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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| Hydroxyl |
OH source, maser.
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| Hydrus The Water Snake |
An inconspicuous southern constellation, introduced by Johann Bayer in his 1603 star atlas. Its three brightest stars are third magnitude.
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| Hygeia |
Asteroid 10, diameter 430 km, discovered by A. de Gasparis in 1849. It is the fourth-largest asteroid.
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| Hyperbolic |
Having the shape of a hyperbola, one of the family of curves known as conic sections. The hyperbola is one of the possible shapes for the orbit of a body under the influence of a central gravitational force. The hyperbolic shape results if the body has enough energy to be able to escape from the gravitational force. A body travelling fast enough for this to occur is sometimes described as having a hyperbolic velocity.
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| Hyperbolic Space |
space that has negative curvature and within which the angles of a triangle add up to less than 180°. The surface of a saddle is a two-dimensional example.
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| Hypergalaxy |
A group of galaxies consisting of a dominating spiral galaxy surrounded by a cloud of dwarf galaxies. Our own Galaxy and the Andromeda Galaxy are examples.
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| Hyperion |
A satellite of Saturn, discovered in 1848 by W. C. Bond. It is an elongated irregular body measuring approximately 350 × 200 kilometres. There are large craters and a curving scarp-like feature, apparently 300 kilometres long. The evidence suggests that it may be a remnant of a larger body shattered by an impact.
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