A Jewish ceremony that happens once every 28 years will take place this month.

Birkat Hachamah, or Blessing of the Sun, is done according to calculations done by the ancient rabbis. The calculations showed that every 28 years — 10,227 days — the sun is in the same place in the heavens as when it was first set in motion during Creation.

It takes place 18 days after the vernal equinox. This year, that moment is on April 8, only the third time it has coincided with the day of the First Seder.

Some groups are planning ceremonies around the event. In New Orleans, Chabad will hold a program at Audubon Park at 8:30 a.m.

Beth Israel and Gates of Prayer in Metairie will assemble on the Lakefront at the foot of Canal Boulevard at 6:30 a.m. Rabbis Robert Loewy and Uri Topolosky will lead the service.

Interfaith Montgomery will hold a “Blessing of the Sun” at 7 a.m. at the Riverwalk Park band shell.

The program will involve prayers and songs celebrating creation, with a guest speaker to be announced later. Members of Interfaith Montgomery, representing many Christian denominations and the Jewish and Muslim communities, will also participate. None of the organization’s members ever recall a similar event in Montgomery.

By coincidence, the Montgomery Chorale has been working on “The Creation,” an oratorio by Josef Haydn. The Chorale will offer selections of the oratorio during the 7 a.m. event, accompanied by members of the Montgomery Symphony Orchestra.

Simple service

The blessing itself is short — “Blessed are You, Lord our G-d, King of the universe, who reenacts the works of creation.” It can be recited any time after sunrise until the first quarter of the day has ended.

The blessing may be said anywhere the sun is visible. If it is cloudy but the outline of the sun is still visible, it may be said. Otherwise it can be delayed until mid-day, but if it is still not visible at that point, the blessing is recited without mentioning G-d’s name.