Chatzos Halaylah – Middle of the Night

(שמות יא, ד) וַיֹּאמֶׂר מֹשֶׂה כֹה אָּמַר ה' כַחֲצֹת הַלַיְלָּה אֲנִי יוֹצֵא בְתוֹךְ מִצְרָּיִם:

Many laws are determined by the halachic declaration of the middle of the night

• Tikkon haChatzos – special individuals sit and mourn the destruction of the Bais HaMikdash. (Sanhendrin 16a relates that Dovid haMelech had a harp that made a noise at Chatzos HaLaylah to awaken David to learn Torah)
• Eating the first Ke’zeis of Matzah on the first night of Pesach to be done before Chatzos HaLaylah
• Eating the Korban Pesach and the Afikomen on the first night of Pesach prior to Chatzos HaLaylah
• Eating the first Ke’zeis of bread on the first night of Succos to be done before Chatzos HaLaylah
• Rabbinical decree to say Kreias Shema prior to Chatzos HaLaylah
• Custom to not say Selichos at night till after Chatzos HaLaylah
• Custom to not say Tehillim at night till after Chatzos HaLaylah
• Custom to not learn Tanach at night till after Chatzos HaLaylah

Three different opinions regarding the halachic time of the middle of the night:

1. Shaari Tzion: Considers the middle of the night to be exactly 6 hours after the beginning of the night, with no difference whether it is summer or winter.
   Example: If the night begins at 8:00 P.M., then the middle of the night is 2:00 A.M.
   If the night begins at 5:00 P.M., then the middle of the night is 11:00 P.M.
2. Mishneh Berurah & Shulchan HaRav: The night is divided into 12 halachic hours and at the end of the sixth hour is the middle of the night. Since the hours in the day are also divided into 12 halachic hours, Chatzos of the night is the same middle time as Chatzos of the day. Thus, if the middle of the day is 12:30 P.M., then the middle of the night is 12:30 A.M.
3. Ateres Tzvi & Bnai Yissachor: Always set the middle of the night at 12:00 midnight (except in Yerushalayim which sets the time at 11:40 P.M.)