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How was time measured for the purpose of Zmanim before we had accurate clocks like we do today? Was it possible to accurately determine Chatzos (at night) or the different watches of the night? I know the Gemara in Brachos suggests some ways to tell, but these seem to have more of a mystical significance than a physical one or at least I do not understand how someone could accurately determine time based on these at night.

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4 Answers

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Midday or midnight are relatively easy to determine for someone with a little astronomical awareness. When the sun is exactly due south - it's midday. When the constellation ("mazal") that is exactly opposite the sun's position on the ecliptic is due south - it's midnight.

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For nighttime, they could use water clocks.

[Jastrow (in the introduction to his dictionary, and under s.v. ארפכס) argues that one place in the Midrash (Bereishis Rabbah 4:4) and two in Mishnayos Kelim (14:8 and 30:4) refer to such a device, though most of the commentaries explain it as something like a funnel or a colander.]

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Chaim, well said. You can certainly consult a historian of timekeeping and there must have been some decent technology, but I strongly suspect that with regards to many things, it was about best effort; the Chayei Adam says as far as when shabbos ends, "wait until all doubt is gone from your heart."

Anything related to sunlight, people just looked up and had a good sense of it (which most of us no longer have).

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Tzait hakochavim and Alot HaShachar are different from other zmanim during the day in that a sundial is of no avail. – Chanoch Dec 7 '10 at 15:21
While I appreciate and like all of these answers, I guess what I am really wondering is did Chazal discuss Zmanim, were they really only speaking to the Jews of today who have digital clocks and watches? Or were they speaking to the Jews of their generation as well? Even if sundials and water clocks existed, how could Chazal expect them how to use Zmanim. Especially the different watches of the night for those who say special Tefilos at night. Thank you for brining this Chayei Adam which tells me that not everybody did have ways of measuring time accurately. – Chaim Dec 8 '10 at 7:40
As for watches of the night: that was something the culture took for granted, if you had overnight guard duty you took one of three shifts; it's not specifically a Jewish thing. (Judaism then said to use those times to coordinate your prayers.) So you could ask a historian how they measured them, probably by moon or stars or the like. – Shalom Dec 8 '10 at 17:55
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I think that quote from the chayei adam is found earlier in the shulchan aruch itself (OC 293:2) – Double AA Jul 27 '11 at 5:34
@DoubleAA, welcome to Judaism.SE, and thanks very much for that citation! I look forward to seeing you around. – Isaac Moses♦ Jul 27 '11 at 16:29
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up vote 3 down vote

I'd like to say a sundial, but I don't know enough about constructing sundials to know whether they tell time in fixed hours or proporitional hours, or whether there are different ways to construct them so that they could be made to serve either purpose.

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A sundial ain't gonna help you at night. – Isaac Moses♦ Dec 7 '10 at 15:26
Sundials tell time in fixed hours, but help find high noon (midday) anyway. – msh210♦ Dec 7 '10 at 18:36
But see books.google.com/… which talks about sundials that divide the daylight hours into 12 equal parts. – Chanoch Dec 8 '10 at 1:06
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