Glossary -- L

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latitude

used to specify position on the Earth, it is the number of degrees north or south of the Earth's equator.

law of gravity

(Newton's): the force of mutual attraction between two objects = G×(mass #1) × (mass #2) / (distance between the objects)². The term G is a universal constant of nature that always = 6.672× 10^-11 meter³/(kilogram second²).

life zone

the region around a star where the temperature on a planet's surface is between the freezing point (0° C) and boiling point (100° C) of water.

light curve

a plot of how an object's brightness changes over time.

light-gathering power

the ability of a telescope to collect more light than the human eye in a given amount of time. It depends on the area of the telescope's objective, such that the larger the collecting area of the objective, the brighter the image will be.

lighthouse model

a model describing how pulsars pulsate: the rapidly rotating neutron star produces a narrow beam of light from its magnetic field and if the magnetic pole is aligned with the Earth, the narrow beam of light sweeps over us periodically like the beam of a lighthouse does for ships at sea.

light year

distance light travels in one year (9.461 trillion kilometers, over 63,000 A.U.!). Used for interstellar distances.

line of nodes

the intersection of a planet's or the Moon's orbit with the Earth's orbit.

local noon

when the Sun is on an observer's meridian.

long period comet

a comet with an orbit period of thousands to millions of years long that comes from the Oort cloud.

longitude

used to specify position on the Earth, it is the number of degrees east or west of the 0° line going through Greenwich, England.

luminosity

the total amount of energy radiated by an object every second.

lunar eclipse

when the shadow of the Earth hits the Moon at exactly full phase.

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last update: 06 August 1999