Astronomers are always talking about ‘M’ number this and ‘M’ number that so what are these ‘M’ numbers ?
The ‘M’ is short for Messier and refers to in an object from the Messier Catalogue of ‘fuzzy’ objects. Charles Messier was a French comet hunter who spent his life searching for and studying comets. While scanning the night sky Messier kept finding ‘fuzzy’ objects which were not stars, looked like comets but did not appear to move like comets. To avoid confusion Messier made a list of these ‘fuzzy’ objects so he could avoid them when he was searching for new comets.
Telescopes in Messier’s time were not as good as telescopes of today and even the telescope used by many amateurs today are far better than the best telescopes available in the late 1700’s. We now know these objects are nebulae, galaxies, star clusters, ring nebulae and super nova remnants. To Messier these objects were a nuisance, to the modern amateur astronomer they are the things to look for.
There are now many other catalogues of deep sky objects with millions of objects listed but the 110 Messier objects are still the things most amateur astronomers start observing.
Galaxies are huge clusters of stars like our milky way galaxy. Some or the galaxies listed by Messier are M31 in Andromeda and M65, M66, M95 and M96 in Leo.
Open Star Clusters are groups of between tens to thousands of stars which have formed from a collapsing cloud of gas and dust. M45 the Pleiades (Seven Sisters) in Taurus is one of the most beautiful of the open clusters.
Globular Clusters are groups of between thousands and a million stars which form a halo above and below the main disc of our galaxy. M13 in Hercules is a good example.
A Ring Nebula is the remains on a star of about the same size as our star The Sun. After about ten billion years the Hydrogen which has powered the star will run out. The star becomes inflated like a giant balloon. Eventually the outer parts of the star drift off into space and form a huge bubble. As we look through the bubble we see more material through the edge so it appears more like a ring. The Ring nebula in Lyra M57 is the most famous.
One particular type of Super Nova produces a fuzzy patch.. This is where a giant star between 5 to 30 times the mass of our Sun reaches the end of its existence. The star becomes very unstable until it eventually explodes and completely destroys the itself. The super nova remnant known as the Crab Nebula, in Taurus, is the first in Messier’s list and is therefore designated as M1.