With Mars' thinner atmosphere I'm assuming twilight would not last as long compared to the duration on Earth. Has there been any determination of the length of twilight on Mars at the equator or any other latitude?
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$\begingroup$ Twilight at Earth’s equator is so brief as to be almost non-existent at each equinox, and very modest on the two longest days (the solstices). You only get a “real” summer twilight well away from the tropics, and it lasts the whole “night” around the summer solstice above about the 60th latitude. $\endgroup$Chappo Hasn't Forgotten– Chappo Hasn't Forgotten2019-12-23 21:42:48 +00:00Commented Dec 23, 2019 at 21:42
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1$\begingroup$ @ChappoSaysReinstateMonica I don't understand the "almost non-existent" part of your statement. The website timeanddate.com indicates today, December 23, in Belém, Brazil there will be a total of 2 hours and 31 minutes of morning and evening twilight, and only a few minutes less on September 23. timeanddate.com/sun/brazil/belem. What do you mean by a "real" summer twilight? $\endgroup$Bob516– Bob5162019-12-23 23:29:28 +00:00Commented Dec 23, 2019 at 23:29
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$\begingroup$ Yes, I was a bit loose with my terms, I was thinking how quick civil twilight is at equator vs higher latitudes. On Dec 22 the Sun set at Belém at 18:18, civil twilight ended at 18:41 (23 mins), nautical twilight at 19:07 (26 mins) and astronomical twilight at 19:33 (26 mins). Compare with Ushuaia (54°48′ S): sunset 22:11, civil twilight ends 23:09 (58 mins), and not entering astronomical twilight at all (i.e. twilight lasts all "night"). $\endgroup$Chappo Hasn't Forgotten– Chappo Hasn't Forgotten2019-12-26 22:35:33 +00:00Commented Dec 26, 2019 at 22:35
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2 Answers
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According to https://mars.jpl.nasa.gov/MPF/science/clouds.html twilight lasts up to two hours because of dust high up in the atmosphere scattering the sunlight. Mars Pathfinder is in Ares Vallis, 3°North.
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According to this paper and this paper, twilight cloud is located 40 km above surface at mid-latitude (equivalent to 100 degrees of solar zenith distance), and 80-90 km above surface at equator (equivalent to 110 degrees of solar zenith distance) for Ls (solar longitude) 0-160 degrees.
Thus, twilight at Mars equator occurs 79 minutes (when equinox) until 88 minutes (when solstice)
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$\begingroup$ I don't think those papers support your answer. The atmosphere can reflect and refract sunlight well above where clouds appear. $\endgroup$Greg Miller– Greg Miller2025-09-13 15:35:12 +00:00Commented Sep 13 at 15:35