June 26, 1730 - April 12, 1817
Charles Messier (1730-1817) was a French astronomer who developed an intense interest in comet hunting. While he had other achievements to his credit, this was his chief occupation during his long observing career. In this, he was so successful that he probably observed half of the comets known in his time. He discovered about twenty.
It was to keep track of the star clusters and nebulae which might have otherwise confused him by their comet-like appearance, that he began to catalogue and describe them.
In commenting on his catalogue in later years, he frankly stated that he had compiled it in order to aid other comet hunters. There is a slight touch of irony in the fact that Messier's chief claim to immortality grew out of his efforts to rid himself of a nuisance to what, he felt, was his important life's work. As might be expected, Messier's telescopes were all modest instruments, none of them exceeding the capacity of telescopes amateurs can expect to own today.
Open Clusters are groups of young stars, often hot and bluish, and their individual stars can easily be seen with a small telescope or sometimes with the naked eye.
Globular Clusters contain larger number of stars and are much more compact. They are found outside the galaxy plane and the stars are older.
Diffuse Nebulae are areas of the raw materials, dus and gas, from which stars are born. These Diffuse Nebulae are found along the spiral arms of the Milky Way, and are visible in other nearby galaxies as well. In an Emission Nebula one or more hot stars causes the nebula to emit light of its own. They have a reddish glow. A Reflection Nebula only reflects light from nearby stars and shows a blue colour.
Planetary Nebulae have nothing to do with planets, but their name arose from their disk-like appearance. They are almost spherical cast-off shells of gas from very hot stars, late in their life spans. Often the ionized gas has a greenish colour.
Galaxies are the most remote objects: huge systems of stars, clusters and nebulae, like our own Milky Way. There are several types of galaxy: Elliptical, Spiral, Barred Spiral and Irregular.
Source of the above text: The Cambridge Star Atlas by Wil Tirion; ISBN 0 521 80084 6
Extensive information about the Messier Catalogue has been made available by the SEDS organization.
Click here to view my images of the Messier catalogue.