A star with very low mass (less than 8% of that of the Sun) such that thermonuclear reactions cannot occur, its dim appearance being the result of contraction due to gravitational force and constant release of energy.
From Astronomy Encyclopedia (M31, NGC 224) One of the two giant spiral galaxies in the local group of galaxies, the other being our Galaxy, the Milky Way. M31 is the nearest spiral to the Milky Way, some 2.4 million l.y. away
Pair of stars moving in orbit around their common centre of mass. Observations show that most stars are binary, or even multiple - for example, the nearest star system to the Sun, Rigil Kent (Alpha Centauri).
From The Columbia Encyclopedia Diffuse gaseous nebula in the constellation Taurus; cataloged as NGC 1952 and M1, the first object recorded in Charles Messier's catalog of nonstellar objects. It is the remnant of a supernova that was observed in 1054 by Chinese and Arab astronomers to be as bright as Venus.
From Collins Dictionary of Astronomy A spherically symmetrical compact cluster of stars, containing from several tens of thousands to maybe a million stars that are thought to share a common origin. An example is the Great Cluster in Hercules. A few globular clusters, such as Omega Centauri, appear to be slightly flattened.
From The Hutchinson Unabridged Encyclopedia In astronomy, an open star cluster about 400 light years away from Earth in the constellation Taurus, represented as the Seven Sisters of Greek mythology. Its brightest stars (highly luminous, blue-white giants only a few million years old) are visible to the naked eye, but there are many fainter ones.
From The Columbia Encyclopedia Brightest star in the constellation Centaurus and 3d-brightest star in the sky; also known as Rigil Kent or Rigil Kentaurus; 1992 position R.A. 14h39.1m, Dec. -60°49'. It is a yellow main-sequence star of the same spectral class (G2 V) as the sun and of about the same size and mass.
From The Hutchinson Unabridged Encyclopedia
Brightest star in the constellation Boötes and the fourth-brightest star in the night sky. Arcturus is a red giant about 28 times larger than the Sun and 70 times more luminous, 36 light years away from the Sun.
From Astronomy Encyclopedia
The star α Orionis, marking the right shoulder of Orion, distance 427 l.y. It is a red supergiant of spectral type M2 Ib, about 500 times the Sun's diameter and 10,000 times as luminous.
From The Hutchinson Unabridged Encyclopedia Second-magnitude star in Ursa Major, where it marks the middle of the handle of the Plough. Mizar and Alcor, a fourth-magnitude star, form a visual double star.
From The Columbia Encyclopedia Bright star in the constellation Orion; Bayer designation Beta Orionis; 1992 position R.A. 5h14.2m, Dec. -8°13'. A huge, blue supergiant of spectral class B8 Ia, Rigel has an intrinsic brightness about 40,000 times as luminous as that of the sun.
From Collins Dictionary of Astronomy A conspicuous white star, apparently blue in color, that is the brightest star in the constellation Lyra. It was the pole star about 12,000 years ago, at the end of the last Ice Age. Because of precession, it will be the pole star again around ad 14,000.
From Atlas of the Universe Mercury, the innermost planet, is never easy to study from Earth. It is small, with a diameter of only 4878 kilometers (3030 miles); it always stays in the same region of the sky as the Sun, and it never comes much within 80 million kilometers (50 million miles) of us.