Algol, a variable star in the constellation Perseus. (A variable star is one that changes in brightness.) Algol, which was observed by the ancient Greeks and named by the Arabs, is now known to be a complex system of at least four stars revolving around one another. A pair of the stars forms an eclipsing binarytwo stars that pass in front of each other in turn, causing a periodic (cyclical) dimming of their combined light. Algol dims regularly every 21 days and 21 hours.
Galaxies got their start nearly 14 billion years ago, with one unimaginably hot, dense and tiny pinpoint. How did we arrive at the universe's sprawling state of galactic affairs today?
It's tough to wrap your mind around a time when the Earth wasn't here. So how do Earth and the rest of the planets out there get their start in the universe?