Mars Jewish Calendar

The Martian Jewish Calendar  – Draft Discussion


As talk about future missions and colonization of Mars grow, though currently still far-fetched and barring some Halachic opinions against encouraging Jews to undertake what would initially be highly dangerous journeys, I thought it would be an interesting exercise to imagine the need for a suitable halachic framework for keeping halachic time on a different planet.

First some facts about Mars:

  • Its average day lasts the equivalent of 24 hours, 39 minutes and 35.244 seconds (known as a sol).
  • The average Martian year is the equivalent of 687 days.

Now for a Jew wishing to keep halachic times there are multiple complications and various contradictory opinions regarding travelers in places where it is difficult or impossible to determine or relate to what we would consider “normal” earthly time. See the multiple responsa about travelling to the North Pole, orbiting the Earth or even crossing the International Dateline.

Examining cases of Jews in the North or South Pole where one cycle of day and night takes 365 Earth days, or in orbit, where they are experiencing the daily cycle every 90 minutes, gives us a wide variety of Rabbinic opinions. Some opinions explain that the person is outside of conventional time and therefore is exempt from time-dependant prohibitions. However, the practical consensus that seems to be used by polar explorers as well as astronauts is to base their schedules on either the closest inhabited city or in the case of astronauts on their control base. So for example, Jewish NASA astronauts have synchronized their halachic time with that of Houston, Texas, the location of the Johnson Control Center, which manages the operations on the Space Shuttles and the International Space Station. So independent of the fact that astronauts in orbit will experience sunrise and sunset every 90 minutes, their daily schedule is actually more closely governed by the sunrise and sunset in Houston.

The challenge on Mars will be somewhat different. On one hand it has its proper sunrise and sunset which is fairly close to what one might experience on earth and will likely be vital to the operations of any Martian operation. On the other hand, if one were to keep “days” of Martian length, in a relatively short time, there would be a growing discrepancy between the Earthly calendar and the Martian one.

So on average, every 36 days, Mars would be one day “behind” Earth. So for example if Earth and Mars were to start counting Sefirat Haomer on the same day, after 37 days of counting on Earth, Mars would only be up to day 36.

While one might argue that Mars should have its own calendar, independent of Earth, our sense is that there would be significant value in the calendars being connected as much as possible, especially regarding observance of the Holidays and Sabbath. See especially Tractate Rosh Hashana, Chapter 1, Mishnas 3 and 4.


עַל שִׁשָּׁה חֳדָשִׁים הַשְּׁלוּחִין יוֹצְאִין, עַל נִיסָן מִפְּנֵי הַפֶּסַח, עַל אָב מִפְּנֵי הַתַּעֲנִית, עַל אֱלוּל מִפְּנֵי רֹאשׁ הַשָּׁנָה, עַל תִּשְׁרֵי מִפְּנֵי תַקָּנַת הַמּוֹעֲדוֹת, עַל כִּסְלֵו מִפְּנֵי חֲנֻכָּה, וְעַל אֲדָר מִפְּנֵי הַפּוּרִים. וּכְשֶׁהָיָה בֵית הַמִּקְדָּשׁ קַיָּם, יוֹצְאִין אַף עַל אִיָּר מִפְּנֵי פֶסַח קָטָן:

On six months messengers go out: On Nisan, because of Pesach; On Av, because of the fast; On Elul, because of Rosh Hashnanah; On Tishrei, to correct for the festivals; On Kislev, because of Chanukah; On Adar, because of Purim; And when the Temple existed, they also went out on Iyar, because of the little Pesach.


עַל שְׁנֵי חֳדָשִׁים מְחַלְּלִין אֶת הַשַּׁבָּת, עַל נִיסָן וְעַל תִּשְׁרֵי, שֶׁבָּהֶן הַשְּׁלוּחִין יוֹצְאִין לְסוּרְיָא, וּבָהֶן מְתַקְּנִין אֶת הַמּוֹעֲדוֹת. וּכְשֶׁהָיָה בֵית הַמִּקְדָּשׁ קַיָּם, מְחַלְּלִין אַף עַל כֻּלָּן מִפְּנֵי תַקָּנַת הַקָּרְבָּן:

On two months they desecrate the Shabbat, on Nisan and on Tishrei. For in those months, they were sent out to Syria to correct for the festivals. And when the Temple existed, they desecrated Shabbat in all of them — to correct for the sacrifices.

This desire to synchronize the Hebrew Earthly and Martian calendars however creates a unique problem.

It doesn’t make sense to have Martians adopt an exact 24 hours schedule, because in short order the halachic times would be disconnected from the reality of Martian sunrise and sunset. But if we keep the the Martian day, the “sol”, it would quickly disconnect from the Earthly calendar. Something has to give.

Our suggestions so far, are as follows:

  1. Keep the Martian “sol” as the daily halachic time for determining the beginning and end of the halachic Martian day.
  2. Recalibrate the Mars calendar, so that an average of every month or two, a day is subtracted from the Jewish month. For example: If we were to start the Jewish Martian year of 5778 on Thursday 1 Tishrei just like on Earth, by the end of Tishrei Mars would be almost 20 hours behind of their Earthly counterparts. However, if we subtract Friday 29 Tishrei from the Martian calendar the correction would push them ahead a more reasonable 4 hours. The advantage of this system is that you can calibrate throughout the year to ensure that both Earth and Mars celebrate the Jewish holidays on the same day.

Below is a more graphic source sheet and explanation for those more visually inclined. Comments, feedback and suggestions are most welcome.


1 Martian Day = 1 Sol = ~24 hours, 39 minutes, 35.244 seconds.

After 36 Sols, Mars’ “date” is 24 hours ahead of Earth.

If there are ever Jews on Mars, it would be of value for the Jewish calendars to be synchronized as much as possible.

Jews everywhere should celebrate the Holidays more or less within the same 24 hour period.

Tractate Rosh Hashana, Chapter 1: Messengers were sent from Israel to the Diaspora to make sure the Jews of the Diaspora would celebrate the Holidays at the same time (Mishna 3). Witnesses to the New Moon would even desecrate Shabbat to advise the Court of the New Moon, because messenger needed to get to Syria to inform the community there (Mishna 4).

Comparison of Earth Days to Martian Sols. Note that after 36 Martian Sols, 37 Earth Days have already passed. Every 36 Martian Sols, Earth’s and Mars’ “dates” will be a full 24 hours off.


Proposed solution:

A. Daily schedule (Shacharit, Mincha, Arvit, etc.) follows Martian time.

B. Hebrew Months and Years synchronized with Earth. On average of every month or two, subtract one day from the Martian Chodesh (generally at the end of the Chodesh). Meaning the Chodesh will  be 29 instead of 30 days, or 28 instead of 29 days. This will insure that Holidays are celebrated on Mars and on Earth within 24 hours of each other.

C. Every seventh Sol will be Shabbat, so Earth and Mars will quickly be out-of-synch with regards to Shabbat timing.

Proposed solution to Earth/Mars date discrepancy: Subtract one calendar day from the Martian Hebrew month every 1 or 2 months to realign calendars.