How can a planet's orbit be "counterclockwise"?

[ratatoskK]

From the NY Times article about pictures of extrasolar planets:

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 didn’t realize there was an extrasolar definition of “counterclockwise…” What is it?:rolleyes:

[Bricker]

@ratatoskK

From the NY Times article about pictures of extrasolar planets:I didn’t realize there was an extrasolar definition of “counterclockwise…” What is it?:rolleyes:

The opposite of clockwise.

Duh.

Seriouesly, I think we think of clockwise by thinking first of Earth, and Earth’s north pole being “up.” Once that orientation is established, we can then discuss Earth’s orbit as clockwise or counterclockwise, based on looking “down” at the “clock face.”

[Telemark]

Perhaps related to the magnetic poles of the palnet? Granted, they swap every couple of thousand years, but that would be a way to differentiate the poles and establish “up” and “down”.

[Q.E.D]

Presumably with respect to the galactic North Pole.

[toadspittle]

Perhaps they compare the planet’s orbital direction and rotational direction. Going by our solar system, and using the earth’s north pole as “up”, we can say that the planets all orbit counterclockwise and mostly rotate counterclockwise (Venus rotating clockwise and Uranus rotating “on its side”). Similarly, you could look at an extrasolar planet’s orbital direction, call it “clockwise” no matter what that solar system’s orientation to our own, and then see if the planet rotates in the same direction as its orbit (counterclockwise) or in retrograde (counterclockwise).

[Freddy_the_Pig]

@ratatoskK

I didn’t realize there was an extrasolar definition of “counterclockwise…” What is it?

Don’t make it more complicated than it is. They orbit counterclockwise as seen from Earth.

[Colibri]

@toadspittle

Perhaps they compare the planet’s orbital direction and rotational direction. Going by our solar system, and using the earth’s north pole as “up”, we can say that the planets all orbit counterclockwise and mostly rotate counterclockwise (Venus rotating clockwise and Uranus rotating “on its side”). Similarly, you could look at an extrasolar planet’s orbital direction, call it “clockwise” no matter what that solar system’s orientation to our own, and then see if the planet rotates in the same direction as its orbit (counterclockwise) or in retrograde (counterclockwise).

I’m fairly sure that extrasolar planets cannot be seen in enough detail to determine the direction of their rotation.

After looking at the link, I agree with FTP that the article is referring to the direction of rotation as seen from the perspective of an Earth observer. Look at the video on the site - it shows counterclockwise rotation.

[bonzer]

I suspect the answer’s rather mundane and unprofound: it’s how the orbit looks from Earth.

The Keck Observatory press release about HR8799 is accompanied by this picture with arrows showing the observed motions. Explaining that by saying that they’re all going round the star counterclockwise seems natural enough to me.

[toadspittle]

@Colibri

I’m fairly sure that extrasolar planets cannot be seen in enough detail to determine the direction of their rotation.

After looking at the link, I agree with FTP that the article is referring to the direction of rotation as seen from the perspective of an Earth observer. Look at the video on the site - it shows counterclockwise rotation.

Crap. I misread the OP. I thought it was asking for rotation. And, yes, reading the article, it’s clear that the photos show a counterclockwise motion – as seen from earth – for the planet.