Units of measurement in astronomy

A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Despite its inclusion of the word "year", the term is not a unit of time.

mean distance between Earth and the Sun, common length reference in astronomy

The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 au subtends an angle of one arcsecond ( of a degree). The nearest star, Proxima Centauri, is about from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant a

standard unit of mass in astronomy which is equal to 1.98892 × 10³⁰ kg

unit of measurement

logarithmic measure of the brightness of an astronomical object

unit of mass equal to that of Earth

unit of radiant flux in astronomy

intensity of sunlight

mass of planet Jupiter, used as unit of mass

unit of a quantity of 1,000,000 years

mean distance from the Earth's center to its surface

measure of hazard posed by near-Earth objects

The light-second is a unit of length useful in astronomy, telecommunications and relativistic physics. It is defined as the distance that light travels in free space in one second, and is equal to exactly (approximately or ).

distance from center of Earth to center of Moon

The jansky (symbol Jy, plural janskys) is a non-SI unit of spectral flux density, or spectral irradiance, used especially in radio astronomy. It is equivalent to 10−26 watts per square metre per hertz.

unit of radius equal to the total radius of the planet Jupiter

system of measurement developed for use in astronomy

type of constant

meteor shower

astrophotometrical unit for x-ray sources

measure of the mass of a planet-like object