How big are Parsecs?

                                    Proxima Centauri is the nearest star to the sun at a distance of 4.2 light years or 1.3 parsecs.  Image credit: NASA/ESA

One parsec is equal to 3.26 light years. The nearest star to us, Proxima Centauri, is 4.2 light-years away, or 1.3 parsecs. Converting from light year to parsec is quite simple and all that is needed is to divide the number of light years by 3.26. However, why is one parsec equal to 3.26 light years? Ultimately, this number seems pretty specific. Parsecs are calculated using parallax, which is a form of distance measurement used in astronomical observations. Using parallax, astronomers calculate the distance it takes for one astronomical unit to travel through one second of arc. An astronomical unit equals the distance between the Earth and the Sun, while arcseconds are a unit of angle (one arcsecond equals 1/3600 of a degree). So a parsec is the calculated distance it takes for one astronomical unit of distance to cover an angle of 1/3600 degrees. This distance is 3.26 light years or one parsec.

Larger units of Parsec

                                    Astronomers will generally use megaparsecs or gigaparsecs to measure distances to the most distant galaxies.  Image credit: NASA/ESA

To simplify even longer distances, astronomers also use kiloparsecs, megaparsecs, and gigaparsecs. A kiloparsec is equal to 1,000 parsecs and is generally used to measure distances to objects in and around our Milky Way Galaxy. Megaparsecs are equal to one million parsecs and are used to measure distances to other galaxies. The largest unit, the gigaparsec, is equal to one billion parsecs, and so is used to measure the furthest distances in space.

Units of Distance in Astronomy

            Unit Amount/Definition

Astronomical Unit

93 million miles (150 million kilometers) or the distance between the Earth and the Sun

Lightyear

The distance light travels in one year, equal to 5.88 trillion miles (9.46 trillion kilometers)

Parsec

Distance required by an astronomical unit to cover an angle of one arcsecond, equal to 3.26 light years

Kiloparsec

1,000 parsecs

Megaparsec

A million parsecs

Gigaparsec

A billion parsecs Aidan Remple September 11, 2022 in Science