Understanding our Solar System -Galileo Galilei

Galileo Galilei 1564 – 1642

Galileo was the first astronomer to use a telescope to make observations that supported the heliocentric model of the Solar System as proposed by Copernicus.

Galileo observed Jupiter's moons orbiting around the planet. This observation negated the geocentric model put forward by Ptolemy. The Earth was not the only centre of motion.

Supporters of Ptolemy's model argued that the Moon would be left behind if Earth was to move through space. Galileo’s observations showed that moons could orbit a moving planet as was happening with Jupiter's moons.

View the NASA video on the right.

a) What were the stars Galileo observed orbiting around Jupiter?

b) Why did this observation revolutionise astronomy?

c) What did NASA's Galileo mission discover on the moons of Jupiter?

When viewed without a telescope, Venus appears as a bright dot in the sky. When Galileo used a telescope, however, he was able to observe the phases of Venus. There was no way a geocentric model could account for these phases and could only occur if Venus had an orbit around the Sun.