Birkat Hachama (ברכת החמה, "Blessing of the Sun") refers to a Jewish blessing that is recited on the Sun once every twenty-eight years, when the vernal equinox as calculated by tradition falls on a Tuesday at sundown.

When the sun returns to the same position, at the same time of the week, that it occupied at the time of its creation, we recite a special blessing. We will perform this mitzvah this year on April 8, 2009.

According to Judaism, the Sun has a 28 year solar cycle known as machzor gadol (מחזור גדול, "the large cycle"). A solar year is 365.25 days long and the "Blessing of the Sun", being said at the beginning of this cycle, is therefore recited every 10,227 (28 times 365.25) days. The next time that it will be recited will be on April 8, 2009 (14 Nisan 5769 on the Hebrew calendar).

The same blessing is recited upon experiencing various natural phenomena, including lightning, comets, and meteor showers; as well as upon witnessing wondrous natural topography, such as great mountains, rivers and vast wilderness.[Artscroll Yitzchak Yair Siddur page 98] When recited for these other experiences, the blessing is recited alone without additional verses or Psalms etc. The text of the blessing itself is as follows:

"ברוך אתה ה’ אלוקינו מלך העולם עושה מעשה בראשית"

"Blessed are You, HaShem, our God, King of the Universe who makes the works of Creation"

Overview

According to the Babylonian Talmud,[Bavli Berachot 59b] the Sun makes a 28 year cycle to return to the position that it was in when the Universe was first created. According to Jewish tradition, the Sun was created[Genesis 1:14 + commentary of Rashi. Many Biblical commentators, including Rashi, insist that the luminaries were, in fact, created on the first day and only suspended in place on the fourth day.] on the fourth day (יום רביעי, yom rivi’i) of the week of Creation. Because Jewish law considers the time unit of a day to span from evening to evening, the beginning of the halachic fourth day, so to speak, is on Tuesday evening at sundown. The 28 year cycle therefore begins and ends at the point in time when the Sun was created, this being sundown on Tuesday. The Sun only returns to this exact position at sundown on a Tuesday once every 28 years. Despite the rigorous calculations that follow, there is no synchronization of this prayer and the actual astronomical point in time when the sun crosses the celestial equator; the symbolism is no different than a situation in which the molad for Tishrei would fall out by day on a Sunday and Rosh Hashanah falls out on Monday.

Mashiach

This prayer also makes reference to the future days of the Messiah and the fulfillment of all prophecy, when “the light of the sun will be seven times brighter…on the day HaShem binds up the fracture of His people and heals the bruise He has inflicted” (Isa. 30:26). In the last days, when the “sun of righteousness” (Mal. 4:2), or Messiah, will sit on his throne in Jerusalem, He will heal the fractures and bruises of His people through the power of his God, the God of Israel.

In another note, there is a similarity between shemesh and shamash, we are given a proper perspective of the sun’s role. It is not a god to be worshipped but is a servant that we can thank God for.

Video on Birchat Hachama: David Solomon on Birkat Hachama 101