General astronomy

General astronomy

Contributors in General astronomy

General astronomy

The point on the celestial sphere where the sun crosses the celestial equator moving northward, which corresponds to the beginning of spring in the northern hemisphere and the beginning of autumn in ...

universal time (UT)

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 ...

total (visual) magnitude

Astronomy; General astronomy

Total, integrated magnitude of a comet's head (meaning coma + nuclear condensation). This can be estimated visually, as the comet's "total visual magnitude". The variable m1, usually found in comet ...

terrestrial dynamical time (TDT)

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 ...

sublimation

Astronomy; General astronomy

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 ...

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 relatively ...