venus, mercury axis rotation? Bug? Or reality?

steve.wray · Post #1by **steve.wray** » 10.07.2002, 03:17

I just noticed that while Venus appears not to rotate on its axis in celestia, Mercury does.

I thought that Mercury was (tidally?) locked to the Sun and always had the same face toward it? (maybe it rotates very slowly in reality?)

Venus, on the other hand, while the cloud cover might not move a lot, I'm certain that it *does* rotate on its axis...
Yet in celestia I can clearly see features on the texture, and I can clearly see that it doesn't rotate at all... even at timex1000000

Are these bugs in celestia, or are these accurate?

Matt McIrvin · Post #2by **Matt McIrvin** » 12.07.2002, 06:14

steve.wray wrote:I thought that Mercury was (tidally?) locked to the Sun and always had the same face toward it? (maybe it rotates very slowly in reality?)

This was once believed by astronomers but has been known to be false since the sixties. Actually Mercury's sidereal rotation period is tidally synchronized to exactly 2/3 of its year (what this means with regard to its "day" is left as an exercise for the reader).

Venus has an even slower sidereal rotation period that is longer than its year. This doesn't correspond to the cloud cover patterns, though, which I think blow around the planet much faster than that in reality. But in my copy of Celestia, they seem to be rotating at the sidereal rotation rate. Are you sure you aren't in sync orbit?

Post #3by **chris** » 12.07.2002, 21:46

Thanks for point that oversight out . . . I need to modify Venus so that its clouds move rapidly over a very slowly rotating service. Oops.

--Chris

steve.wray · Post #4by **steve.wray** » 12.07.2002, 22:02

and thanks for bringing reality to my attention!
I had *no* idea that venus rotated so slowly!

In the tests I ran, I made certain that I was viewing earth, mercury and venus with exactly the same settings; earth was spinning like a top, mercury was slowly turning and venus didnt *seem* to turn at all.

stevenabors · Post #5by **stevenabors** » 31.07.2002, 05:08

Mercury's rotation is 59 earth days, year is 88 earth days, exactly 2/3s of its year

Venus' rotation is 243 earth days and is retrograde, (backwards, counter clockwise as seen from above)

stevenabors · Post #6by **stevenabors** » 31.07.2002, 05:11

stevenabors wrote:Mercury's rotation is 59 earth days, year is 88 earth days, exactly 2/3s of its year

Venus' rotation is 243 earth days and is retrograde, (backwards, counter clockwise as seen from above)

Clockwise I mean