Ultimately, the question of why some planets have moons is still widely debated, but factors such as a planet’s size, gravitational pull, Hill sphere radius and how its solar system formed may ...

Six planets will all be visible at once in the night sky this month, lined up across the sky—but one is set to disappear from view.

On Monday night you may have a chance to witness the moon obscuring the Red Planet at its brightest, as well as a comet’s ...