Astronomical unit

The Astronimical unit (abbr. au or AU) is a unit of length used in astronomy.

1 AU is roughly the average distance from Earth to Sun or ~150 million km.

Definition[]

On August 31, 2012, in "Resolution B2", the 28^th General Assembly of International Astronomical Union in Beijing re-defined the astronomical unit to be a conventional unit of length equal to exactly 149,597,870,700 metres.^[1]^[2]

The unit Parsec (pc) is based on the astronomical unit:

1 Parsec	= 360·60·60 / 2π astronomical units
	≈ 206 264.8 AU
	≈ 3.085 677 581 491 37 × 10¹⁶ meters
	≈ 30 856 775 814 913.7 kilometers
	~ 3.26 light-years

In other units[]

1 AU	= 149 597 870 700 meters (exactly)
	= 149 597 870.7 kilometers
	≈ 92 955 807 miles
	≈ 499.004 783 84 light-seconds
	≈ 15.812 507 millionths (15.812 507 × 10⁻⁶) of a light-year
	≈ 4.848 136 8 millionths (4.848 136 8 × 10⁻⁶) of a parsec
	= 2π / (360·60·60) Parsec

Distances in Sol system[]

Some distances of planets and asteroids in Sol system (approximate):

Body	average from Sun		closest from Earth		farthest from Earth
Body	AU	Mio km	AU	Mio km	AU	Mio km
Mercury	0.387	58	0.516	77.3	1.483	222
Venus	0.723	108	0.267	40	1.743	261
Earth	1	150
Mars	1.52	228	0.37	55	2.68	401
Eros	1.13 - 1.76	169 - 267	0.15	23	2.77	414
Ceres	2.77	414	1.6	240	2.75	413
Jupiter	5.2	778	3.93	588	6.59	968
Saturn	9.58	1 433	8.02	1 200	11.36	1 700
Uranus	19.21	2 875	17.17	2 570	21.04	3 150
The Ring	21.2	3 173	20.2	3 024	22.2	3 323
Neptune	30.11	4 500	28.72	4 300	31.4	4 700