SOLAR SYSTEM

Detailed explanation-1: -A planet’s orbital speed changes, depending on how far it is from the Sun. The closer a planet is to the Sun, the stronger the Sun’s gravitational pull on it, and the faster the planet moves. The farther it is from the Sun, the weaker the Sun’s gravitational pull, and the slower it moves in its orbit.

Detailed explanation-2: -On July 4, 2011, when the Earth was farthest from the Sun (aphelion, 152.1 million kilometers) it was traveling at 29.3 km/s.

Detailed explanation-3: -The closer a planet is to the Sun, the less time it takes for it to go around the Sun. It takes less time because the length of the orbit is shorter (a smaller orbit), but it also moves faster in its orbit. Thanks to gravity, it has to move faster in its orbit to stay in orbit!

Detailed explanation-4: -They move pretty quickly! The planets all orbit at different speeds. The closer a planet is to the Sun, the faster the planet orbits. Mercury is the fastest planet, moving at 47.87 km/s while Neptune orbits at 5.43 km/s.

Detailed explanation-5: -For the outer planets they have further to go and a slower speed so their orbital periods are much longer than that of the earth. e.g. saturn is 9.5x further from the sun than the earth is, but its orbital period is 29.5x that of the earth. Planets shine in visible light only by reflected sunlight.