The Sun, an unremarkable star, holds in orbit a system of planets. If most Sun-like stars have planets, then there should be billions of planets in our Milky Way Galaxy. Numerous other planetary systems have already been detected, many with configurations quite different than that of our solar system.
In our solar system, planets are the major bodies orbiting the Sun.
Until the end of the 20th century, ours was the only planetary system known. We now know of more planets outside our solar system than within it.
Many forces shape the solid surfaces of planets and moons.
Visible sunlight heats a planet’s surface, which re-radiates the energy as infrared light. Certain atmospheric gases absorb and trap much of this infrared energy, raising the temperature at the surface.
Volcanoes provide an efficient way for solid planets and moons to shed their internal heat.
Great atmospheric storms occur on all the gas giants.
All of the gas giant planets have rings.
The Moon orbits Earth. Earth orbits the Sun. The Sun orbits the center of the Milky Way Galaxy. Gravity governs all of these motions, holding moons, planets, and stars in their orbits.
The ancients believed that Earth was the center of the universe.
The Sun and the planets formed together, 4.6 billion years ago, from a cloud of gas and dust called the solar nebula.