A parallax is when a foreground object moves compared to a more distant background. For the vast gulfs between galaxies, astronomers use kiloparsecs, megaparsecs and even gigaparsecs (feel small yet?).Ī parsec is defined as: "the distance corresponding to a parallax of one arcsecond." While that might read like absolute gibberish, there is a rational explanation. Yet, for the distance between stars outside of our solar system, a larger unit is necessary.
In our solar system, kilometers or astronomical units tend to get the job done in measuring distance in space. The parsec (pc) is an astronomical unit of length, equal to the distance at which the radius of Earths orbit subtends an angle of one arcsecond (Fig 1). A light-year (also light year or lightyear, ly), is a non-SI unit of length equal to just under 10 trillion kilometers or about 6 trillion miles or 0.306. This is from the definition: a parsec is the distance from the Sun to an object which has a parallax angle of one arcsecond.The technique used in the calculation is trigonometry. While it might not seem like a lot, it might help to put it in perspective: it would take photons of light three years to travel one parsec's distance. A parsec is a unit of distance used in astronomy.It is the distance that light travels in 3.26 years, or just under 31 trillion kilometres (about 19 trillion miles). Photo credit: Pinterest.Īlso equivalent to 3.26 light-years, a parsec is a nearly unimaginable distance packaged in palatable terms. One parsec is equal to about 31 trillion kilometers, and most of the stars visible to the unaided eye in the night sky are within 500 parsecs of our sun. Parsecs measure extremely long distances to astronomical objects outside of our solar system. In astronomy, which of the following units of measurement is the longest?Ĭonsidering gigametre, light-year, parsec and lunar distance, the answer is: parsec.Ĭontrary to what Han Solo says in Star Wars, a parsec is a distance, not a unit of time.
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