Overview
Chatzos (חצות), meaning "midpoint" or "half," refers to halachic midday — the exact midpoint of the day when the sun is at its highest point in the sky. This is also known as solar noon or solar transit.
Calculation
According to most authorities, chatzos is calculated simply as:
Midpoint between sunrise and sunset
For example, if sunrise is at 6:00 AM and sunset is at 6:00 PM, chatzos is at 12:00 PM. If sunrise is at 5:30 AM and sunset is at 8:30 PM, chatzos is at 1:00 PM.
This time changes slightly from day to day based on the times of sunrise and sunset.
Alternative View
Rav Moshe Feinstein (Igros Moshe OC 1:24, 2:20) had a unique approach, arguing that halachic midday occurs at a fixed solar time throughout the year — approximately when the sun crosses the local meridian.
The Aruch HaShulchan (OC 233:14) similarly writes that midday is always at solar noon (12:00 solar time). This comes to approximately:
- 11:56 AM in New York
- 11:37 AM in Jerusalem
However, the prevalent practice follows the calculation based on the midpoint of sunrise and sunset.
Halachic Significance
Chatzos is significant for several halachos:
1. Prohibition of Chametz on Pesach Eve
From chatzos on Erev Pesach, it is forbidden to possess chametz. This is when the issur hana'ah (prohibition of benefit) begins.
2. Latest Time for Shacharis (B'dieved)
If one missed Sof Zman Tefillah (the fourth hour), they may still daven Shacharis until chatzos. After chatzos, one may not daven Shacharis.
3. Beginning of Mincha
Mincha Gedola begins half a sha'ah zmanis after chatzos (approximately 30 minutes). Chatzos itself is too early for Mincha.
4. Korban Pesach
The Korban Pesach could only be brought after chatzos on the 14th of Nissan.
5. Bris Milah
While a bris should ideally be done in the morning (zerizin makdimin l'mitzvos), it is valid all day until sunset. Some have the custom to complete it before chatzos.
Chatzos at Night (Chatzos Layla)
Chatzos Layla (midnight) is exactly 12 hours after chatzos hayom (midday), according to most authorities.
This is significant for:
- Tikun Chatzos — the midnight prayer lamenting the destruction of the Temple
- Latest time for Krias Shema at night according to some opinions
- Beginning of time for certain mitzvos of the following day
Technical Note
The time of chatzos stays relatively constant from day to day (varying by only about 30 seconds maximum). The "Equation of Time" causes the solar day length to vary slightly throughout the year, but the effect on chatzos is minimal.