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abstraction > mathematical concept > number > quantity > length

length
subject			fact

length	has unit length unit
	is a kind of quantity
number	has value

Kinds of length :

• distance (3 facts) - The distance to a celestial object measured from the center of the Earth or Sun, in units of parsec or lightyear
• Galactocentric distance (3 facts) - A star's distance from the Galactic center. The Sun's Galactocentric distance is about 27000 light-years.
• height (3 facts) - Elevation above ground or distance upwards from a given level (especially sea level) to a fixed point. (See altitude.)
• mean free path (3 facts) - Mean length of the path of a particle between collisions., The mean distance traversed by a particle before undergoing a significant deflection or collision.
• particle Compton wavelength (5 kinds, 35 facts) - The wavelength of a photon containing the rest energy of a particular particle.
• Planck length (9 facts) (l_P) - The dimension at which space is predicted to become "foamlike" and at which Einstein's theory is supposed to break down., The size limit at which normal notions of space-time are supposed to break down., The scale below which quantum fluctuations in the fabric of spacetime would become enormous. The size of a typical string in string theory.
• radius (8 kinds, 35 facts)
• semimajor axis (4 facts) (a) - An orbital element representing half the length of the major axis of an ellipse.
• semiminor axis (2 facts) - Half the length of the minor axis of an ellipse; a standard element used to describe an elliptical orbit.