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Unless you add the requirement that they be able to detect us when Earth eclipses the Sun from their perspective.
by ISL 13y ago
Unless 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.