The answer to this question provides the key to many mitzvoth, such as how long to keep Shabbat, how long to fast, and when to light Hannukah candles. This series, rich with sources, enables you to avoid common halachic errors.

1. Hannukah

Many Jews light Hannukah candles at a time that halachically makes no sense. This secret is buried at the very end of this double-shiur.

Hannukah 1
You light Hannukah candles at sundown. But when exactly is that? The answer is not so simple.

Hannukah 2
There are only three ways of resolving this apparent contradiction in the Gemara.

2. Ending Your Fast

The time to end your fast, on every day except Yom Kippur and Tisha B'Av, is earlier than you may think. The proof is in P'sahim.

3. Rationale of Timing of Nightfall 

Here's the reasoning behind the decision of when nightfall begins. Rav Bar Hayyim explains an apparent contradiction in the Rambam.