Andrew Conway

The furthest your eye can see

The Andromeda Galaxy Source: Adam Evans CC-BY 2.0

This is the Andromeda galaxy. The nearest galaxy.

The Earth

The Earth seen from Apollo 17 Source: NASA Public Domain

The radius is the distance from the centre to surface

The Moon

The Moon Source: Gregory H. Revera CC-BY SA 3.0

The Moon is the nearest body to the Earth

The Sun

The Sun Source: NASA Public Domain

The Earth orbits the Sun; the nearest star

Proxima Centauri

Proxima Centauri Source: 2MASS Public Domain

The nearest star other than the Sun

Let's use the metre (m)

Let's use the kilometre (km)

1 km = 1000 m

Let's use the Astronomical Unit (AU)

The Astronomical Unit is the distance between the Earth and the Sun.

1 AU = 149,000,000 km

Light units

One light year is the distance travelled by light in one year.

Remember: a light year is a distance, not a time.

Let's use the light units