Israeli astronaut Ilan Ramon had a question before going into space: How would he mark Sabbath, the Jewish day of rest, from orbit? Sabbath begins Friday at sunset and ends Saturday after sunset. But ...

For years, astronomers have predicted a dramatic fate for our galaxy: a head-on collision with Andromeda, our nearest large galactic neighbor. This merger—expected in about 5 billion years—has become ...

“Megaconstellations” of vast numbers of satellites could threaten space-based astronomy, scientists have warned.