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Correct on all points. Kepler's already done wonderful work. In order for us/Kepler to detect an exoplanet through the brightness dip as the planet passes betw
by ISL 13y ago
Correct on all points. Kepler's already done wonderful work.
In order for us/Kepler to detect an exoplanet through the brightness dip as the planet passes between its host star and Earth, that planet's orbit (i.e. the ecliptic about the other star) must be in the same plane as Earth.
Consequently, if someone else has discovered Earth with the same method, they must necessarily lie in our orbital plane. If someone knows we're here (and, say, have a lot of water, as might be discernable from spectroscopy) they might be more apt to signal us.
For directed signalling, it's not as important that they be close as it is that they're aware of our planet.
- deletes 13y ago>>that planet's orbit (i.e. the ecliptic about the other star) must be in the same plane as Earth.<< (No, the plane only has to point towards us from any direction, it doesn't have to be on the same plane as earth.) EDIT: I didn't see it from the other perspective. :(
- mnw21cam 13y agoThat's what that means. The Earth has to be on the plane on which their ecliptic sits. However, yes, our ecliptic needn't align with theirs.
- ISL 13y agoUnless you add the requirement that they be able to detect us when Earth eclipses the Sun from their perspective.
- deletes 13y agoOnly now I understand your point. Of course both planet must be able to detect each other, as radio transmissions must be focused to be able to travel the distance and be detected with non-science-fiction telescopes.
- mnw21cam 13y agoIndeed. For two-way detection, the two ecliptics must be in the same plane. Or more accurately, the two ecliptics must be close enough to a common plane, where the common plane passes through both planets and "close enough" means within half a degree on Earth's side.