ASTRONOMICAL TERMS

The proper names of astronomical bodies are capitalized; generic terms are usually lowercased:

the Virgo cluster; Local Group; our local supercluster

the Milky Way, the Milky Way galaxy; galaxy NGC 7252; Andromeda galaxy, or M31

supernova 1981b, or SN 1981b; supernovae, quasar 3C 273

constellation Orion; Cassiopeia (Lady in the Chair); the Southern Cross; Ursa Major (Great Bear)

the Horsehead Nebula; the Great Spiral Nebula of Andromeda, the nebula

Van Allen belt, Kuiper belt

Large and Small Magellanic Clouds, but Oort cloud

Polaris, the North Star; Barnard's star; Eta Carinae; Mu Arae; Gliese 236; 55 Cancri

Halley's comet or comet Halley

the asteroid Geographos, Allende meteorite

Great Red Spot, Planet X

aurora borealis, aurora australis

big bang, black hole, the solar system

Objects are sometimes designated by a catalog number or abbreviation and a number:

Abell 2218, or A 2218 New General Catalogue 6165, or NGC 6165

Messier 31, or M31 Lings 1251 or L1251.

The names sun and moon are lowercase. Earth is capitalized as the name of our planet whether used in context with other planet names or not. Do not capitalize planet in: planet Earth. Do not capitalize when meaning dirt or the terrestrial part of our planet compared with sea and sky and in compounds such as earthquake, earth-shattering, earthbound.