Astronomical Unit (AU) The Astronomical Unit is the average distance between the Sun and the Earth. Distance to nearby stars is generally expressed in light years and parsecs while the distance to galaxies is expressed in kilo-parsecs and mega-parsecs. To describe the distance to planets in the solar system, we generally use AU. A star is one parsec (pc) away from the Earth if the parallax angle is 1 arcsecond. The usage of the units depends on the range of distance. No information on contributors is available for this page. A parsec is an astronomical unit of distance. Monthly Notices of the Royal Astronomical Society, vol 4, no. A parsec is a unit of distance that is often used by astronomers as an alternative to the light-year, just as kilometers can be used as an alternative to miles. We thank Ken Croswell for calling this article to our For even greater distances, astronomers use kiloparsecs and megaparsecs (abbreviated kpc and Mpc). Publications of the Astronomical Society of the Pacific, volume 25, A parsec is the distance at which 1 AU subtends an angle of 1 arcsec. London: Imperial College Bookstall, no date. Transactions of the International Astronomical Union. Proceedings of the National Academy of Sciences, volume 6, page 360 ( 1920).įirst General Assembly, held at Rome, May 2nd to May 10th, 1922. The parallax of a star was first successfully measured in 1837,ġ. This angle is very small only 1″.5 for the It is the distance that light travels in 3.26 years, or just under 31 trillion kilometres (about 19 trillion miles). What is a parsec in simple terms A parsec is a unit of distance used in astronomy. The size of the jump can be expressed as the angle between A parsec amounts to about 3.26 light-years, or about 19.2 trillion miles (30.9 trillion kilometers). Your finger did, a nearby star will appear to jump against the background of Six months apart, so that the positions are at opposite sides of Earth's orbit. In place of your two eyes, astronomers use two positions of the earth, This phenomenon can be used to measure the distance to stars that are not tooįar away. Nearer your finger is to your face, the bigger the jump appears to be. The finger appears to jump against the background something else appears behind The parsec is based on the phenomenon called parallax. In 1922, the Commission des notations, des unités et de l'économie des publications of the International Astronomical Union accepted, and the First General Assembly adopted, the recommendation of an American committee¹ that distances to stars be described in parsecs.² In the early 1900s, the parsec was also known as the macron, astron, and astrometer.³ What is parallax? The greater the parallax, the smaller the distance. One parsec is the distance from Earth to a star that shows a parallax of one second of arc. Convert between parsecs and other major units of astronomical distance.Ī unit of distance used in astronomy.
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