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length comparison table

Subject	has unit	has uncertainty	has definition	has equation	has symbol	has value	is a component of	see also	is requir	is a kind of	applies to	is an instance of
distance	length unit		The distance to a celestial object measured from the center of the Earth or Sun, in units of parsec or lightyear				equatorial coordinate					length
Galactocentric distance	length unit		A star's distance from the Galactic center. The Sun's Galactocentric distance is about 27000 light-years.				astronomical coordinate					length
height	length unit		Elevation above ground or distance upwards from a given level (especially sea level) to a fixed point. (See altitude.)				geocentric coordinate					length
mean free path	length unit		The mean distance traversed by a particle before undergoing a significant deflection or collision.							length
particle Compton wavelength	m		The wavelength of a photon containing the rest energy of a particular particle.	h bar / mc, where h bar is Plancks constant, c is the speed of light, and m is the particle mass.		changes in value are due solely to an increase in measurement accuracy or convention				length	particle
Planck length	length unit	0.0012 × 10-35 m	The scale below which quantum fluctuations in the fabric of spacetime would become enormous. The size of a typical string in string theory.		lP	1.6160 × 10-35 m						length
radius	length unit									length
semimajor axis	length unit		An orbital element representing half the length of the major axis of an ellipse.		a			osculating element	to define the size, shape, and orientation of an orbit in space			length
semiminor axis	length unit		Half the length of the minor axis of an ellipse; a standard element used to describe an elliptical orbit.									length

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