Apart from meteorites that land on Earth, or the odd Moon-rock brought back by astronauts, the only way of learning about the Universe is by the electromagnetic radiation that objects in space emit, which we subsequently receive through our various telescopes. Our eyes are sensitive to light that comprises the familiar rainbow of colours – red, orange, yellow, green, blue and violet – but these colours are merely a tiny part of the vast electromagnetic spectrum that extends on either side of the range we can see.