Monday, November 20, 2006

Calculating Halachic Hours

Source: Halachic Times (with calculator)

The normal calendar that we use divides a day into 24 equal hours. Normally, noon is approximately the midpoint between sunrise and sunset, and of course midnight is approximately the midpoint between sunset and sunrise. This is thrown off, of course, by daylight savings time and other minor factors.

The "Jewish day" (daytime part) divides the time between sunrise and sunset into 12 equal parts that are often called "halachic hours". Since on average, sunrise is around 6am and sunset is around 6pm, we can call sunrise "Halachic 6am" and sunset "Halachic 6pm". This will then make it easy to describe the 12 halachic hours of daylight.

The times for morning, afternoon, and evening prayers are based on the notion of the halachic day. Also, the times for the start and end of the Sabbath, fasts, etc.. all use the Halachic day, although in some cases fixed times are used. For example, candlelighting on Friday night is always 18 real minutes before sunset, not 18 halachic minutes.

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