What is the difference between a moon and a planet? Trick question! According to scientific definitions, there often isn’t much of a difference at all. That might seem counterintuitive, but it’s true.

Binoculars or small telescopes easily show double stars and star clusters. Several planets are visible this week, some with moons or other celestial neighbors. The changing position of planets and the ...

A celestial event called a conjunction featured the moon, Venus, and the star Regulus on Sept. 19. The trio will still be shining on Sept. 20, but Venus and Regulus will be further from the moon. The ...

Space has a knack for bending our sense of scale. The Moon feels close enough to touch—after all, we see its craters with nothing but our eyes. Yet, that 238,855-mile gap between Earth and its lunar ...