Keep your eye on the ball” is a motto for many athletes—and for astronomers trying to find Earth-threatening space rocks ...

"In about 1604, Johannes Kepler fitted an ellipse model of Mars' orbit to observations of Mars," Bloomer told Space.com. "He came up with the first law of planetary motion that states that planets ...

If this were true, then each planet's orbit should take the form of Kepler's ellipse, a shape like a football, though somewhat more rounded. Halley recalled that Hooke immediately "affirmed that ...