Deep Space

Heather Couper presents a narrative history of astronomy.

In 1845 the third Earl of Rosse completed the biggest telescope in the world at his castle in the centre of Ireland. In spite of cloudy skies, this leviathan enabled him to see spectacular detail in the sky, including a spiral structure in certain fuzzy patches known as nebulae. Some of these seemed so big that astronomers thought they must be rotating clouds of gas out of which planetary systems are born.

Henrietta Swan Leavitt refuted this, studying variable stars and realising that a certain type of star varied at a rate that was linked to its brightness. These so-called Cepheid variables could be used to estimate the vast distances of space.

In 1919, the young Edwin Hubble used a new telescope in California to search for Leavitt's Cepheids in spiral nebulae. He discovered, to his astonishment, that the nearest, the Andromeda nebula, lay well outside our own galaxy and constituted an island universe in its own right.

Readers are Timothy West, Robin Sebastian, Julian Rhind-Tutt and John Palmer.