Glossary term: Parsec

Description: The parsec (pc) is a standard unit of distance measure in astronomy. One parsec is the distance to a point in space that subtends a parallax angle of one arcsecond. This gives the relationship: distance, d (in parsecs) = 1 / parallax angle, p (in arcseconds). By measuring the parallax of a star astronomers can directly determine the distance to it. Even the closest star other than our Sun has a parallax of less than 1 arcsecond. A parsec is approximately equal to 3.26 light years. Astronomers use the parsec instead of light years because the parsec is directly determined from geometry and trigonometry. It is not dependent upon an arbitrary time scale. If it is possible to measure an object's parallax, its distance can be directly determined. Sirius is 2.7 pc distant from us.

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The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".