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Who knows twenty-eight?

Please cite/link your sources, if possible. After about one business day, I will:

  • Upvote all interesting answers.

  • Accept the best answer.

  • Go on to the next number.

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up vote 6 down vote accepted

The letters in יהא שמה רבא מברך לעלם ולעלמי עלמיא. It's also the number of words from יהא שמה until דאמירן בעלמא. Both are gematria of כח (strength), so the Ashkenazi minhag is that the communal response is 28 letters long, and the Sephardi minhag is that the communal response is 28 words long. The 28 word restriction is why לעלא מן כל becomes לעלא לעלא מכל in the Ashkenazi minhag during the 10 days of teshuva.

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Checkmark for related 28-ness over two different minhagim, gematria, and (via comment) Tanach. – Isaac Moses May 3 '10 at 15:52

28 years in the מחזור גדול, the long solar cycle, which is used for saying ברכת החמה

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28 are the "times" listed in Koheles (Ecclesiastes) 3:2-8: "there is a time to be born and a time to die," etc.

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And hence the words in the core of Kaddish. – Shalom Apr 30 '10 at 17:53
True, and now that you mention it, I think I've also seen someone who relates it to the 28-year cycle that Jeremy mentioned. – Alex Apr 30 '10 at 18:08
@Shalom: Could you expalin the Kohelet/Kaddish connection? – Chanoch May 3 '10 at 20:55

A couple of Beis Hamikdash-related ones:*

  • 28 amos (and four tefachim) was the length and width of the top of the Altar, in the second Beis Hamikdash (Rambam, Hil. Beis Habechirah 2:7), and it will be the same in the third Beis Hamikdash (may it be built soon!)

  • 28 amos was also the length and width of the base of the Altar, in the first Beis Hamikdash. (Middos 3:1, R' Yose)

  • 28 golden half-tubes (menakiyos) were used to hold up the 12 loaves of Lechem Hapanim ("showbread," or as they translate it in the Gutnick Chumash, "multi-surface bread") and allow air to circulate between them. (Rambam, ibid. 3:14)

  • 28-ply threads (six plies each of blue wool, purple wool, crimson wool, and linen, and four plies of gold) were used to weave the Kohen Gadol's efod (apron) and choshen (breastplate). (Rambam, Hil. Klei Hamikdash 9:5)

* Knowing how fond Isaac is of those. :)

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You realize, of course, that while engaging my interest makes your answer more likely to win, saying that you're doing so makes it less likely. (Not that you're hurting for rep points, in any case.) – Isaac Moses Apr 30 '10 at 18:42
Kicking myself for not thinking of the ply-threads; that one's in Rashi on Chumash. Alex, are you using Bar-Ilan for these? That's how I'd do it if I took this more seriously ... – Shalom Apr 30 '10 at 18:50
I use Tanach Plus, actually. But I try to stick to things that I already knew of (and just need to refresh my memory); it wouldn't really be fair to use it to get rep points for things that I never learned before. – Alex Apr 30 '10 at 21:30
Isaac - so this really is like the business world, huh? You have to express interest without showing that you're expressing interest. :) – Alex Apr 30 '10 at 21:32
It's perfectly fair to get rep points for sharing knowledge with the community and the world, whether it's new to you or not. – Isaac Moses May 2 '10 at 2:22

28 Iyyar is the day we got the Temple Mount back.

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28 is the length of each tapestry sewn together to cover the Mishkan, in Amot (cubits). This was enough to cover the top of the Mishkan and drape down over most of the two sides.

Rabbi Kaplan says something about this being the maximum size for a weavable tapestry. I think he means that they could make two 28 x 4s and sew them together, but not make a 28 x 8. Probably because 4 cubits is the average person's height (and therefore armspan), so it would be hard with a traditional loom to work with something wider.

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28 is the total perakim in the fingers of two hands.

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28 are the mishnayos in Uktzin

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