Parsec is a unit that astronomers use to measure extremely long distances, such as the distance between stars. A parsec equals 3.26 light-years, or 19.2 trillion miles (30.9 trillion kilometers). A light-year is the distance that light travels in a vacuum in a year. That distance equals about 5.88 trillion miles (9.46 trillion kilometers).
The word parsec is a combination of the words parallax and second. The second is an angle equal to 1/3,600 degree. In astronomy, parallax is the angle between the straight lines that join a star or another celestial object to different points of observation. The parallax equals the difference between the directions in which the object is seen. The parsec is based on what the parallax of a certain imaginary object would be if observed from opposite sides of Earth’s orbit. If the parallax were one second, the distance from the center of Earth’s orbit to the object would be 1 parsec.
See also Parallax .
