Universe Today
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects in the night sky. In time, he would come to compile a list of approximately 100 of these objects, with the purpose of making sure that astronomers did not mistake them for comets. However, this list - known as the
Messier Catalog
- would go on to serve a more important function.
In addition to cataloging some of the most beautiful objects in the night sky, this list would come to be an important milestone in the discovery of Deep Sky Objects. The second object to make the list is known as Messier Object 2 (aka. M2 or NGC 7089), one of the largest globular cluster in the Milky Way, and which is located in the constellation
Aquarius
.
Description:
As one of the largest known globular clusters, Messier 2 is a rich, round concentration of gravitationally bound stars that orbits the galactic core. Located about 33,000 light years (10,000 parsecs) from our Solar System, this cluster measures some 175 light-years in diameter and is believed to contain about 150,000 stellar members - including 21 known variable stars. Its brightest stars are red and yellow giant stars.
Because its members are so tightly packed together, it has a density classification of II - which is reserved for clusters that are particularly rich and compact. And like most globular clusters, M2's central region is highly compressed, measuring just 3.7 light years in diameter. It's tidal influence, on the other hand, has a radius of 233 light years, beyond which members stars would escape due to the influence of the Milky Way's tidal forces.
Positioned well beyond the galactic center, M2 is also noted for its elliptical shape, and is believed to be as much as 13 billion years old.
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The constellation Aquarius. M2 is visible right of center, above Beta Aquirii. Credit: iau.org
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History of Observation:
M2 was first discovered by Jean-Dominique Maraldi in 1746 while observing a comet with Jacques Cassini. According to Cassini's notes, which detail the discovery, the two believed it to be a "nebulous star" at the time:
The object was independently recovered by Charles Messier in 1769, though he too mistook it for something else. In his notes, which were also taken on September 11th (fourteen years later), he described the object as a nebula:
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Charles Messier, French astronomer, at the age of 40, by Nicolas Ansiaume. Credit: Public Domain.
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Ultimately, it was William Herschel who finally resolved Messier 2 into the object we recognize today. This took in 1783, where - according to his notes - he was able to resolve individual stars:
Locating Messier 2:
Messier 2 is located approximately 5 degrees (about 3 finger widths) north of Beta Aquarii, on the same declination as Alpha Aquarii. M2 is sufficiently bright enough to be seen in urban settings where light pollution is a factor, and can alternately be found by looking about 10 degrees (a fist width) south/southwest of Epsilon Pegasi (Enif).
Using binoculars, it will appear as a large, fuzzy ball with little or no resolution. To amateur astronomers using small telescopes, individual stars will be visible around the outer edges, with resolution improving significantly with aperture size of 6'' or more. Those with large telescopes, and who are looking for a challenge, should look for a dark dust lane which crosses the north-east edge of this globular cluster.
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An all-sky map showing the distribution of Messier objects. Credit: Jim Cornmell/Wikimedia Commons
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Of course, John Herschel saw it as "It is like a heap of fine sand!" which is perhaps as apt an description as can be rendered. Through a large telescope, the globular cluster does resemble a glittering mass of sparkling granules.
And for your convenience, here are the vital statistics of this globular cluster:
- Object Name
-
Messier 2
- Alternative Designations
-
NGC 7089, GC 4678, Bode 70
- Object Type
-
Class II Globular Cluster
- Constellation
-
Aquarius
- Right Ascension
-
21 : 33.5 (h:m)
- Declination
-
-00 : 49 (deg:m)
- Distance
-
33 (kly)
- Visual Brightness
-
6.5 (mag)
- Apparent Dimension
-
16.0 (arc min)
Good luck searching for this and other Deep Sky Objects!
We have written many interesting articles on Messier Objects here at Universe Today. For instance, here's Tammy Plotner's
Introduction to the Messier Objects
,
M1 - The Crab Nebula
, and David Dickison's articles on the
2013
and
2014
Messier Marathons.
Be to sure to check out our complete
Messier Catalog
.
For more information, check out the
SEDS Messier Database
.