Everything in the solar system moves: planets orbit the Sun, moons orbit planets, and every body spins on its axis. Understanding these motions was one of the first great successes of science, and it is still an active field. The laws of motion Precise orbit calculations led to the discovery of Neptune in 1846, predicted … Read more
A planet’s magnetic field is invisible, but it reveals what is happening deep inside and protects the planet from the solar wind. Astronomers study these fields mostly with spacecraft, and also through auroras and radio waves. Where do planetary magnetic fields come from? Most come from a dynamo: a flowing, electrically conducting fluid inside a … Read more
The Sun is an ordinary star but the center of everything in our solar system. Its gravity holds the planets in orbit, its light and heat make life on Earth possible, and its activity affects space all the way to the edge of the heliosphere. Gravity: the anchor The Sun contains about 99.8 percent of … Read more
A solar flare is a sudden, intense burst of radiation from the Sun’s surface, released when tangled magnetic fields near sunspots snap and reconnect. A large flare can release as much energy as billions of nuclear bombs in a few minutes. Flare classes Flares are ranked by their peak X-ray brightness, measured by satellites. Each … Read more
The difference comes down to one criterion: whether the object has cleared its orbital neighborhood. This definition was adopted by the International Astronomical Union (IAU) in 2006, and it is why Pluto is no longer counted among the planets. The IAU definition of a planet A planet in our solar system is a body that: … Read more
Comets and asteroids are both leftovers from the formation of the solar system about 4.6 billion years ago. The main difference is what they are made of, which determines how they behave near the Sun. Asteroids: rock and metal Comets: dirty snowballs Famous comet: Halley’s Comet returns about every 76 years and is next expected … Read more
