The night of the 24th of December is known as “Nittel Nacht.” On this evening, there is an extra measure of kelipa in the world due to the events commemorated by other nations on this day.

The timing of Nittel Nacht does not follow the Jewish calendar, but rather the secular calendar. As the Rebbe explained in multiple letters (see Likkutei Sichos Vol. 15, pg. 554; Igros Kodesh Vol. 13, pg. 120; and Vol. 14, pg. 352), the date must be determined by the observance of the local non-Jewish population. 

The Jews of each country observe this custom on the eve of yom eidam (literally “the day of their calamity,” used as a metonymy for their festival) as it is celebrated by the non-Jews of that country.

The Rebbe pointed out that the Frierdiker Rebbe said that in America, one should mark Nittel on the day that the local population celebrates.

This leads to different dates depending on which calendar the local population uses:

 In the United States and most of the Western world, the majority of the population follows the Gregorian calendar. Because their holiday is celebrated on December 25th, the Jewish community observes Nittel Nacht on the eve of that date.

In Russia and many other Eastern European countries, the majority population follows the older Julian calendar. Since that calendar is 13 days behind, their holiday falls on January 7th. Following the local custom, Jews in those regions have historically marked Nittel Nacht on the eve of January 7th.

In a location with variances in the dates for the non-Jewish yom eidam, the Rebbe states that Nittel Nacht is observed on the date that the majority of the local non-Jews celebrate.

Historically, Ukraine followed the Julian calendar like its neighbors, so Nittel Nacht was always observed on January 7th. However, in 2023, the Ukrainian government, led by President Volodymyr Zelenskyy, officially moved the holiday to December 25th to align with Europe and move away from Russian influence due to the ongoing war. 

Although there are still minorities in Ukraine who celebrate on January 7th, the “majority” and the “official” date in Ukraine has now changed. Consequently, the timing for Nittel Nacht in Ukraine has shifted to December 25th as well.

It is interesting to note how President Zelenskyy, a Jew himself, effectively has the power to determine the day on which Jews in Ukraine will mark Nittel according to Halacha.

As in many communities, the minhag of Chabad is to refrain from learning Torah from nightfall until midnight. The reason for this is to avoid adding vitality to the forces of impurity.

The Rebbe relates that the Rebbe Rashab was careful not to learn Chassidus and was particular about other aspects of his conduct on this night. 

In a sicha on Shabbos Parshas Veyeshev 5750, the Rebbe said we should utilize the time of Nittel for practical benefit. It is appropriate to use this time for matters that lead to increased wisdom, such as playing chess, which sharpens the mind. One should also increase in acts of tzedakah and chesed, or use the time to take care of the home.

In that same sicha, the Rebbe specifically mentions sewing clothing and, l’havdil, picturing the Rebbe’s face in your mind – noting that this applies whether you saw him in person or only saw a photograph. 

For these reasons, many maintain the custom to play chess on Nittel Nacht.