I would like to make my own Jewish calendar on paper with pencil ( using the help of programming for the more difficult calculations, ofcourse). How and where do I begin.
Who makes the annual Jewish calendar? Who exactly checks to make sure that all the leap years, etc are added as they are supposed to. Is there a "Hashgacha/ Mashgiach" for the calendar?
There's no need for a mashgiach since anyone can check on their own. Here's all you need to know to calculate any date.
In years whose value is 0,3,6,8,11,14,17 modulo 19 an extra month is added after Shevat with 30 days.
The "molad" (new moon occurrence) of Tishrei of year 1 was 5 and 204/1080 hours into the second day of the week. Every subsequent molad happens 29 days and 12 and 793/1080 hours later.
Rosh Hashanah for a given year is the day its molad falls, unless pushed off by one of the following four rules. 1) Rosh Hashanah would be the first, fourth or sixth day of the week, 2) the molad is 18 hours or more into the day, 3) at the start of a leap year, that number for the third day of the week is 9 and 204/1080 hours into the day, 4) when following a leap year, that number for the second day of the week is 15 and 589/1080 hours.
The non-leap months alternate lengths between 30 and 29 beginning with Tishrei, but you should add a 30th day to Marcheshvan or remove the 30th day of Kislev as necessary to ensure the right number of days exist between Rosh Hashanah of one year and the next.
My father,the tzaddik nistar Harav Shraga Feivel ben Chaim Yehudah , made his own calendar using the Rambams rules as written in the Perush L'Mishnayos, when he was exiled to Siberia in 1939 at th age of 20. I thought it looked like our tradiitonal calendars. What a mistake. It was a strip of paper with the rules written on the bottom, the years running alongside vertically , and the hebrew dates of all the yomin Tovim next to each year. Interestingly, he had no idea when the Churban would be over, so he ran it to 2011, the very year he was Niftar. Tzaddik Gumer. Shochet with 3 smichos before he was 18, built Mikvah in Toulosue France in 1948, still there, made Kosher meat and chicken and learned 5 hours a day while working in USA. Zatzal.
For a detailed walk through the process, for 5780, here's my youtube presentation: https://www.youtube.com/channel/UC8L25iBp_ZUias3gnvtFJTA
Here is a folder available of the apps used: https://sites.google.com/site/miyminimichoel/home/this-years-calendar Comments welcome.