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time comparison table

Subject	has equivalent	has uncertainty	has equation	has definition	has value	has symbol	see also	has synonym	is requir	is a kind of	has accuracy	is an instance of
crossing time				The time it takes a particle to travel from one point in its orbit to another point 180° away.								time
delay time				Time lapse between the time a signal (e.g., a radar beam) is propagated out to a distant object and the time it is received after the object bounces it back.								time
epoch				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.		T	osculating element		to define the size, shape, and orientation of an orbit in space			time
half-life				Time it takes for the number of particles to halve. For a radioactive substance, the length of time required for half the atoms to disintegrate.		τ1/2	mean life			time
hold-time				The time taken to use up all the liquid cryogens, like LN2, in a cooled CCD cryostat.								time
Hubble time				The inverse of the Hubble constant and a crude measure of the universe's age. For a Hubble constant of 50, one can calculate that the Hubble time is 19.6 billion years; for a Hubble constant of 80, the Hubble time is 12.2 billion years. If there is no cosmological constant, the universe is younger than the Hubble time. In particular, if the mass density of the universe (designated Ω) is 0.1, the universe's age is 90 percent of the Hubble time; if Ω is 1.0, the universe's age is 67 percent of the Hubble time.	10 to 20 billion years	H0-1						time
integration time				The interval of time used to collect photons of light on a detector and build-up a strong signal.								time
Kelvin timescale				The time it takes a star to contract gravitationally from infinite radius down to its present radius by radiating its thermal energy.	(gravitational binding energy) / luminosity		nuclear time scale			time
lifetime	half-life / ln 2			The time it takes for a sample of identical particles to decay to 1/e of its initial population.		τ	half-life	mean life		time
lookback time				The time in the past at which the light we now receive from a distant object was emitted. Galaxies of a certain type (redshift and luminosity) can be seen only at a certain distance.								time
nuclear time scale				Time required for a star to evolve a significant distance off the main sequence; the time it takes a star to convert all its available hydrogen into helium.			Kelvin timescale			time
period				An orbital element representing the time required to complete an orbit. This parameter is required when determining the orbit of a binary star system in which the mass is not known.		P	osculating element		to define the size, shape, and orientation of an orbit in space			time
Planck time		0.0040 × 10-44 s			5.3906 × 10-44 s	tP						time
rise time				The time required for the vehicle to achieve its optimum height (in rocket or balloon astronomy).								time

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