Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.
There are 2759 entries in this glossary.| Term | Definition |
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| Little Bear |
English name for the constellation Ursa Minor.
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| Little Dipper |
A popular North American name for the constellation Ursa Minor, describing the figure formed by its main stars: Beta β, Gamma γ, Eta η, Zeta ζ, Epsilon ε, Delta δ and Alpha α.
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| Little Dog |
English name for the constellation Canis Minor.
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| Little Dumbbell |
Popular name for M76 NGC 650, a planetary nebula in Perseus. It is the faintest object in the Messier Catalogue.
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| Little Green Men |
A name given by Jocelyn Bell Burnell to the first four pulsars discovered before their nature as rotating neutron stars was known.
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| Little Horse |
English name for the constellation Equuleus.
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| Little Lion |
English name for the constellation Leo Minor.
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| Lizard |
English name for the constellation Lacerta.
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| Lm |
Abbreviation for Lunar Module, a term used to describe part of the craft used in the Apollo programme of Moon landings.
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| Lmc |
Abbreviation for Large Magellanic Clouds.
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| Lmst |
Abbreviation for local mean solar time.
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| Local Bubble |
A low-density region of the interstellar medium within which the Sun is located. At the boundary of the bubble, the gas density rises sharply by a factor of at least 10. The bubble boundary is nearest to the solar system in a direction roughly towards the galactic centre, where an extended dust cloud known as Tinbergen’s Cloud lies about 30 light years away. The nature of this cloud is not well understood but it appears that its relative motion has led to a considerable deformation of the Local Bubble. The furthest extent of the bubble is about 500 light years away in the direction of the constellation Canis Major, where the bubble wall is permeated by tunnel-like structures. The Local Bubble was probably blown out by the shock wave from one or more supernova explosions that took place in our part of the Galaxy in the remote past.
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| Local Cloud |
A small diffuse cloud of interstellar material in which the Sun is embedded. It is about 20-30 light years across and the Sun is located towards one edge. The Local Cloud lies within the Local Bubble.
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| Local Group |
An assembly of galaxies to which our own Milky Way Galaxy belongs. The dominant members are the Andromeda Galaxy M31, which is the largest and most massive, and our own Galaxy. Next in size are the spiral galaxy in Triangulum, M33, which is a near companion of M31, and the Large Magellanic Cloud, near our Galaxy. The other members of the Local Group are small elliptical and irregular galaxies plus a number of dwarf spheroidal galaxies, resembling isolated globular clusters. These dwarf galaxies are so faint, it is very difficult to detect them at distances greater than the Andromeda Galaxy, so the total number is unknown. The four small elliptical galaxies NGC 221, 205, 185 and 147 are satellites of M31; the Magellanic Clouds and various dwarf galaxies are satellites of our own. Thus the Local Group does not have a central condensation, but two subgroups centred around the two most massive members.
The Local Group occupies a volume of space with a radius of about 3 million light years 1 megaparsec. The next nearest galaxies are two or three time this distance away.
See also: Maffei galaxies.
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| Local Hour Angle Lha |
The hour angle of a celestial object as measured by an observer at a particular locality. The local hour angle of an object at any instant varies according to the longitude of the observer.
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