Deep-sky objects (DSOs) or Deep Sky[citation needed], which differs from deep space, is a term used by amateur astronomers to describe mostly faint astronomical objects outside the solar system, such as star clusters, nebulae or galaxies. These objects are hundreds to billions of light-years distant from Earth.
Nearly all clusters and nebulae are contained within galaxies, and there are a number of galaxies visible to the naked eye. They are, in order of closeness, the Milky Way, the Large Magellanic Cloud (approximately 160,000 light-years away[citation needed]), the Small Magellanic Cloud (about 200,000 light-years away)[citation needed], and the Andromeda Galaxy, (about 2.5 million light-years away).
Types of deep sky objects:
These are classified by several catalogues: the Messier catalogue of 110 objects, the much more comprehensive New General Catalogue (which contains nearly 8,000 objects[1]), and several others. Many sets of these and other objects from more specialised catalogues such as the Uppsala General Catalogue are used by amateurs as a test of their observing skills and their equipment. Messier marathons occur at a specific time each year and involve observers trying to spot all 110 Messier objects in one night. A much more demanding test known as the Herschel 400 is designed to tax larger telescopes and experienced astronomers.
References
See also
- Concise Catalog of Deep-sky Objects: Astrophysical Information for 500 Galaxies, Clusters and Nebulae, by W. H. Finlay, ISBN 1-85233-691-9. Springer, London.
- How to observe deep sky objects
- Clickable table of Messier objects
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