Phebe Posted April 20, 2009 Report Posted April 20, 2009 to me what a transiting planet is? I'm reading this article about how we can't measure the size of some planets because they do not cross the disc of their home star. Really what I don't understand is the term "cross the disc of their home star", does that mean they don't orbit their star. And if so how can they then be planets? I thought that was a criterion. I am probably misunderstanding the term and will be in agony until it is explained to me. Quote
Pyrotex Posted April 20, 2009 Report Posted April 20, 2009 Aha! Here I am! To save the day! Hello, Phebe, and welcome to Hypography.The term "transit" refers to a planet crossing in front of the disk of its sun.Mercury and Venus (in our solar system) occassionally are seen in silhouette, crossing the disk of our Sun. This does not happen on every orbit, because the plane of Mercury's orbit and the plane of Venus' orbit are tilted just slightly from the plane of Earth's orbit. For distant suns and their planets, the term "transit" means much the same, though we do not have telescopes even remotely powerful enough to show a moving black dot against the disk of those distant suns. However, we can detect a transit by measuring the light output of the star to great precision. If a planet does transit the star, then the light output might decrease by a fraction of a percent -- and we can measure that! The planets in question are always in orbit about their home star. A transit occurs when they happen to be at a point in their normal orbit that just happens to be directly between its star and our telescopes. That means the plane of that planet's orbit must be "edge on" to us. If not, then we will never see a transit of that particular planet. Assuming planets between the sizes of Earth and Jupiter; and assuming those planets have orbits between, say, 1/10 of Mercury's orbit out to Saturn's orbit; and assuming that the star has a size between half our Sun and twice our Sun -- the math indicates that there is about a 2% chance that any given star out there will have a detectable planet that will transit. Is that better? Quote
Phebe Posted April 20, 2009 Author Report Posted April 20, 2009 Jesus, you guys are life-savers. Thank you so much. I understand perfectly now. Don't you just love hypography? Quote
Pyrotex Posted April 20, 2009 Report Posted April 20, 2009 Jesus, you guys are life-savers. Thank you so much. I understand perfectly now. Don't you just love hypography?Yes indeedly I doodly! :) :) :) :) Quote
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