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abstraction > mathematical concept > number > quantity > orbital quantity > orbital element > epoch

epoch comparison table

Subject	is an instance of	has unit	is a kind of	see also	has symbol	has definition	is requir
orbital element			orbital quantity	osculating element		One of seven quantities that must be established from observations in order to define the size, shape, and orientation of an orbit in space.	to define the size, shape, and orientation of an orbit in space
time		time unit	quantity			A dimension distinguishing past, present, and future. In relativity, time is portrayed as a geometrical dimension, analogous to the dimensions of space.
epoch	time	time unit		osculating element	T	A date and time that specifies the reference system to which celestial coordinates are referred. Prior to 1984 coordinates of star catalogs were commonly referred to the mean equator and equinox of the beginning of a Besselian year. Beginning with 1984 the Julian year has been used, as denoted by the prefix J, e.g., J2000.0.	to define the size, shape, and orientation of an orbit in space

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