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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.
Twilight
Twilight, the light diffused over the sky from sunset to darkness and from darkness to sunrise.
See more »Unidentified Flying Object
Unidentified Flying Object, or UFO, an object or light that cannot be readily explained as being man-made or of natural origin.
See more »Universe
Universe, in astronomy, all matter and energy whose existence has been, will be, or could be made known to us.
See more »Van Allen Radiation Belts
Van Allen Radiation Belts, two zones encircling the earth in which there are relatively large numbers of high-energy (fast-moving) charged particles.
See more »Week
Week, a cycle of days used in reckoning time. In the Gregorian calendar a week consists of seven days and begins with Sunday.
See more »What is a light year?
A light year is a way of measuring distance. That doesn't make much sense because "light year" contains the word "year," which is normally a unit of time. Even so, light years measure distance.
See more »Winter
Winter, the cold season of the year. Astronomically, in the Northern Hemisphere winter begins at the winter solstice, about December 22, and ends at the spring equinox, about March 21.
See more »Year
Year, a unit of time. It is based on the time it takes the earth to make one revolution around the sun.
See more »Zodiac
Zodiac, an imaginary belt in the sky extending some 8 on either side of the ecliptic, the apparent annual path of the sun among the stars.
See more »Zodiacal Light
Zodiacal Light, a faint glow that appears along the zodiac above the western horizon after sunset and above the eastern horizon before sunrise.
See more »How does gravity assist with interplanetary satellites?
When satellites go off to places like Jupiter or Saturn (or even out of the solar system), they follow crazy orbits. They will often loop around a planet to get a "gravity assist" or "gravity boost." How does that work? I know the Galileo probe looped around Earth twice to get a boost, and the Pioneer and Voyager probes used Jupiter.
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