What Is the Sidereal Period of Planets?


My name's Eric Loberg, the director of the Taylor Planetarium here at the Museum of the Rockies. I was going to discuss Sidereal period of the planets. What a sidereal period is, is the time that it takes a planet to go all the way around the sun. This is revolution, around the sun in an orbit, in respect to the stars. So, if you were standing on the planet and you could see a star in orion. How long would it take you get back and have that same star in the same portion in the sky? That's just the orbit of the year of these planets. So, the closer you are to the sun, the faster that's orbit's going to be. Mercury is 88 days, Venus is 225 Earth days, Earth is that 365 and a quarter days. Mars is 687. Here it becomes a little easier to talk about years, almost two Earth years, Jupiter's almost 12 Earth years, Saturn's 30 Earth years, Uranus is 84 and Neptune is a 166. The farther from the sun these planets, the longer it takes to go all the way around the sun one time and see those stars. We can also talk about a sidereal period on its rotational basis. when it goes around and sees the same stars from one day to the next. How does it take a planet to move and see the same stars in hours. And this will be a little bit different. The bigger the planet, the faster that that goes on, generally. And so, we have in hours, the rotational period now. Mercury is 1400 hours, Venus with negative almost 6000 and that's because it's actually backwards in comparison to the rest of the planets. Earth is 23 hours and 56 minutes, not quite 24 hours. Mars is 24 hours point six, almost an Earth day, just a little bit more. Jupiter, nine point nine two, Saturn, 10 point six six, Uranus, 17, Neptune 16. Those big planets, all have a lot of matter, they squish down, they started rotating very fast. So, their hourly day is quite a bit shorter then the large planets. So that's the sidereal period of the planets, as they rotate around in a day. We also looked at the revolutionary period in the sidereal fashion. My name's Eric Loberg, Museum of the Rockies, Taylor Planetarium director.

J. Eric Loberg is the manager, lecturer, and program planner at the Taylor Planetarium at the World, a renowned museum of the Rockies in Bozeman, Montana.