But what is Yom Kippur and how is it celebrated? Yom Kippur will be observed from sunset on Wednesday, Oct. 1 until after nightfall on Thursday, Oct. 2. In the Jewish faith, shofar horns have been used for centuries for various purposes, including proclaiming the Sabbath. People celebrating Yom Kippur typically say to each other the Hebrew saying “Gemar chatimah tovah," which translates to “A good final sealing.” It comes from the idea that on Yom Kippur, their fates for the year ahead will be finally sealed. However, it is not common to wish someone a "Happy Yom Kippur."