Why didn't someone prove that the heliocentric model was correct sooner?

Answer 1

You'd think they would have done, it took all of 1500 years. The reason is that the old Ptolemaic model predicted the positions of the Sun, Moon and planets in the sky quite accurately so that there was little reason to suspect it might not be quite right.

It was only in the late 16th century that the model became suspect, after Tycho Brahe had invented new and more accurate ways of measuring the positions of stars and planets. His measurements were used by Johannes Kepler to produce the laws of planetary motion, in which the planets' orbits were described as ellipses, and this produced better agreement between predictions and measurements.

Kepler's model had to have the Sun assumed at the centre, but at that stage it was only recognised as a convenient assumption. But in the next 100 years, after the time of Tycho, Kepler and Galileo, further basic scientific discoveries of gravity and the laws of motion were made that fitted the heliocentric theory and made it more and more acceptable.

Finally, in the 19th century, observations became so sophisticated that the parallax of nearby stars could be measured, which produced the final piece of the scientific jigsaw and led to the general acceptance of heliocentrism. The first measurement of parallax was done on the nearby star 61 Cygni by the German astronomer Bessel. Parallax is a very slight regular shift of a star's position against the background of distant stars, caused by the Earth's movement round the Sun. That was the knockout punch that finally decided the debate.