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Message: <blockquote data-quote="Aexalon" data-source="post: 5411918" data-attributes="member: 16283">I just did some calculations for a star like <a href="http://en.wikipedia.org/wiki/Gliese_581" target="_blank">Gliese 581</a>, considering 2 planets: a terrestrial one at the same solar intensity as Earth is (at 17 million kilometers, sidereal year = sidereal day = 24.5 earth days), and a <a href="http://en.wikipedia.org/wiki/Hot_Jupiter#Puffy_planets" target="_blank">puffy</a> gas giant like <a href="http://en.wikipedia.org/wiki/COROT-1b" target="_blank">COROT-1b</a> with a sidereal year of 24h (~ 2 million kilometers; I know, should have aimed for a synodic year of 24h, but for now, this is close enough), and behold, the hot jupiter is (and looks) half the size (0.793 degrees) of the star (1.35 degrees)! Did not expect that. The Sun and Moon both measure about 0.5 degrees, for reference.Further back-of-napkin calculations would indicate that the antumbra of the hot jupiter at the distance of the habitable planet would be 1.3 million km wide (in this zone, the gas giant would at some point appear wholly on the disk of the star), and the penumbra a staggering 4.7 million km wide (in this zone, the gas giant would obscure at least part of the star)! That would definately result in quite noticeable transits, presuming the 2 planets' orbit planes don't differ by more than 15.45 degrees (penumbra) or 4.37 degrees (antumbra) — quite reasonable; e.g. Earth's and Jupiter's orbital planes are inclined at only 1.3 degrees to eachother.So, geometrically, it's possible. Whether such a large planet that close to its star in combination with a terrestial planet in the star's habitable zone is physically possible (and/or likely), I'm not 100% sure. But it probably is.And I had this whole rant prepared about how hard it is to see Mercury with the naked eye, and how this hot jupiter'd be 29 times closer to it's star... Good thing I tried the math first <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f600.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":D" title="Big grin    :D"  data-smilie="8"data-shortname=":D" /></blockquote>

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