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Kiddush Levana

6 months ago • updated by 3 days ago • 3

It would be great if there was an option to show the latest time to say Kiddush Levana as a calendar event

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Started

Hi Mendel, shana tova!

The calculations have been added to our open-source library, @hebcal/core. It has the earliest time (3 or 7 days after the molad) and the latest time (either halfway between one molad and the next, per the Maharil and Rema, or a full 15 days, per the Shulchan Aruch). Each time can also be moved out of the daytime, since Kiddush Levana is only said at night. What's left is deciding how to show it on the website and in the calendar feeds.

The latest time is set by the molad, which is the same moment worldwide, but the night you're in depends on where you are. So the event will need a location, the same way candle-lighting times do.

There are 4 different possibilities of what to show

Method	Rule	Opinion
Earliest 3d	molad + 72h	Rabbeinu Yonah. Common Chabad and Sephardi practice
Earliest 7d	molad + 168h	Mechaber (Shulchan Aruch)
Latest halfway	molad + 14d 18h 22m 1.666s	Maharil and Rema, halfway between moladot
Latest 15d	molad + 15 × 24h	Shulchan Aruch OC 426

A big part of why we haven't made more progress on the hebcal.com / calendar feed side is the fact that there are so many different halachic opinions. Which do you observe? What does Hebcal choose to show? We do not want to add a UI that has a dozen different choices.

To make it more concrete, if we look at New York for the past month and upcoming:

Month	Earliest, 3 days	Earliest, 7 days	Latest, Maharil	Latest, 15 days
Tishrei 5787	Mon 14 Sep 8:18pm (moved to tzais)	Fri 18 Sep 8:11pm	Sat 26 Sep 5:35am (alos)	Sat 26 Sep 5:35am (alos)
Cheshvan	Wed 14 Oct 3:22am	Sun 18 Oct 3:22am	Sun 25 Oct 9:44pm	Mon 26 Oct 3:22am
Kislev	Thu 12 Nov 5:52pm	Mon 16 Nov 5:49pm	Tue 24 Nov 5:41am	Tue 24 Nov 5:41am
Tevet	Sat 12 Dec 3:50am	Wed 16 Dec 3:50am	Wed 23 Dec 10:12pm	Thu 24 Dec 3:50am

Would we show all 4 in the calendar feed? Or in the case where the latest time collapses to alot haShachar, 3 events?

Or two events -- one for the earliest on day 3 (with a note giving the time for people who observe day 7) and one for the latest? Or a single all-day untimed event on the Earliest, 3 days option that contained all of the exact times in your local timezone be better?

What about a timed event at 3:22am... would you really want your calendar to buzz you at that time? And what if the latest KL is on Shabbat -- do you want a reminder going off on Shabbat or does it have to move to Friday?

Planned

6 months ago

Thank you for this suggestion, we will look into implementing this after Pesach

4 days ago

Hi, I'm wondering if there's any update on this?

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