Astronomy

The star that the planets revolve around and which gives out the heat and light energy necessary to enable living organisms to survive on Earth.

From Collins Dictionary of Astronomy
The innermost and, with a diameter of 4878 km, the second smallest planet in the Solar System, orbiting the Sun in 87.97 days at an average distance of 0.39 AU. It has no natural satellite.

The second planet from the Sun, clearly visible from the Earth as a bright morning and evening star, its orbit lying between those of Mercury and Earth.

The third planet from the Sun.

Natural satellite of a planet (see satellite, natural) or dwarf planet, in particular, the single natural satellite of the earth.

Fourth planet from the Sun. It is much smaller than Venus or Earth, with a mass 0.11 that of Earth.

The fifth planet from the Sun, and the largest in the solar system, whose orbit lies between those of Mars and Saturn.

Sixth planet from the Sun, and the second-largest in the Solar System, encircled by bright and easily visible equatorial rings. Viewed through a telescope it is ochre.

Seventh planet from the Sun, discovered by German-born British astronomer William Herschel in 1781.

The eighth planet from the Sun, the outermost of the four ‘gas giant’ planets; discovered in 1846 as a result of a prediction by Leverrier to explain anomalies in the observed orbit of Uranus.

Dwarf planet. Until its reclassification in 2006 it was considered to be the smallest and, usually, outermost planet of the Solar System.

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.

The galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon.

From The Columbia Encyclopedia
Orion Nebula, bright diffuse nebula in the constellation Orion; also known as the Great Nebula of Orion and cataloged as M42 or NGC 1976.

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 The Hutchinson Unabridged Encyclopedia
Brightest star in the night sky, 8.6 light years from the Sun in the constellation Canis Major.

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.

Illumination of the night sky, known popularly as the northern and southern lights.

In the solar system: a small body consisting of a coma, a nucleus and a tail, which is composed mainly of frozen gas, dust and rock and follows an elliptical orbit around the Sun.

One of the 88 areas into which the sky is divided for the purposes of identifying and naming celestial objects.

In astronomy, partial or total obscuring of one celestial body by the shadow of another.

Grouping of millions or billions of stars, held together by gravity.

Increase in the number of meteors observed in a particular part of the sky.

Appearance of a small particle flying through space that interacts with the earth's upper atmosphere.

From The Handy Astronomy Answer Book
Generally, types of nebulae are described either by their appearance (for example, dark nebulae, reflection nebulae, and planetary nebulae) or the physical processes that create them (such as protostellar nebulae, protoplanetary nebulae, or supernova remnants).

Celestial source that appears to flash at radio and other wavelengths at regular intervals, ranging from a few seconds to a few thousandths of a second. Pulsars are rapidly rotating neutron stars.

Group of related stars, usually held together by gravity. Members of a star cluster are thought to form together from one large cloud of gas in space.