General astronomy

General astronomy

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General astronomy

secular motion

Astronomy; General astronomy

Secular variations in the motions of the planets are those that have very slow changes that proceed through ages (''secula'') in a way such that they are nearly proportional with time for a ...

The change of a solid (such as ice) directly into a gaseous state (bypassing the liquid state). This happens in the vacuum of space with comets, as the heating effects of solar radiation cause ices ...

heliocentric

Astronomy; General astronomy

Referring to the sun. A heliocentric orbit is one based on the sun as one of the two foci of the (elliptical) orbit (or as the center of a circular orbit); a heliocentric magnitude is the brightness ...

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 ...

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 ...

julian date (JD)

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 ...

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 ...