Australian Sky & Telescope

Seventy-nine & counting: Finding Jupiter’s moons

IN THE HIERARCHY OF THE SKY, Jupiter has always enjoyed a front-row seat. With its prominence exceeded only by the Moon, Venus and occasionally Mars, Jupiter is usually the third brightest object in the night sky. It’s little wonder that the Romans named it the king of the gods.

On January 7, 1610, Jupiter’s eminence surged when Galileo Galilei aimed his newly built telescope at it and observed what at first appeared to be three nearby stars hugging the regal planet. Then, on January 11, he saw four. Documenting the first planetary moons other than our own, Galileo vaulted to lasting fame. The discovery of these four worlds was one of the most momentous turning points in astronomical history, challenging the established belief that Earth was the centre of creation around which all heavenly bodies revolved. Suddenly there was another system — one in which our planet didn’t occupy the exclusive focus of the firmament.

In March 1610, Galileo published his findings in a pamphlet, (), an account of his observations of Jupiter’s satellites, the mountains and craters of

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