Alright, I know that "Sol" is used on Mars to count days. But is the sun called: "Sol"? And can you use that term on Earth as well?

The reason for the question is that the term "sol" is used in two ways, but never clarified. Because it also means the sun, and the sun is what time (day/night) is based on on Earth as well as Mars. So why is Sol only used to count time on mars while it is also what time is based on on Earth? And can you use Sol to count time on Earth?

  • 4
    $\begingroup$ Did you try searching? The Wikipedia disambiguation page for 'Sol' is fairly enlightening. $\endgroup$ – Nathan Tuggy Jan 13 '16 at 23:03
  • $\begingroup$ So Out of Luck. (So=a less family friendly word) $\endgroup$ – geoffc Jan 14 '16 at 0:58
  • $\begingroup$ @Nathan Tuggy Doesn't say anything about where it can be used. And it doesn't answer the question in any way. $\endgroup$ – PhoenixFieryn Jan 19 '16 at 22:46
  • $\begingroup$ @DarkLeviathan: It tells you it's used to represent the Martian solar day, but says nothing about Earth. The article linked to then gives an exact duration for the sol, which happens not to match an Earth day; it's therefore reasonable that if there's a single definition (as there usually is), then the sol can only be used on Mars. (The disambiguation page also tells you what the Sun is called.) $\endgroup$ – Nathan Tuggy Jan 19 '16 at 23:58
  • $\begingroup$ @NathanTuggy Yeah, that's the whole reason for asking this question. The pages that I have searched this up at all say that it is used to tell time on mars. However, sol also means the sun. So how can something that is present on all planets be only specific to Mars? Don't we share the same sun as Mars? And don't our time system originate from the sun (day/night)? So that is why I asked this question. That wiki page could not answer the question. $\endgroup$ – PhoenixFieryn Jan 21 '16 at 2:26

A "sol" is only commonly used for a Martian day, and it seems pretty redundant to use this term for Earth, as it is already covered by the concept 'day'. Also, it may induce ambiguity, as people think you are referring to a Martian day.

As for the other planets in the inner solar system, Mercury and Venus, they have a so long day that their orbital period may be a more useful measure of time.

Sol is simply another English word for 'the Sun', and it is also the main word for it in several other languages, including my own (Norwegian).

Some languages use the same word for 'sun' and 'day', including Maori, Hungarian and my second language, Southern Sami.

  • $\begingroup$ I first heard this usage of sol when the Mars rovers Spirit and Opportunity landed and it became necessary for people here to reschedule their lives to martian days. When there is an active, extended robotic mission somewhere else, we'll see if sol is re-used there. $\endgroup$ – uhoh Jan 14 '16 at 10:31
  • 1
    $\begingroup$ @uhoh Where would that be? Venus and Mercury were already mentioned. We already have a word for a Moon-day ("month"). Well maybe on Ceres. On the outer planets and moons, the sun is way dim anyway. $\endgroup$ – Rikki-Tikki-Tavi Jan 26 '16 at 11:02
  • $\begingroup$ mentioned but let's see what's used by those who manage a lander there. And the sun is dim only by earth-based standards. $\endgroup$ – uhoh Jan 27 '16 at 4:16
  • $\begingroup$ along this line I've asked another question here and also here $\endgroup$ – uhoh Jan 27 '16 at 6:47
  • $\begingroup$ Also Hungarian uses the same word 'nap' for both 'sun' and 'day'. $\endgroup$ – bof Jan 27 '16 at 7:46

The term "sol" is short for the word "solar day", which is the amount of time it takes for mars to revolve once around its own axis. A martian sol is approximately 24 hours, 39 minutes, and 35.244 seconds.

The English word is just sun, the Spanish word for sun is sol. the french word is soleil. It would seem sort of redundant to use this term for earth, as it is already used by the concept day.

Also, Earth's days are shorter: they are approximately 23 hours, 56 minutes, and 4 seconds, which is roughly 40 minutes shorter than a day on mars. If you want more information, check out the links. I thought they were helpful :)

  • $\begingroup$ Isn't "the amount of time it takes for mars to revolve once around its own axis" a sidereal day? $\endgroup$ – uhoh Jan 27 '16 at 7:10

Some people haven't actually mentioned that sol is not the name for the sun in English. It is the name for the sun in Latin and you won't hear astronomers say "Oh, look! It's the sol!". However, sol is the name of a Martian day in English, so you will hear astronomers say "The astronauts will be there for approximately 53 sols!".

  • $\begingroup$ That's a good point! I've edited my question here accordingly. Thanks! $\endgroup$ – uhoh Jan 27 '16 at 7:20
  • $\begingroup$ Got it, that clears things up as I thought it was from Latin. $\endgroup$ – PhoenixFieryn Jan 27 '16 at 8:17

First some definitions:

Sol is short for Solar day, that is, the time it takes to get from a point on day one to the same point on day two, based on the Earth's motion relative to the sun (i.e., from the point where the sun is directly overhead one day to the sun in the same position the next day). What is usually used is the average over time, as the length of a solar day can vary (and does, on Earth and Mars, due to axial tilt and elliptical orbits). One mean solar day is 24 hours on Eath, and 24 hours, 39 minutes, 35.2 seconds on Mars.

A Sidereal day, on the other hand, is the time it takes to get from a point on day one to the same point on day two, based on the Earth's motion relative to the stars. It is the time it takes a planet to rotate completely around its axis. It likewise varies. One mean sidereal day on Earth is 23 hours, 56 minutes, 4.1 seconds; on Mars is 24 hours, 37 minutes, 22 seconds.

Sol is the Latin name for the sun (and some other languages derived from Latin), but context should quickly distinguish the two meanings; I can think of no examples (that are not needlessly convoluted) where the two could be mixed up in usage.

The shorter 'Sol' could also be used for the solar days of other planets rather than the full 'Solar day', but is not likely to be, just to avoid confusion. (Mars got dibs on that one!) It might be used with the name of the planet or moon to sufficiently distinguish it. So far the issue hasn't come up, as there is rarely need to reference the length of days on other planets. It only arose with Mars because of the rovers and probes that have been sent there that operate on solar power, making it more convenient for the people who worked with them to operate on the same solar schedule that Mars does. Humans being humans, "Solar day" got shortened to "Sol", and after enough use that became the recognized word for a solar day on Mars (and 'yestersol' as the solar day prior to the current Sol).

  • $\begingroup$ Great summary of the situation! The need to tie ground crew to the solar day of the body on which a lander was operating can be linked to more issues than just solar power, which can also be stored in batteries and used at night. $\endgroup$ – uhoh Jan 27 '16 at 11:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.