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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| Flat |
A plane mirror, optically figured to be flat with a high degree of accuracy.
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| Flatness Problem |
The problem of explaining, in the standard Big Bang models, why the universe as observed has a density so close to the critical density. This means that it is expanding at a rate close to its escape velocity, and its geometry is very nearly that of Euclidean space. The problem is resolved by inflationary universe models.
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| Flexus Pl. Flexi |
A type of cusped linear feature on the surface of Europa.
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| Flocculi Sing. Flocculus |
A fine mottled pattern seen on the Sun when the solar chromosphere is imaged in monochromatic light, such as the light of singly ionized calcium.
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| Flora |
Asteroid 8, diameter 162 km, discovered by J. R. Hind in 1847.
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| Flora Group |
A complex grouping of asteroids near the inner edge of the asteroid belt at a distance of 2.2 AU from the Sun. The group is separated from the main belt by one of the Kirkwood gaps and is not a true family with a common origin.
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| Fluctus Pl. Fluctus |
Terrain on the surface of Io where flow of molten material has taken place.
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| Flux Collector |
A telescope designed solely to collect radiation in order to measure its intensity or to carry out spectral analysis. No attempt is made to form an image, so a flux collector can have a more crudely figured reflecting surface than a conventional telescope.
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| Flux Density |
The energy in a beam of radiation passing through unit area normal to the beam in one unit of time. In radio astronomy, flux density, measured in janskys Jy, is the energy received from a radio source per unit area of detector per unit frequency interval.
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| Fly |
English name for the constellation Musca.
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| Flyby |
A space mission in which an exploratory probe carries out imaging and other experiments as its flight path passes close to the body under investigation, without landing or going into orbit.
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| Flying Fish |
English name for the constellation Volans.
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| Foal |
English name for the constellation Equuleus.
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| Focal Length Symbol F Or F |
The distance between a lens or mirror and the point on the optical axis where parallel rays of light are brought to a focus.
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| Focal Plane |
The surface on which fall the images of all points in the field of view of an optical instrument such as a telescope. This surface may be flat and normal to the optical axis or, as in the Schmidt telescope, curved, in which case the term focal surface is preferable.
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