Yoma 3:1-2

Yoma 3:1

Here we begin the description of the Yom Kippur service. First, a Temple official instructed the kohanim to go see whether the time to slaughter the morning tamid offering had arrived. If it had, the one checking announced that dawn had broken. Matisyahu ben Shmuel said that they didn’t slaughter the tamid until the person checking reported that the entire east was lit. They would ask him if that included Chevron (Hebron) and he would confirm that it did.

Yoma 3:2

Why was it necessary to send someone to check for the dawn? Because on one occasion (not on Yom Kippur), the light of the moon made them think that it was dawn. They offered the tamid and, when they discovered the mistake, they had to take it out to be burned. Resuming the description of the Yom Kippur service, they would bring the Kohein Gadol to the place where he would immerse. The general rule was one who evacuated his bowels in the Temple had to immerse in a mikvah and one who voided his bladder had to wash his hands and feet.