General astronomy

General astronomy

Contributors in General astronomy

General astronomy

The interval of time in days (and fraction of a day) since Greenwich noon on Jan. 1, 4713 BC. The JD is always half a day off from Universal Time, because the current definition of JD was introduced ...

extinction, atmospheric

Astronomy; General astronomy

The diminishing of light from astronomical objects due to the earth's atmosphere, in which molecules (air, dust, etc.) of the atmosphere absorb, reflect, and refract light before it reaches the ...

equinox

Astronomy; General astronomy

Either of the two points (vernal, autumnal) on the celestial sphere where the ecliptic (which is the apparent path of the sun on the sky) intersects the celestial equator. Due to precession, this ...

ephemeris time (ET)

Astronomy; General astronomy

Determined in principle from the sun's apparent annual motion, ET is the numerical measure of uniform time, which is the independent variable in the gravitational theory of the earth's orbital ...

ephemeris

Astronomy; General astronomy

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 declination ("Decl. " in these web pages), ...