This little-publicized feat of 19th-century architectural engineering - which a local archaeologist thinks friars used to mark the start of the Christmas season - has wowed visitors since its discovery just three years ago. And on the morning of Dec. 22, early risers can witness the light show, too.
"It's almost blinding," said the Rev. Edward Fitz-Henry, the mission's pastor. "Words can't really describe it. It's really wonderful."
The eerie spectacle begins at daybreak on Dec. 22 when the morning sun hits the front of the church.
A seemingly transfixed beam of sunlight penetrates the window above the choir loft. As if passing through a magnifying glass, it narrows and intensifies. It shines a 20-square-foot rectangular window of light onto the center aisle. The light crawls up the entire 180-foot length of aisle and then hits the main altar.
It begins at the left of the altar, and then passes across it to the right. All the while it illuminates the gold-leafed surface of the tabernacle, which is located atop the main altar platform.
"It lights up like a Roman candle," says CSU-Monterey Bay professor and archaeologist Ruben Mendoza. "It's brilliant."
After 20 minutes, the beam disappears.
That spectacle signals the winter solstice, which brings the longest night and shortest day of the year. That solstice has the shortest period of sunlight, because our hemisphere is leaning farthest away from the sun. Though the solstice does shift a bit, the longest night usually begins the evening of Dec. 21. The light show is the morning of Dec. 22.
Mendoza, who has been digging at the mission since 1995, said the phenomenon seems to be the work of church designers. Although he has not cemented his theory, he said the church alignment "looks too premeditated" to be chance.
Here's a link to a book on the subject: