shine."
In his day, the telescope was still a small
instrument compared to today's giants and "new" objects were being seen
and catalogued all the time. Anything that could not be resolved
into stars was called a nebula (meaning 'mist'). He collected
some objects that were already known but also discovered many more new
ones. The first part of the Catalogue, up to M45, was published in
1774. A second part including up to 100 was finished in 1781, but
not published until 1784. He was helped in the latter half by Pierre
Méchain, who alerted him to the cluster of galaxies in the Virgo
- Coma Berenices region. Méchain made more observations that
were not published at the time. Several unfortunate incidents
occured that stopped any further discoveries - Messier fell down into an
ice cellar and broke several bones that took a year to recover from and
then politcal unrest developed into the French Revolution.
Research into Messier's notes saw several
more objects added to the list in the 20th century. M104 - M107 were
added in 1921, shortly after M108 and M109 were included. M110, the
last object, was only proposed as an addition during the 1950's and there
is still some debate as to whether or not it should be included.
Several objects were also considered "missing" in that there are no visible
objects in the positions recorded by Messier. M102 was a duplicate
of M101 and although Méchain wrote to the publishers of the day
alerting them to this fact, the letter was not noted again until 1947.
Over time the Messier catalogue was incorporated
into the New General Catalogue (NGC) along with several other catalogues.
Interest was rivived again during the 1950's and 1960's and soon after
Messier Marathons were born. To complete the marathon you must
observe all 109 objects in a single night. In the northern hemisphere
this can be done during the New Moon closest to the March Equinox.
Here in Australia we can't see all the objects so can't complete one in
the intended way. But regardless of the time of year there are always
many Messier objects in view at any time.
M42/43, the Great Orion Nebula.
The Messier Catalogue contains examples
of all types of objects: 39 galaxies, 29 globular clusters, 27 open clusters,
6 diffuse nebulae, 1 supernova remnant, 1 double star, 1 asterism, 1 bright
patch of the Milky Way and one duplication. The Great Orion Nebula
is one of the most well known of the Messier Catalogue as it is so easy
to find in telescopes, binoculars and even the naked eye. Other frequently
viewed Messier objects are the open clusters M6 and M7 near the sting of
Scorpius, the Pleiades are M45, M31 the Andromeda galaxy and M8 the Lagoon
Nebula in Sagittarius.
Working through the Messier Catalogue in
your own telescope is a great introduction to deep sky viewing. By
the time you finish a large proportion of it you should become familiar
with both your telescope and your star charts and be ready to start searching
for more elusive objects. A fair proportion of the objects can be
seen in binouculars as well.
For a look at the catalogue, you can go
to the SEDS Messier database at www.seds.org/messier/
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