![]() ![]() The centre of the Milky Way is over 8kpc from the earth.Īstronomy – despite the enormous distance it describes, the parsec is a relatively small unit in astronomical terms.Proxima Centauri – the nearest star to the Earth other than the Sun, is 1.29 parsecs away.Turner’s was accepted – parsec being derived from the definition of the unit as the distance from the sun to an astronomical object which has a parallax angle of one arcsecond. A unit of distance useful in astronomy had been defined but was without a name, and the Astronomer Royal appealed for suggestions. The term parsec was coined by British astronomer Herbert Hall Turner in 1913. With the parsec defined, deriving and describing huge distances became easy, since a distance i The distance from the Sun of a body with a parallax angle of 1 arcsecond was thus defined as a unit and, thanks to Turner, named the parsec. Once the parallax angle is established you can calculate the distance to a star using trigonometry, because we know Earth’s distance from the Sun. The parallax angle is obtained by halving the angular difference in measurements. The parallax angle is found by measuring the parallax motion (or apparent movement of a star relative to stable, more distant stars) when the star is observed from opposite sides of the Sun (an interval of six months on Earth). The less an object appears to have moved, the farther it is from the Sun, and vice versa.The parsec is a unit of length equivalent to around 20 trillion (20,000,000,000,000) miles, 31 trillion kilometres, or 206,264 times the distance from the earth to the sun.Ī parsec is also equivalent to approximately 3.26 light years (the journey distance if you travelled at the speed of light for three years and three months).Īstronomers used trigonometry to calculate the distance to stars long before the term parsec was coined, but the new unit made it easier to conceptualise unfathomable distances.Ī parsec is the distance from the sun to an astronomical object which has a parallax angle of one arcsecond (1/3600 of a degree). In this case, the object's distance in parsecs is numerically equal to the reciprocal of half the number of arcseconds by which its position appears to change. After six months, the Earth is at the opposite end of its orbit around the Sun, a distance equal to twice the base of the right triangle described above. It becomes quite convenient for astronomers to determine the object's distance by simply measuring its apparent motion in the sky over a 6-month interval. The angle can be measured by observing the object's precise location in the sky. Now, if the angle formed between the line drawn from the object to the Earth and the line drawn from the object to the Sun is exactly one arcsecond, then the object's distance from the Sun would be exactly one parsec. In other words, imagine that a straight line is drawn from the object to the Earth, a second line is drawn from the Earth to the Sun, and a third line is drawn from the object to the Sun that is perpendicular to the line drawn from the Earth to the Sun. This page is about the various possible meanings of the acronym, abbreviation, shorthand or slang term: Planck Length. A parsec is the distance from the Sun to an astronomical object which has a parallax angle of one arcsecond. The name parsec is "an abbreviated form of 'a distance corresponding to a parallax of one arcsecond'." It was coined in 1913 at the suggestion of British astronomer Herbert Hall Turner. ![]() The parsec is a unit of length used in astronomy, equal to about 30.9 trillion kilometres or 3.26 light-years. Freebase (0.00 / 0 votes) Rate this definition: ![]()
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