Scale of the universe, illustration. Series of images showing the variation in sizes and distances in the universe. At top is the Earth (12,756 kilometres across). At upper left is the Moon orbiting the Earth at a distance of 384,403 kilometres. At upper right is the Earth orbiting the Sun at a distance of 149,598,000 kilometres (one astronomical unit, AU). At centre left is the Oort Cloud and Kuiper Belt of the solar system, with a radius of 63,240 AU (1 light year). At centre right is the Milky Way galaxy with a diameter of 100,000 light years. At lower left is the Local Group of galaxies with a diameter of 10 million light years. At lower right is the observable universe, with a diameter of 27.4 billion light years.