THE BLESSING "OVER THE SUN at the beginning of its cycle," is to be recited in the ruin of the ancient synagogue at Masada:

Jews to Recite Rare Sun Blessing at Masada’s Ancient Synagogue

by Avraham Zuroff and Hana Levi Julian

(IsraelNN.com) For the first time in two thousand years, the ancient synagogue atop the Judean desert fortress of Masada will ring out at dawn with the rare blessing of the sun.

The blessing, recited only once in every 28 years, will be uttered by Jews around the world at the first appearance of the sun on the morning that precedes the Passover seder. Rabbi Shimon Elharar, director of the Dead Sea Chabad House, will lead a group in the sunrise ceremony atop the Judean clifftop fortress of Masada.

The Israel Nature Society at Masada has teamed up with Chabad to host a public celebration for the rare event, which will take place on Wednesday, April 8, at the time of the vernal equinox.

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Regarding the comments on the Roman siege of Masada later in the article, note that Josephus' account should be taken with a grain or two of salt. See here for links to commentary.

A more detailed description of the sun rite appears in the Jerusalem Post:

World of the Sages: The sun's new cycle

By LEVI COOPER

This coming Wednesday, on the eve of Pessah, we perform a ritual that occurs only once every 28 years. The source for this commemorative event is a passage in the Talmud (B. Brachot 59b). It records a tradition about blessings over astronomical events: "One who sees the sun at the beginning of its cycle, the moon in its mightiness, the planets in their orbits or the signs of the zodiac in their order, should say - Blessed are You, God, our Lord, King of the universe, who makes the work of creation."

Of the four astronomical events mentioned in the source, only one is commonly commemorated, that is "the sun at the beginning of its cycle." While the codifiers explain the other astronomical events - when the moon, the five planets visible to the naked eye and the constellations of the zodiac align in prescribed manners (see Maimonides, Laws of Blessings 10:18), it is not customary to recite the blessing over these events (Mishna Brura 229:9), perhaps because the calculations can only be made by a skilled astronomer and that task is beyond the ability of most people (Rabbi Ephraim Zalman Margoliot, 18th-19th centuries, Poland).

The blessing over "the sun at the beginning of its cycle" is, however, recited. "The beginning of its cycle" means the time that the sun returns to the position in the heavens which it occupied when it was first created.

The Talmud inquires: "When does it happen that the sun is at the beginning of its cycle?" The sage Abbaye responds: "Every 28 years the cycle begins again." Abbaye is referring to a major solar cycle; In truth the sun returns to its original position once a year, yet the blessing is prescribed for when the sun reaches its original position, on the same day and at the same hour of its original placement at the creation of the universe.

The sun was created and placed in the heavens on the fourth day of creation (Genesis 1:14-19), thus the blessing is always recited on the fourth day of the week - Tuesday night-Wednesday.

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UPDATE (16 April): More here.