Distances in space use astronomical units

An astronomical unit (AU) is defined as the average distance between the Earth and the Sun.

1 AU ≈ 150 million km (about 93 million miles)

This unit of measurement is particularly useful for calculating distances within our solar system. It was established by observing the precise alignments between the Sun, Venus, and Earth.

Interstellar distances In light years

A light year (ly) is the distance that light travels in a vacuum in one year.

1 ly ≈ 9.5 trillion kilometres (about 5.9 trillion miles)

Observing distant stars and galaxies allows us to look back in time, as the light we see from these objects has taken millions to billions of years to reach us. This phenomenon helps scientists estimate the size of the observable universe.

From the Sun to Earth - Light takes about 8 minutes

Across the Milky Way Galaxy - Approximately 100,000 light years

Stellar Distances In Parsecs

The concept of parallax is used to measure distances to stars beyond our solar system. Parallax is the apparent movement of closer objects relative to distant ones as the observer's position changes.

A parsec (pc) is the distance at which one astronomical unit subtends an angle of one arc second.

$d = \frac{1}{p}$

Where:

d = distance (Pc)

p = parallax angle in (arc seconds)

1 pc ≈ 3.26 light years, or approximately 31 trillion kilometres (about 19 trillion miles)

The closest star system to the Earth, Alpha Centauri, is just over 1.3 parsecs away, illustrating the vastness of space even within our galactic neighbourhood.