The Parallax Effect

The Greeks thought that the earth was at the center of the solar system because they figured if their earth was moving around the sun they would see this parallax effect. They didn't realize the stars are much much further away than they actually were and that's the thing about parallax it only works for pretty close by stars even still the wiggle is pretty subtle we didn't detect it until like the 19th century. There's special kind of stars called cephids cephids are stars that do something really cool to vary in their brightness.