The International Astronomical Union defines a planet as a celestial body that orbits the sun, is massive enough that gravity has forced it into a spherical shape, and has cleared away other objects ...
In this video segment adapted from NOVA scienceNOW, learn about the debate over the definition of a planet. Historically, there has been no scientific definition for a planet, leaving astronomers with ...
Some results have been hidden because they may be inaccessible to you
Show inaccessible results