AstroGlossary - L
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
light
Electromagnetic radiation of all wavelengths and frequencies. The familiar "rainbow" of light spans a narrow slit in the electromagnetic spectrum, from 700 nanometers (red) to 400 nanometers (blue). The wavelengths of red and blue light differ by less than a factor of two. The electromagnetic spectrum range spans beyond a factor of 10^18, (1 followed by 18 zeroes) from radio to gamma ray wavelengths. Radio wavelengths can be the size of mountains while gamma ray wavelengths are the size of an atomic nucleus. light curve
Brightness or intensity of light plotted against time on a graph. Astronomers discover dark stellar companions using the light curve of the star. As a dark orbiting object eclipses the star, the brightness falls, producing a dip on the light curve. Careful analysis of the light curve reveals the masses of the star and dark companion plus the distance to this eclipsing binary system. light-gathering power
A measure of a telescope's ability to collect light. Light gathering power is proportional to the telescope's lens or mirror surface area. Astronomers enjoy observing through large aperture telescopes because they may see faint, distant objects and detail of nearby objects. light-year
A unit of length used by astronomers to measure distance. One light-year is equal to the distance light travels in one year, which is about 5.88 trillion miles or almost 800 times the diameter of our solar system. The nearest star is 4.2 light-years away, while the nearest spiral galaxy lies about 2.5 million light-years from Earth. Local Group
Our galactic neighborhood, including the Milky Way, Andromeda Galaxy, M33, and more than 30 smaller galaxies. The Local Group appears to be a suburb of a supercluster of galaxies that lies 60 million light-years away, known as the Virgo Supercluster. luminosity
A measure of the rate of energy flowing from a source, like a galaxy, star, or light bulb. Luminosity tells astronomers how fast energy "leaks" from the star. Luminosity is a measure of power divided into units called watts. Given the luminosity of a star, an astronomer can calculate the distance to the star by measuring the star's brightness. Temperature and luminosity are related, but dependent on the mass and size of a star. See also: temperaturelunar eclipse
A spectacular, though relatively common, celestial event that occurs when the Moon, Earth and Sun form a line in space. The Moon travels through Earth's shadow. lunar phases
The apparent shapes of the Moon as seen from the Earth, which are caused by the Moon's orbit of the Earth once every 29.5 days. The same phase will fall on the same date of the year according to the Saros cycle, every 18 years, 11 days, and eight hours. The phases of the Moon are:
New Moon
In conjunction with the Sun; rises and sets with it. Zero percent illuminated, 0 degrees elongation.
Waxing Crescent
Prominent just after sunset; less than 50 percent illumination.
First Quarter
Rises at noon and sets at midnight; 50 percent illuminated, 90 degrees east elongation.
Waxing Gibbous
Lunar illumination increasing between first quarter and full.
Full Moon
In opposition with the Sun; rises at sunset and sets at sunrise; 100 percent illuminated, 180 degrees elongation.
Waning Gibbous
Decreasing illumination decreasing between full and last quarter.
Last Quarter
Rises at midnight and sets at noon; 50 percent illuminated, 90 degrees west elongation.
Waning Crescent
Prominent just before sunrise; less than 50 percent illumination.
|
  |
Contact StarDate | About StarDate | Friends of McDonald | Sign up for Sky Tips
