# How is Chatzos Halayla (Halachic Midnight) calculated?

It seems pretty easy to calculate from the get-go that the formula is something like this:

``````# a halachic hour is one twelfth of the time between sunrise and sunset
halachicHour = (timeOfSunset - timeOfSunrise) / 12
# thus chatzos halayla would be literally
chatzosHalayla = timeOfSunset + (halachicHour * 6)
``````

Above, a halachic hour is determined by the distance from sunrise to sunset divided by twelve.

This makes things interesting, as I presume that often "midnight" doesn't exactly happen in the middle of the night (period between nightfall and sunrise or dawn). How, then, do we calculate Chatzos Halayla?

I was reading a book on Tikkun Chatzos recently which sparked my interest in this. According to the author, Rebbe Nachman of Breslov calculated the middle of the night by adding six civil hours to nightfall, but this doesn't make any sense and I believe that the author is making an assumption about this. It would make sense to say that Rebbe Nachman calculated the middle of the night using six halachic hours, but to use six civil hours doesn't really make any sense to me.

• My understanding is that Rebbe Nachman zy'a rules this way to make things easier to calculate. He may be basing himself on the Mechaber as is general practice in Breslev.
– yoel
Commented Sep 22, 2011 at 1:05
• His cheshbon is: take tzeis hakochavim and add a quarter of a me'eis l'eis. What's wrong with that?
– user12918
Commented Jul 10, 2016 at 2:43
• In Book "The Sweetest Hour" by A. Greenbaum, author says that Rabbi Nachman's opinion is according to MA in OC 1:2 and 233:1. Commented Dec 6, 2017 at 16:46

• Re "in any case...": There are differences of opinion as to when chatzos (day or night) is. IIRC Rabbi Moshe Feinstein's view is that chatzos (or at least one of them) is constant (over the course of a year for any given location), which would not fit in with its being 6 hours into the night. I don't know (or don't recall) what particular constant he said it is, though. `:-/` Perhaps someone else can answer better. Re "12:46 am and pm": If chatzos is 6 hours into the night/day, then they will be 12 hours apart (plus or minus about a minute) on any given day just because of arithmetic.