Distance units in space

Astronomical Unit

An astronomical unit, or AU, is a unit of length that is used to measure distances within the solar system. It is equal to the average distance from the Earth to the Sun, which is about:
150 million kilometers (or 93 million miles)
This unit of measure is commonly used by astronomers and scientists to describe distances within the solar system, since it allows them to easily compare the sizes and distances of different objects.

1 astronomical unit = 149597870700 metres (by definition)
                                    = 149597870.700 kilometres (exactly)
                                    ≈ 92955807.273 miles
                                    ≈ 499.00478384 light-seconds
                                    ≈ 8.3167463973 light-minutes
                                    ≈ 1.58125074098×10−5 light-years
                                    ≈ 4.8481368111×10−6 parsecs

Light-Year

For even larger distances in space, the unit of a "light-year" is being used. A light-year is a unit of distance used to measure large distances in space. It is equal to the distance that light can travel in one year, which is about:
9.46 trillion kilomenters (or 5.88 trillion miles)
This unit is commonly used by astronomers to measure distances between stars and other objects in space. It is a very large distance, so it is often used to describe distances on a cosmic scale. For example, the nearest star to the Earth, Proxima Centauri, is about 4.24 light-years away.

1 light-year = 9460730472580800 metres (exactly)
                     ≈ 9.461 trillion kilometres (5.879 trillion miles)
                     ≈ 63241.077 astronomical units
                     ≈ 0.306601 parsecs

Parsec

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:
3.26 light-years or 206000 astronomical units (au), i.e. 30.9 trillion kilometres (19.2 trillion miles)