A total solar eclipse will be visible from Texas to Maine on Monday. This cosmic event occurs when the Earth, sun, and moon align perfectly. One diagram shows how a total solar eclipse works, and why ...

To receive the same amount of starlight as Mars receives from our sun, a planet orbiting an M-type red dwarf would have to be positioned much closer to its star than Mercury is to the sun. Disclaimer: ...

The solar system once had five giant gaseous planets rather than the four it has today. That’s the conclusion from a computer simulation of the solar system’s evolution, which suggests the fifth giant ...

This story is a collaboration with Biography.com. Few things seem as immutable than the Sun—after all, it’s been fusing hydrogen for five billion years, and it’ll keep on ticking for about five ...