The observance of Jewish law (halakhah) in the polar regions of Earth presents unique problems. Many mitzvot, such as Jewish prayer and the Sabbath, rely on the consistent cycle of day and night in 24-hour periods that is commonplace in most of the world. However, north of the Arctic Circle (and south of the Antarctic Circle) a single period of daylight can last for a month or more during the summer, and the night lasts for a similar length of time in the winter. The question for religious Jews that live in or visit these regions is how to reconcile the observed length of days in the polar regions with common practice elsewhere in the world. Should a "day" be defined solely based on sunrise and sunset, even if these events do not occur for long stretches of time, or should the definition of a polar "day" be consistent with the length of a day in the rest of the world?
The problem was first identified in the 18th century, when Jewish émigrés began to move in greater numbers to the northern parts of Scandinavia. A number of different opinions on the question have been presented in responsa and are reviewed in a 2005 essay by Rabbi J. David Bleich,[1] and in a 2007 article by Rabbi Dovid Heber.[2]