[Avodah] When Does the Day Begin and End According to Halacha?

[Micha Berger]

On Thu, Feb 18, 2021 at 01:04:17PM +0000, Prof. L. Levine via Avodah wrote:
> There is no simple answer to this question. The times could be different
> depending on where you live and the day of the year.
> 
> For a detailed discussion of this issue see
> https://seforimblog.com/2021/02/depression-angles/

Only end. The day begins at sheqi'ah. 0 minutes after sunset equals the
sun declining 0 degrees below the horizon. No difference in when the day
starts between computing a fixed interval or degrees below horizon.

In any case, computing tzeis isn't siginificantly more complex. It's as
easy to compute sunset (0 deg below the horizon) and add 36 minutes as
it is to compute when the sun is 7.12 deg below the horizon.

See the page I wrote at http://aishdas.org/luach
Or the widely used http://mysmanim.com
Both use declination. But I like my formatting. One page per month in
normal 7x4 or 7x5 calendar format. At the cost of not having every zeman
published for every day, and having to split the difference between the
zeman as it was two days before today and two day after. (I even threw
in the Molad on days that have one. One known bug -- doesn't know which
cities light 40 min before sheqi'ah.) Suggestions invited.

Tir'u baTov!
-Micha