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astronomy terms library
Astronomy terms are used to describe the various phenomena in space. In this section you can learn what every astronomy term means and how it helps us to better understand the cosmos.
Ecliptic
Ecliptic, the apparent annual path of the sun among the stars. The sun appears to follow a path through the stars because the earth revolves around the sun.
See more »Epoch (Chronology)
Epoch, in chronology (timekeeping), a point in time, such as 302 B.C. or October 30, 1936, or 7:34 A.M.
See more »Equinox
Equinox, During the course of a year, the sun appears to move northward for about six months and southward for about six months.
See more »Eros (asteroid)
Eros, a small asteroid (minor planet) discovered in 1898. It was the first asteroid known to come closer to the earth than the planet Mars.
See more »Evening Star
Evening Star, the name given to any of the five bright planets in the sky at sunset.
See more »Horizon
Horizon, the visible boundary between earth and sky. Because the earth is a globe, its surface curves out of sight.
See more »Hour
Hour, a unit for measuring time, defined as either 1/24 of a day or 3600 seconds (60 minutes).
See more »Hourglass
Hourglass, a device for measuring time. In its usual form it consists of two cone-shaped or oval glass receptacles joined by a narrow neck.
See more »How many teaspoons are there in a cubic light year?
Have you ever really thought about the scale of the universe? A good starting point is the teaspoon.
See more »If you were to move all of the matter in the universe into one corner, how much space would it take up?
If you took all of the matter in the universe and you pushed it all into one corner, how much space would it take up? I am trying to understand how much of the universe is 'empty.'
See more »Interferometer
Interferometer, an instrument that uses the interference patterns formed by waves (usually light, radio, or sound waves) to measure certain characteristics of the waves themselves or of materials that reflect, refract, or transmit the waves.
See more »Magellanic Clouds
Magellanic Clouds, three irregularly shaped galaxies that lie some 150,000 to 200,000 light-years from earth.
See more »Magnitude
Magnitude, in astronomy, a unit of measurement of the brightness of stars. The scale of magnitude extends from negative numbers (for example, the minus first magnitude) for very bright stars to positive numbers (for example, the fourth magnitude) for dimmer ones.
See more »Meteor
Meteor. As the term is commonly used, a meteor is a small celestial body that enters the atmosphere of the earth.
See more »Meteorite
Meteorite, a meteor that reaches the earth's surface. Meteors are naturally occurring objects that enter the earth's atmosphere from space, traveling at high speed.
See more »Midnight Sun
Midnight Sun, a name given the sun when it can be seen at midnight during the Arctic or Antarctic summer.
See more »Millennium
Millennium, in a common Christian belief, the period of 1,000 years before the Last Judgment, during which time Christ and the saints will reign on earth.
See more »Minute
Minute, a unit for measuring both time and space. As a unit of time, a minute is 60 seconds, or 1/60 of an hour.
See more »Month
Month, a unit of time. The calendar month is approximately 1/12 of the calendar year.
See more »Nebular Hypothesis
Nebular Hypothesis, an explanation of how the solar system was formed, proposed by Pierre Simon de Laplace in 1796.
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