![]() This corresponds to the small-angle definition of the parsec found in many astronomical references. In August 2015, the International Astronomical Union (IAU) passed Resolution B2 which, as part of the definition of a standardized absolute and apparent bolometric magnitude scale, mentioned an existing explicit definition of the parsec as exactly 648 000 / π au, or approximately 30.856 775 814 913 673 ×10 15 metres (based on the IAU 2012 definition of the astronomical unit). Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kiloparsecs (kpc) for the more distant objects within and around the Milky Way, megaparsecs (Mpc) for mid-distance galaxies, and gigaparsecs (Gpc) for many quasars and the most distant galaxies. Partly for this reason, it is the unit preferred in astronomy and astrophysics, though the light-year remains prominent in popular science texts and common usage. This distance is referred to as one light year. The word parsec is a portmanteau of "parallax of one second" and was coined by the British astronomer Herbert Hall Turner in 1913 to simplify astronomers' calculations of astronomical distances from only raw observational data. In one Earth year of 364.25 days (8,766 hours), light travels a distance of 5,878,625,370,000 miles (9.5 trillion km). Just type the number of light years into the box and hit the Calculate button. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (not to scale) Use this easy and mobile-friendly calculator to convert between light years and parsecs. You can find a full list of credits here. ![]() 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. The OAE Multilingual Glossary is a project of the IAU Office ofĪstronomy for Education (OAE) in collaboration with the IAU Office of Astronomy This term and its definition have been approved by a research astronomer and a teacher Even Proxima Centauri, the closest star apart from our Sun, has a parallax of less than 1 arcsecond. Sirius is 2.7 pc distant from us, corresponding to a parallax of 1/2.7=0.37 arcseconds. Its direct geometrical meaning makes the parsec the professional astronomer's preferred measure of distance, more common in the literature than distances given in light-years. This results in a simple relationship: the distance in parsecs is one divided by the parallax angle in arcseconds. ![]() For an astronomical object at a distance of one parsec, a change in observer position by one astronomical unit (usually because the Earth has moved along its orbit between the two observations) corresponds to an apparent position shift, called the object's parallax (angle), of one arcsecond. ![]() For this method, one measures tiny position shifts of astronomical objects in the sky as the observer position changes by a given length. The practical importance of this definition is its relation to the parallax method of distance determination. This makes 1 pc equal to approximately 3.26 light-years, and to as many astronomical units as there are arcseconds in one radian: 206264.8 astronomical units. From a distance of exactly one parsec, we will see the circle's radius subtend an angle of one arc second. ![]() A parsec is defined as the distance that an object would have to be from the sun to have a parallax angle of 1' (one arc-second). Parsecs are the preferred unit used by astronomers when talking about distances. Description: The parsec (pc) is a standard unit of distance measure in astronomy, defined as follows: Imagine a circle with a radius of one astronomical unit (which is the average Earth-Sun distance), which we are viewing face-on. It is approximately equal to 3.3 light years. ![]()
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