Learn how astronomers measure planet mass using radial velocity, transits, timing, and imaging, plus the limits that shape every estimate.

Learn how astronomers name planets, moons, asteroids, comets, and dwarf planets using International Astronomical Union standards.

Learn how dwarf planets differ from planets, asteroids, and moons, with clear examples from Pluto, Ceres, Eris, Haumea, and Makemake.

Learn which planet is closest to the Sun, why Mercury holds that title, and how its extreme orbit shapes conditions there.

Learn how gravity, pressure, composition, and rotation determine why planets become round and what keeps some worlds from being perfectly spherical.

Learn how solar activity drives space weather, from flares and CMEs to geomagnetic storms, radio blackouts, and auroras.

Learn what the asteroid belt is, where it sits in the Solar System, what it’s made of, and why it matters to planetary science.

Learn how comets form glowing tails, why they point away from the Sun, and what solar radiation reveals about these icy bodies.