a comparatively young, irregularly shaped group of stars, often numbering up to several hundred, and held together by mutual gravitation; usually found along the central plane of the Milky Way and other galaxies.
a loose grouping of stars
See open cluster.
A loose, irregular grouping of stars that originated from a single nebula in the arms of a spiral galaxy. Compared to globular clusters, open clusters generally contain younger and fewer (from a hundred to several thousand) stars and are confined to the disk of the galaxy. Because they are young, open clusters are sometimes still surrounded by the leftover gas and dust from which they formed. Visible from Earth with just a pair of binoculars and containing over 3,000 stars, the Pleiades is the best known open cluster. Also called galactic cluster. Compare globular cluster.
- Galactic coordinate system
galactic coordinate system The coordinate system in which a celestial object’s position on the celestial sphere is described in relation to the structure of the Milky Way galaxy. ◇ An object’s galactic longitude is measured along the galactic equator, a great circle on the celestial sphere that follows the band of the Milky Way. The […]
noun, Astronomy. 1. the great circle on the celestial sphere that is equidistant from the galactic poles, being inclined approximately 62° to the celestial equator and lying about one degree north of the center line of the Milky Way. noun 1. the great circle on the celestial sphere containing the galactic plane
- Galactic halo
noun 1. (astronomy) a spheroidal aggregation of globular clusters, individual stars, dust, and gas that surrounds the Galaxy galactic halo A large, spherical region of relatively dust-free space surrounding a spiral galaxy such as the Milky Way. The inner regions of the galactic halo contain globular clusters of very old stars, while the outer regions […]
noun, Astronomy. 1. the angular distance from the galactic equator of a point on the celestial sphere.