![]() ![]() A parsec is the length of the long leg of a right triangle, whose short leg is one astronomical unit when the angle between the Sun and the Earth, as seen from an object in space (a star for example), is one arcsecond The word parsec stands for "parallax of one arc second" One kiloparsec (kpc), is one thousand parsecs. The definition of the parsec is based on a triangle. ![]() Parsec (pc) Astronomers use another unit of distance called a parsec (pc), which is equal to 3.26 light-years. Our galaxy, the Milky Way, is about 150,000 light-years across, and the nearest large galaxy, Andromeda, is 2.3 million light-years away. For example, the nearest star to us is about 4.3 light-years away. The speed of light is about 186,000 miles or 300,000 kilometers per second. A light-year (ly) is the distance that light can travel in one year in a vacuum (empty space). ![]() Instead, astronomers measure distances to objects which are outside our solar system in light-years. Light-Year (ly) Most objects in space are so far away, that using a relatively small unit of distance, such as an astronomical unit, is not practical. from the Sun (thats 40 times as far away from the Sun as the Earth is). from the Sun, while the farthest planet, Pluto, is about 40 A.U. For example, the planet Mercury is about 1/3 of an A.U. Astronomical units are usually used to measure distances within our solar system. Astronomical Unit (A.U.) An astronomical unit (A.U.) is the average distance between the Earth and the Sun, which is about 93 million miles or 150 million kilometers. ![]()
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