We measure the extremely long distances between things in space by light years. A light year is the distance that light travels in one Earth year. Light travels at about 300,000 kilometres per second.

Proxima Centauri b is the closest known exoplanet to our solar system that is thought to be within the habitable zone of its star.

Sedna, a distant dwarf planet three-quarters the size of Pluto, is inching toward the brightest star in our sky — and in 2076 ...