section_path: Components/Hours
section_name: Hours
paragraph_text: Hours
  
  Judaism uses multiple systems for dividing hours. In one system, the 24-hour day is divided into fixed hours equal to 1 ⁄ 24 of a day, while each hour is divided into 1080 halakim (parts, singular: helek). A part is 3 + 1 ⁄ 3 seconds (1 ⁄ 18 minute). The ultimate ancestor of the helek was a Babylonian time period called a barleycorn, equal to 1 ⁄ 72 of a Babylonian time degree (1° of celestial rotation). These measures are not generally used for everyday purposes; their best-known use is for calculating and announcing the molad.
  
  In another system, the daytime period is divided into 12 relative hours (sha'ah z'manit, also sometimes called "halachic hours"). A relative hour is defined as 1 ⁄ 12 of the time from sunrise to sunset, or dawn to dusk, as per the two opinions in this regard. Therefore, an hour can be less than 60 minutes in winter, and more than 60 minutes in summer; similarly, the 6th hour ends at solar noon, which generally differs from 12:00. Relative hours are used for the calculation of prayer times (zmanim); for example, the Shema must be recited in the first three relative hours of the day.
  
  Neither system is commonly used in ordinary life; rather, the local civil clock is used. This is even the case for ritual times (e.g. "The latest time to recite Shema today is 9:38 AM").