As with the
Moon around the Earth ,
the planets in our Solar System are held in motion around the Sun
by gravity.
Thousands of years ago the Greeks thought that there were only
five planets with the Earth at the centre of it all.
Then in 1543,
Nicholaus Copernicus came up with the bright idea that it was in fact
the Sun that was at the heart of the Solar System and that the planets
revolve around it.
Another scientist
Johannes Kepler (1571-1630), using observations made by
Tycho Brahe (1546-1601)
spent his whole life working out
how the planets move across the night's sky.
He concluded that the planets actually follow a path that draws out
a shape called an ellipse.
Image Copyright: Calvin J. Hamilton
