In Judaism, an hour is defined as 1/12 of the time from sunrise to sunset, so, during the winter, an hour can be much less than 60 minutes, and during the summer, it can be much more than 60 minutes.This proportional hour is known as a sha'ah z'manit (lit. A Jewish hour is divided into 1080 halakim (singular: helek) or parts.Welcome to Shabbbos Nachamu 2017 at the Hudson Valley Resort & Spa hosted by "Flakey" Jake -the man who knows over 10,000 people's birthdays!Join over 1,000 guests- including over 700 singles - ages 18 and up!(See International date line in Judaism.) The weekdays start with Sunday (day 1, or Yom Rishon) and proceed to Saturday (day 7), Shabbat.
Halachically, a day ends and a new one starts when three stars are visible in the sky.
While calculations of days, months and years are based on fixed hours equal to of a day, the beginning of each halachic day is based on the local time of sunset.
The end of the Shabbat and other Jewish holidays is based on nightfall (Tzeth ha Kochabim) which occurs some amount of time, typically 42 to 72 minutes, after sunset.
According to Maimonides, nightfall occurs when three medium-sized stars become visible after sunset.
By the 17th century, this had become three-second-magnitude stars.