What Planet Has The Shortest Year?
The planet in our solar system with the shortest year is Mercury. Mercury orbits the sun once every 88 earth days, thus its year is 88 days long. This is because mercury is also closest to the sun. The greater the orbital distance from the sun, the longer the year on that planet.
I watched a program last night on the History Channel called “The Universe.” On this program they talked about this planet orbiting another star. This planet was so close to the central star that it’s orbit only took three and a half days to complete. So, A year on that hot ball of gas planet would only be three and a half days. This planet is named TrES-4 and more information on it can be found here.
The planet in our solar system with the longest year is Pluto. Pluto takes 248 and a half earth years to orbit the sun. Even though Pluto has been demoted to dwarf planet status, it’s still a planet of sorts, so it’s orbit counts as the longest year.
A planet’s orbital period only depends on its distance from the sun and the ellipticity of it’s orbit. The greater the distance, the longer the orbital period, or year. If the sun were more massive and the planets were at the same distance, the force of gravity would be greater and the planets orbits would have shorter periods.
It was possible to observe the orbits of the planets by comparing their positions in the sky with the background of stars. The orbits of the planets were known long before they were explained. Johannes Kepler derived an empirical formula for the orbits of the planets based on his observations. He observed that a planet will sweep out an equal area with it’s orbit in an equal period of time. This empirical law led Sir Isaac Newton to derive his laws of planetary motion based on the law of universal gravitation he developed.
Because it is so close to the sun, it is hard to observe the planet Mercury. Mercury can be seen sometimes just after sunset or before sunrise. Because it moves so fast in the sky, Mercury was named for the swift messenger of the Roman gods, Mercury.