Wednesday morning (April 8, 2009/14th of Nisan 5769), a unique, once in 28 years blessing will be recited -- Birkat Hachama, the blessing of the sun.
The event that is being observed is calculated by Jewish tradition to be the anniversary of the creation of the sun on the fourth day of creation. (And God made the two great lights: the greater light to rule the day, and the lesser light to rule the night; and the stars. And God set them in the firmament of the heaven to give light upon the earth, and to rule over the day and over the night, and to divide the light from the darkness; and God saw that it was good. And there was evening and there was morning, a fourth day – Genesis 1:16-19.)
Since the sun was created on the fourth day of creation, we mark this event on the fourth day of the Hebrew week, which begins at sunset on Tuesday and ends at sunset on Wednesday.
The sages taught that God set the starting point of the earth's relationship to the newly created sun at the Spring equinox. Only once every 28 years does the Spring equinox (according to the Jewish calendar) occur on a Tuesday evening. The next morning, when the sun is visible, Birkat Hachama is recited.
Birkat Hachama initially consisted of the blessing alone. It has been expanded to include several Biblical and Talmudic verses related to the sun, as well as selected Psalms. The mitzvah itself, however, is fulfilled by simply pronouncing the standard blessing that is usually recited when viewing natural wonders: “oseh ma'aseh b'rei'sheet.” Blessed are you, Lord, Our God, Who effects the work of creation. This blessing should be recited before noon, and preferably before 3 hours of the day have elapsed (about 9:30 am depending on your location).
For a more detailed explanation of Birkat Hachama, along with the seasonal calculations, click here.