# How is space measured?

Feb 2, 2017

The universe is measured in Astronomical Units, and Light Years.

#### Explanation:

A Astronomical Unit is the average distance between the Earth and the sun, and as of 2012, it is 149,597,870,700 meters. A light year is the distance light travels in a year, which is about nine trillion kilometers (9,000,000,000,000 kilometers = 1 ly).

Here is some more measurements (Taken from http://www.astro.princeton.edu/~gk/A403/constants.pdf):

1 pc (Parsec) = 2.06 × 105AU = 3.1 × 1018cm = one parsec, i.e. a distance to a star with a parallax equal to one second of arc. A parallax is an angle at which the radius of earth’s orbit around the sun is seen from a distance of the star. Notice: 2.06 × 105 is the number of seconds of arc in 1 radian.

1 kpc = 103 pc = one kilo-parsec,

1 Mpc = 106 pc = one mega-parsec,

1 Gpc = 109 pc = one giga-parsec,
dH = c/H0 ≈ 1.4 × 1028cm ≈ 4 Gpc = Hubble distance, where H0 ≈ 70 km s−1 Mpc−1 is the Hubble
constant; c = 3 × 1010 cm s−1 is the speed of light. The Hubble distance is approximately the
radius of the observable universe with us at the “center”.

1 R⊙ ≈ 7 × 1010cm = solar radius
Most stars have radii between 10−2R⊙ (white dwarfs) and 103R⊙ (red supergiants); neutron stars