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Astronomy

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  • $\begingroup$ Great answer. But it assumes that the part of the planet always facing the star receives extreme amount of energy and ends up with the very high surface temperatures. Why such assumption? Isn't it possible to have an Earth-like scenario only without the rotation? A planet that would have everlasting day on one side and everlasting night on the other side, but with medium temperatures similar to Earth's medium day and night temperatures? $\endgroup$
    – trejder
    Commented Oct 5, 2023 at 13:34
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    $\begingroup$ But surely that just moves the goldilocks zone. Surely there is a radius from the star at which a day side tidally locked planet would be a comfortable temperature. Its just further from the star than for a normal planet $\endgroup$
    – Richard Tingle
    Commented Oct 5, 2023 at 22:22
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    $\begingroup$ You need to demonstrate, or argue, that in order to be tidally locked, the surface temperature on the illuminated side must be too hot, for any kind of central object. I don't think that is the case. $\endgroup$
    – ProfRob
    Commented Oct 6, 2023 at 6:07
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    $\begingroup$ @RichardTingle if only the day side were a comfortable temperature, then all water that evaporates there would eventually diffuse over to the night side where it is so cold that the vapour resublimates to form a giant ice sheet. The process ultimately dries out the day side, even if the temperatures are perfectly harmless there. This can only be avoided if the atmosphere is so thick that it can equilibrate the temperature difference between day- and night side. $\endgroup$
    – leftaroundabout
    Commented Oct 6, 2023 at 15:40
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    $\begingroup$ @trejder "Earth's medium day and night temperatures" are only what they are because of the cycle. Night would lose its stored heat if the heat weren't replenished each day. Day would gain tons of heat if it didn't have a chance to lose the accumulated heat overnight. To give an idea of this effect, consider how much hotter noon is than dawn. Today where I live there was a difference of about 5°F over 5 hours, and I'm sure we've all seen more dramatic rises than that. The temperature began to fall mid-afternoon as the sun declined. But what if the sun never set and only kept pouring energy in? $\endgroup$
    – Luke Sawczak
    Commented Oct 6, 2023 at 20:48