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Laplace, Pierre Simon, marquis de

(Encyclopedia)Laplace, Pierre Simon, marquis de pyĕr sēmôNˈ märkēˈ də läpläsˈ [key], 1749–1827, French astronomer and mathematician. At 18 he went to Paris, proved his gift for mathematical analysis to...

Brahe, Tycho

(Encyclopedia)Brahe, Tycho tīˈkō brä [key], 1546–1601, Danish astronomer. The most prominent astronomer of the late 16th cent., he paved the way for future discoveries by improving instruments and by his prec...

tektite

(Encyclopedia)tektite tĕktīt [key], naturally occurring, silica-rich (65%–80% SiO2) glass resembling obsidian and sometimes shale, and is normally jet black to olive green. They appear as small rounded or elong...

Van Allen, James Alfred

(Encyclopedia)Van Allen, James Alfred, 1914–2006, American physicist and space scientist, Mt. Pleasant, Iowa. A graduate (Ph.D 1939) of and professor of physics (1951–85) at what is now the Univ. of Iowa, where...

United States Naval Observatory

(Encyclopedia)United States Naval Observatory, a federal astronomical observatory, located in Washington, D. C. It evolved from the Navy's oldest scientific institution, the Depot of Charts and Instruments, founded...

Tethys , in astronomy

(Encyclopedia)Tethys tēˈthĭs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn III (or S3), Tethys is 659 mi (1060 km) in diameter, orbits Saturn at a mean dista...

seeing

(Encyclopedia)seeing, in astronomy, the clarity with which stars and other celestial objects can be observed. It is primarily determined by the atmosphere of the earth. The most obvious phenomenon is twinkling, whe...

Sirius

(Encyclopedia)Sirius sĭrˈēəs [key], or Dog Star, brightest star in the sky. It is located in the constellation Canis Major (1992 position R.A. 6h44.8m, Dec. −16°42′); its Bayer designation is Alpha Canis M...

time , sequential arrangement of all events

(Encyclopedia)time, sequential arrangement of all events, or the interval between two events in such a sequence. The concept of time may be discussed on several different levels: physical, psychological, philosophi...

Easter

(Encyclopedia)Easter [A.S. Eastre, name of a spring goddess], chief Christian feast, commemorating the resurrection of Jesus after his crucifixion. In the West, Easter is celebrated on the Sunday following the full...