The list of 110 deep-sky objects, M1 to M110, that the comet hunter Charles Messier published from 1774 so as not to mistake them for comets (the last entries were added later). It gathers the finest clusters, nebulae and galaxies visible from mid-northern latitudes. It is the ideal observing programme for beginners.
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Related terms
- NGC and IC
The New General Catalogue, published by John Dreyer in 1888, lists 7,840 deep-sky objects; its two supplements, the Index Catalogues (IC), add 5,386 more. One object can have several names: M31 is also NGC 224. The brightest NGC objects are within reach of a 150 mm telescope.
- Open cluster
A group of a few dozen to a few thousand young stars, born together from the same gas cloud. The Pleiades (M45), about 440 light-years away, are the best-known example. Many look superb in binoculars or at low power.
- Galaxy
A vast system of billions of stars, gas and dust held together by gravity. The Andromeda Galaxy (M31), 2.5 million light-years away, is visible to the naked eye as an elongated smudge. In a telescope most look like faint grey glows: their light set off millions of years ago.
- Nebula
A cloud of gas and dust in space. Depending on how it shines, or does not, it is called an emission, reflection, dark or planetary nebula. The word once also covered galaxies, whose nature was unknown.
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