Friday, November 14, 2008

Far off planets that revolve ... anti-clockwise?

Perhaps the answer is that I am startlingly ignorant but I was struck by this sentence when I was reading in the NYT about the discovery of far-off planets (or rather the first photographic evidence) beyond the solar system:
The three planets orbiting HR 8799 are roughly 10, 9 and 6 times the mass of Jupiter, and orbit their star in periods of 450, 180 and 100 years respectively, all counterclockwise.
I am sorry but how exactly does one determine whether a planet revolves clockwise or counterclockwise? How does one look? From the top? The bottom? How are directions determined when we are dealing with things on the planetary scale? Is this just a typo from the reporter?

2 comments:

Preetha said...

You dont need observe it from Earth, but I think a satellite in orbit (taking a longer path) could capture that information. By capturing IR images over a period of time perhaps...maybe I am just rambling here:)

Sugavan said...

Probably by keeping one relative point to all things in the Universe, say, the Earth, is it anti-clockwise w.r.t Earth? The planet might take a bagillion years to come to the other side of earth by which time it'll be clockwise, but that wouldn't matter I guess...