ASTR 103 - Astronomy

Glossary - L

Lagrangian points

 

law of areas

Kepler's second law of planetary motion. The straight line connecting the Sun and an orbiting planet sweeps out equal areas in equal intervals of time.

law of elliptic orbits

Kepler's first law of planetary motion. Each planet moves around the Sun in an ellipse with the Sun at one focus of the ellipse.

leptons

Class of light elementary particles that constitute the electrons, muons, and their associated neutrinos.

Light

 

light curve

plot that shows the change in the magnitude of a variable star (plotted vertically) versus the time (plotted horizontally).

light year (ly)

Distance that light travels in one year. Its value is 9.46 x 10¹² kilometers.

limb

Edge of the apparent disk of a celestial body.

limb darkening

 

line of nodes

 

liquid

That particular state of matter in which the constituent particles maintain only a temporary relation to each other.

Lithosphere

Stony crust and upper mantle of Earth to an approximate depth of 50 kilometers.

Local Group

Small group of bunched galaxies, including our Galaxy, consisting of about 20 known members spread over a diameter of about three million light years.

Local Supercluster

Observed clumping of a supersystem of galaxies scattered over a volume of space about 130 million light years in diameter. The Local Group is one subunit of the supercluster.

long-period comet

Comet whose orbital period is greater than about 200 years.

long-period variable

Red variable star with an amplitude variation of several magnitudes over a period between approximately 200 to 400 days.

Lorentz contraction factor

The term 1-(v²/c²), first introduced by the Dutch physicist H.A. Lorentz. It appears in the formulas for relativistic length, mass and time intervals.

luminosity

 

luminosity class

One of the divisions (Ia, Ib, II, III, IV, V) into which the stars are arranged according to their luminosity and spectral class.

luminosity function

Relative number of stars of a specific absolute magnitude in a given volume of space.

lunar eclipse

 

Lyman series

Ultraviolet hydrogen series of spectral lines arising from transitions to or from the ground level of the atom.