Why does Birkat Hachamah take place once every 28 years?
According to tradition, the sun was created at the moment of the spring equinox which coincided with the first moment of the fourth day of creation. When the sun reaches this starting point again at the same time of day and on the same day of the week, we recite the Birkat Hachamah. According to the astronomical calculations of the 3rd century sage Shmuel, the length of a solar year is 365.25 days, or 52 weeks plus 1¼ days. It thus follows that precisely one year after creation, when the sun returned to its original position, it would be 1¼ days (one day and six hours) later in the week. After two years, it would be 2½ days later in the week. Only after 28 years, would the sun return to that position at the same time—at the onset of the “fourth day,” Wednesday.
