I understand that Jewish astronauts have been advised to observe Shabbat by Cape Canaveral time, by analogy with traveling to a place that doesn't have daily sunrise/sunset where some rule you use the last place you were that did. But this seems to describe a temporary journey, such as a shuttle flight. What is the rule if one is living in space for an extended time? Edit: Would each individual determine his own time (if it's based on home/departure city), or would the community living there determine a time together to reduce the chaos of varied Shabbat times in the same place?

(This is related to this question and this question, but these questions are about earthly sunset-less days, which might be different.)

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    Maybe shabbat doesn't apply in space. In fact, maybe mitzvot don't apply there. I remember seeing an article where the author suggested (semi-seriously) that the source for mitzvot outside of Israel is a passuk which says "adama", and therefor might does not include outer space. CYLOR before grabbing a ham sandwich though;)
    – Ariel K
    Aug 3, 2011 at 22:23
  • I'm not sure why nobody does this, but if I was asked this question, I would first look up what Astronauts do, and how they set time for their sleep cycle.
    – avi
    Aug 4, 2011 at 7:59
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    The answer is simple: "Torah: Lo BaShamayim Hee"! Hence, no shabbat observance necessary in space :-) Same applies to the rest of mitzvot!
    – user2261
    Jan 7, 2013 at 20:30
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    Wasn't there a kuntros put out for Ilan Ramon a"h?
    – MTL
    May 25, 2014 at 4:07
  • 2
    Went looking for that kuntros, and found this website ...looks like a good resource for questions like these ;)
    – MTL
    May 25, 2014 at 4:08

4 Answers 4


Again. If living someplace where there is no concept of sunrise/sunset at all, the opinions are:

  • Follow your hometown
  • Follow the last normal place you'd been (in this case, Florida)
  • Follow Jerusalem
  • Follow an artificial 6AM-6PM clock, using whatever timezone you have.
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    Does it change if you take up residence there? Would a space colony be expected to settle on a single community standard, or would you have American and Chinese and Russian astronauts following different standards in the same place (which sounds impractical)? Aug 3, 2011 at 16:37
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    @Monica, the practicality of any solution in that eventuality is essentially irrelevant right now, given the number of places on the globe that presently have Halacha-followers in space. If it ever becomes an issue, the practical solution will probably involve everyone up there agreeing to ask one rabbi, and that rabbi coming up with a solution that makes practical sense.
    – Isaac Moses
    Aug 3, 2011 at 17:42
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    @Monica, why should a space colony be more homogeneous than us Earthlings? :)
    – YDK
    Aug 3, 2011 at 19:46
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    @YDK, fair enough, but at least in any given city everybody agrees, within an hour or so, when Shabbat is. Things might get trickier if within a single "city" in space you've got a 12-hour spread based on hometowns. So they should just agree on Jerusalem or 6AM-6PM days, if they could actually agree on anything. :-) Aug 3, 2011 at 20:36
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    @tomsmith, see star-k.org/kashrus/kk-whendoesonepraywhenthereisnoday.htm . "Hometown" is Tiferes Yisrael; 6-6 is Ben Ish Chai. Jerusalem and last-normal-place visited were also given as answers (don't recall by whom) when Ilan Ramon ah's asked. (I think I saw that one in jpost a while ago.) Last-normal-place visited is similar to "closest-normal-place", which is what someone online said was RM"F's answer in one instance. (Again that's hearsay) ... this is fun as the South Pole would, depending on your rabbi, follow either Jerusalem or Christchurch!
    – Shalom
    Sep 19, 2011 at 2:55

You might first ask, Rabbi Ben-Zion Firrer asked, whether the mitzvahs are required at all in space. After all, the Torah says that you should do the commandments "all of the days which you are alive on this earth" (Deut. 12:1), maybe we aren't obligated to perform the commandments in space or on the moon. Rabbi Shlomo Goren, in an interview published in HaZofeh (and republished in J.David Bleich, Contemporary Halakik Problems, Vol. I, at 211) reasoned that since one cannot survive in the environment of space without bringing earthly oxygen and water with him, he is still "on this earth" for purposes of this, now, very real discussion.

The simple answer is that when outside of the earth's atmosphere, normal measures of time, such as sunrise and sunsets, and lunar rotations that help us count the months, are useless. Therefore, one would designate the time and calendar events that occur in his home port, e.g. Houston or Cape Canaveral. One would do much the same thing if going to the North or South Pole. Much of Rabbi Bleich's article is available on Google Books. Also see the Keren B'Yavneh website which has some papers on the subject, although I don't think any are in English.


Based on this article: I would say that people in the ISS would keep Shabbat based on the location of the place they will be landing when they come back, or based on the location of the earth crew that is working with them. This is how the people aboard the ISS mantain their daily lives, and it would be peculiar to do it another way.


Rav Moshe Sternbuch shlit"a has a teshuva about in Teshuvos v'Hanhagos 5:84. There, he rules that the Torah was meant to be observed on earth, and that the concept of Shabbos etc. doesn't really exist in space. (He writes that it is forbidden to remove oneself from the obligation to keep mitzvos, and thus it is prohibited to go to outer space.)

He further writes that a person should designate one day to keep as Shabbos. He says that although one could theoretically pick any day, and "some" suggest to keep it based on one's last location on earth, he personally feels one should observe Shabbos like Eretz Yisrael.

After writing this, I found this very useful source booklet online compiled by Rabbi Avraham Manning. He brings citations from numerous sources discussing the issue of mitzvos in space travel, including Rav Sternbuch's teshuva. He does a very thorough job of walking the reader through the various issues involved and the relevant opinions.

  • Btw it's Sternbuch with a sin. (For much of my life I also didn't know that) hebrewbooks.org/pdfpager.aspx?req=41193&st=&pgnum=2
    – Double AA
    Mar 23, 2021 at 23:58
  • That's very interesting that he spells his name that way in English. In Hebrew it's always pronounced with a shin. (I guess it's similar to Rav Moshe Feinstein, whose name is usually pronounced with a shin in the yeshiva world.) thanks for sharing this.
    – Binyomin
    Mar 24, 2021 at 0:10
  • I edited it. but maybe keep your comment so people can see your reference. A lot of people make the same mistake that i did.
    – Binyomin
    Mar 24, 2021 at 0:13
  • It should be clear that R' Sternbuch shlit"a limits this to mitzvos that relate to time, being as the passage of time in outer space has different rules to that on Earth. Of course, all other mitzvos are obligatory.
    – chortkov2
    Jan 16 at 21:43

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