General astronomy

General astronomy

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General astronomy

x-ray

Astronomy; General astronomy

Electromagnetic radiation of a very short wavelength and very high-energy. X-rays have shorter wavelengths than ultraviolet light but longer wavelengths than cosmic rays.

Supernova

Astronomy; General astronomy

A supernova is a cataclysmic explosion caused when a star exhausts its fuel and ends its life. Supernovae are the most powerful forces in the universe. All of the heavy elements were created in ...

When the Plough and Cassiopeia are known, we have two valuable guides one to each side of the Pole, and two more are given by the bright stars Vega and Capella, one on each side of a line drawn from ...

terrestrial Dynamical Time (TDT or TT)

Astronomy; General astronomy

Time scale used in orbital computations; TDT is tied to atomic clocks (International Atomic Time, TAI), whereas Universal Time is tied to observations. Prior to 1992, Ephemeris Time (ET) was used in ...

universal Time (UT, or UTC)

Astronomy; General astronomy

A measure of time used by astronomers; UT conforms (within a close approximation) to the mean daily (apparent) motion of the sun. UT is determined from observations of the diurnal (daily) motions of ...

ephemeris (plural: ephemerides).

Astronomy; General astronomy

Pronounced ee-FEM-er-is (ef-fi-MARE-uh-deez). A table listing specific data of a moving object, as a function of time. Ephemerides usually contain right ascension ("R.A." in these web pages) and ...

light pollution

Astronomy; General astronomy

The emission of stray light or glare from lighting fixtures in manners that counter the purpose of the light (which is to light what is below); also known as the waste of money and energy in the form ...