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On earth, it takes a "day" for it to rotate on its axis, and 365 of these days for it to revolve around the sun. On Mercury a "day" that encompasses a rotation represents 59 earth days, while it takes 88 earth days for it to revolve around the sun. This means that a "year" on Mercury is between 1-2 Mercury "days."

What might be the implications of this for Mercury? I am particularly interested in "weather" implications. On earth, a "weather" feature such as a "front" leading to a storm or a hurricane might take several days to unfold, while a climate change might take place over a quarter of a year (a season of 90 days). On the other hand, a "season" on Mercury might be 22 earth days, which is to say less than a 59 (earth) day rotation that represents a Mercury "day."

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    $\begingroup$ 59 days is the sidereal rotation period of Mercury. The Mercury solar day is about 176 days. $\endgroup$
    – notovny
    Oct 27 at 13:20
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Mercury has no atmosphere, so it experiences direct radiative heating and cooling.

The path of the sun in the sky is a slow motion lasting many Earth days and is due as much to the orbit of Mercury (seasonality) as it is due to the rotation (diurnal) The elliptical orbit of Mercury means that the path of the sun can back track

On the side facing the sun temperatures rise to over 400 degrees C. On the side facing away from the sun the temperatures drop to -180 degrees.

Seasonality, i.e. a series of days of hotter temperatures, followed by a series of days with lower temperatures doesn't exist, or rather seasonal variation is appears as just part of the diurnal movement of the sun. There is just "day" when it is hot, and night when it is not.

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  • $\begingroup$ I think OP might be wondering about the weather implications of a planet with Mercury's orbit that also had an atmosphere. $\endgroup$ Oct 27 at 18:28
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    $\begingroup$ Feel free to write your own answer, but the question says nothing of the sort and clearly mentions "Mercury" and not "A planet with Mercury's orbit" $\endgroup$
    – James K
    Oct 27 at 18:44
  • $\begingroup$ I'm very surprised to learn that the path of the sun can backtrack -- Mercury's orbit is surely not that elliptical. Can you provide a reference? (Mercury exhibits retrograde motion when viewed from the earth, but I don't think that's what you mean.) $\endgroup$
    – TonyK
    Oct 27 at 20:15
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    $\begingroup$ see astronomy.stackexchange.com/questions/46937/… and the linked site which states "Mercury's unusual rotation and oval-shaped orbit around the sun means our star seems to quickly rise, set and rise again on some parts of the planet" This is because the orbit of mercury alone would cause the sun to move backwards. When mercury is at perhelion, the sunwill move back and this can cause the double sunrises. $\endgroup$
    – James K
    Oct 27 at 20:19

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