The following units of length are often used to measure large distances (for example, in astronomy and astronautics): the astronomical unit, the light year and the parsec.
The astronomical unit of length (AU) is the mean distance between the Earth and the Sun:
1 AU = 1.496·1011 m.
The light year (ly) is the distance travelled by a ray of light in one year:
1 ly = 9.460·1015 m.
The parsec (pc) is the distance from which the radius of the Earth’s orbit is seen at an angle equal to one second:
1 pc = 3.086 ·1016 m.
The table gives the symbols of these units, their numerical values and the relations between them.
The time in which light travels a distance of 1 AU is 499 s.
The mean distance from the Moon to the Earth is 0.00257 AU.
The smallest distance from Venus to the Earth is 0.27 AU.
The greatest distance from Venus to the Earth is 1.73 AU.
The distance from the Earth to the Milky Way is 8000 pc (8 kpc)
The radius of the observable part of the Universe is 1040 Mpc.
The astronomical unit of length (AU) is the mean distance between the Earth and the Sun:
1 AU = 1.496·1011 m.
The light year (ly) is the distance travelled by a ray of light in one year:
1 ly = 9.460·1015 m.
The parsec (pc) is the distance from which the radius of the Earth’s orbit is seen at an angle equal to one second:
1 pc = 3.086 ·1016 m.
The table gives the symbols of these units, their numerical values and the relations between them.
| Unit | AU | ly | pc | km |
|---|---|---|---|---|
| 1 AU | 1 | 1.57·10-5 | 4.848·10-6 | 1.496·108 |
| 1 ly | 6.324·104 | 1 | 0.3066 | 9.460·1012 |
| 1 pc | 206 265 | 3.262 | 1 | 3.086·1013 |
| 1 km | 6.684·10-9 | 1.057·10-13 | 3.241·10-14 | 1 |
The mean distance from the Moon to the Earth is 0.00257 AU.
The smallest distance from Venus to the Earth is 0.27 AU.
The greatest distance from Venus to the Earth is 1.73 AU.
The distance from the Earth to the Milky Way is 8000 pc (8 kpc)
The radius of the observable part of the Universe is 1040 Mpc.