View Full Version : Searching for planets by viewing star wobble

2003-Sep-29, 03:31 PM
I have always wondered how Earth's own orbit affects our observation of stars as they wobble due to planets orbiting the star. Are there formulas that the astronomers apply to account for our own orbit around the sun? Does our own orbit affect our viewing of the wobble (due to the change in perspective) or is it a non-issue due to the great distances involved?

2003-Sep-29, 10:34 PM
Good question Richie. Welcome to the forum! To be honest I'm not entirely sure. It's a highly exact science so I guess they'd have to factor the Earth's orbit (i.e. our own "wobble") into the calculation.

For short observations, I'm pretty sure parallex error is minimal at such great distances, and they not even need to worry about it (don't quote me on that). The same can be said about inferometry. If the two telescopes were an earth diameter apart, they might not take a very good picture of the moon, but they could still view other objects, even the planets of our own solar system which are relatively close.

That being said, If you're viewing the wobble of a planet over 8 years, and not 3 days, it obviously affects where they point the telescope from night to night, and stellar wobble might be hard to detect unless it was factored into your calculations.

Another question might arise...what if the particular star under observation isn't viewable for part of the year as we are on the opposite side of the sun? Can they still measure minute changes in the spectrum shift of a star when it is close to the sun in the sky?


2003-Sep-30, 06:40 PM
Very good question. I've wondered that myself. Especially considering the size diff between our own star, the Sun, and the first four planets. Then our gas giants are so far away, one would wonder how they could cause a wobble. But the planet finders claim small movements are detectable. It's math well beyond what I know.

2003-Oct-02, 07:00 PM
Thanks for the reply. (sorry I was delayed, I am knee deep in month end processing at work right now). You raise good questions. I only wish I had a better understanding of the subject other than just a hobbiest's interest.

This from a friend I am I/Ming right now:

Think of it this way - if you can opbserve two stars that you know are at rougly the same distance from earth and one exhibits a positional difference that is irrespective of parallzx experienced on the other, then the positional difference can be "subtracted out" of teh parallax. Also - we know pretty precisely how big our orbit is, and it is a VERY simple thing to calculate parallax expected from that.

ok. I think i get you.

Besides - I would not expect all planets to orbit in the same plane as we do - which means parallax will be experienced in one direction (let's say left-right) and planatary rotation in another (let's say, up-down)!

Thing is - we know precisely how WE move - any movement we can see in stars that is not accounted for by our movement - must be caused by something else!