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When Rosh Chodesh falls on Shabbat, a special haftarah (Isaiah 66) is read.

However, in our fixed calendar certain months can never have Rosh Chodesh fall on Shabbat (Kislev, Sivan). For certain other months, the haftarah for Shabbat Rosh Chodesh is superseded by a different haftarah (Tishrei, Tevet, Adar (II), Nissan, Av).

Thus, the haftarah for Shabbat Rosh Chodesh can only be read for the months of Marcheshvan, Shevat, Adar I, Iyar, Tammuz, Elul.

(I’m aware that there are differing customs regarding Av and Elul; for the purposes of this question assume a community following the custom I have outlined here.)

My question is, what is the longest possible interval in the fixed calendar between readings of this haftarah?

We last read this haftarah in Iyar 5780, and will not do so again until Elul 5782, a gap of 29 months. Is that the longest possible interval?

Bonus: what's the longest interval between readings of the haftarah of Erev Rosh Chodesh?

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  • 1
    Turns out we're in the middle of the longest gap for Machar Chodesh too but you didn't notice :)
    – Double AA
    Dec 5, 2021 at 15:20
  • It so happens in this case many people didn't read it in Iyar 5780 so for them the gap this time is back to Elul 5779
    – Double AA
    Mar 6, 2022 at 13:35
  • Shabbat Shalom and Chodesh Tov, JoelK
    – Double AA
    Aug 26, 2022 at 12:18
  • @DoubleAA וכן למר
    – Joel K
    Aug 26, 2022 at 13:40

1 Answer 1

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Since this 29 month gap is longer than 24 months, we can limit our search to gaps that contain at least one complete year without the haftarah.

The only year type with no instances of this Haftara is זח״א Rosh Hashana on Saturday, no 30 Kislev, non-leap year (assuming the practice you mention for Shabbat Rosh Chodesh Av). Such a year is always immediately preceded by this Haftara being read on Rosh Chodesh Iyyar. Such a year is always immediately followed by a year beginning on Tuesday. Non-leap years beginning on Tuesday have this haftarah read for Iyyar while leap years beginning on Tuesday have this haftarah read for Elul (according to the practice you mention) which is longer, and hence is the longest possible gap.

For the reading of "Machar Chodesh", we also find only one year type that doesn't have it read at all, namely בח״ג Rosh Hashana on Monday, no 30 Kislev, non-leap year. Such a year is also always immediately preceded by this Haftara being read on erev Rosh Chodesh Iyyar. Such a year is always immediately followed by a year beginning on Thursday. Years beginning on Thursday always have this haftarah read on erev Rosh Chodesh Kislev. That gap is 5+12+2=19 months. But since that is less than 24 months we have to also search gaps that don't include an entire year without the haftarah.

Indeed we find in years זח״א beginning on Saturday, no 30 Kislev, non-leap year this haftarah is read for Marcheshvan. As above, such a year is always immediately followed by a year beginning on Tuesday. Non-leap years beginning on Tuesday have this haftarah read for Sivan while leap years beginning on Tuesday have this haftarah read for Iyyar which are both 8 months into the year. Hence we have a gap of 11+8=19 months. I believe that is the longest possible gap.

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  • The 19-month gap for Machar Chodesh also occurs from erev Rosh Chodesh Kislev of a החא (leap) year until erev Rosh Chodesh Sivan of the following year (which is a גכה non-leap), as documented in item P.6 here: individual.utoronto.ca/aribrodsky/5765.html Dec 5, 2021 at 19:46
  • @ari isn't that one month shorter ? there's two versions of thursday before tuesday and i thought they were both 18 months, maybe i miscounted
    – Double AA
    Dec 5, 2021 at 19:47
  • It's 19 months, since the החא is a leap year. Dec 5, 2021 at 19:50
  • It should be the same as השא where the next year is leap גכז the extra adar is in one of the two years doesn't matter which, @ari for some reason on my scratch paper here I wrote 18 but I think now you're right
    – Double AA
    Dec 5, 2021 at 19:57
  • You had another off-by-one, which I've now corrected. Dec 5, 2021 at 20:44

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