Kepler's Laws of Planetary Motion Three laws which summarize the motions of the planets about the Sun, or more generally, the motion of one body around another under the influence of gravity.
Kerr black hole A rotating black hole.
kiloelectron volt A unit used to describe the energy of X-rays, equal
to a thousand electron volts.
kilometer A unit of distance equal to 0.6214 mile.
kinetic energy The energy of an object due to its motion.
light curve The variation in brightness of a star with time.
lighthouse model The leading explanation for pulsars. A small region of the neutron star, near one of the magnetic poles, emits a steady stream of radiation which sweeps past Earth each time the star rotates. Thus the period of the pulses is just the star's rotation period.
light year The distance that light, moving at a constant speed of 300,000km/s, travels in one year. One light year is about 10 trillion kilometers.
Local Group The small galaxy group that includes the Milky Way Galaxy, the Andromeda Nebula, and about 20 smaller galaxies.
luminosity One of the basic properties used to characterize stars, luminosity is defined as the total energy radiated by a star each second, at all wavelengths.
luminosity class A classification scheme which groups stars according to the width of their spectral lines. For a group of stars with the same temperature, luminosity class differentiates between supergiants, giants, main-sequence stars and subdwarfs.
K
Kelvin temperature scale An internationally agreed upon temperature scale, equal to the Celsius (or centigrade) scale plus 273 degrees; hence water freezes at 273 kelvins and boils at 373 kelvins.
L
Lagrange point One of five special points in the plane of two massive bodies orbiting one another, where a third body of negligible mass can remain in equilibrium.