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Old 4th November 2019, 02:03 PM   #14
RecoveringYuppy
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Join Date: Nov 2006
Posts: 10,702
Originally Posted by rjh01 View Post
Would have thought that planets going around other suns would rarely go between their sun and us for the same reason that Mercury and Venus rarely go between the sun and us.
I'll rephrase other peoples correct explanations in order to add another point.

We don't see transits frequently because the orbits of Mercury, Venus, and Earth are all tilted. For the situation in this solar system, the tilt means that most of the times when Venus or Mercury pass "in front" of the Sun, they will pass either above it or below it. The only times when we'll see a transit is when the Earth is near the one line of intersection that Earth's orbit shares with the other planet (the "node" that was mentioned earlier).

For distant star systems that distance means that the tilt of our orbit doesn't mean much at all and neither does our orbit*. Earth is essentially a stationary point. If Earth is on a line that intersects both that distant star and the planet orbiting it then we are in that planets orbital plane and will be every orbit it makes.

However, "the same reason" that you referred to may also be in play in that distant star system. The planetary orbits in that system may also have different tilts. What that means to us though is that those planets will never transit the star from our point of view. You probably already know that the transit method requires the distant star system be view "edge on" and only works for a small percentage of systems that are properly oriented towards us. However, it also means that even in a system that has some well oriented planetary orbits, not all planets in that system will necessarily have similar opportune orbits.

* There are some edge cases where those factors matter.

Last edited by RecoveringYuppy; 4th November 2019 at 02:05 PM.
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