A Beam of Light on Winter Solstice
By Ruben G. Mendoza, Director Institute of Archaeology,
California State University Monterey Bay
By Ruben G. Mendoza, Director Institute of Archaeology, California State University Monterey Bay On Winter Solstice, December 22, 2001, while archaeologists waited and watched, a solar beam of light poured through a window and illuminated the golden tabernacle of the main altar of the Old Mission Church at San Juan Bautista. The event was not accidental, but was carefully designed into the early Mission when it was first constructed.
While we in the age of atomic clocks, electronically precise instruments and a more or less accurate Gregorian calender, see little need to rely on astronomical phenomenon for charting the passage of time, that was clearly not the case in the late 18th and early 19th centuries when the church of San Juan was constructed. At that time, the Vatican and its Roman Catholic priesthood was obsessed with charting the passage of time using church interiors as both meridian-based observatories and as camera obscura-like architectural instruments. Careful design, mathematics and construction let them chart the suns transit through the heavens; project the actual dimensions of the solar orb; and measure the relative relationships of fixed architectural monuments to both the winter and summer solstice events. Of particular concern to the Padres of the time, was accurately noting the day of the winter solstice and thus identifying the exact dates for the commencement of the Christmas season.
As much of my archaeological research at this time is being done on the San Juan Bautista Mission complex, I asked Joe James, a surveyor from Monterey, California to assist me in an electronic mapping and survey of the main alter complex and layout of the main Church. He agreed to volunteer his time to the project and was with me as we waited to see the phenomena and map an accurate trajectory for the lightfall.
As a result of this work we were able to determine that the San Juan Bautista Mission Church and several architectural features at the site were designed to function as a solar meridian for charting the passage of the winter solstice. We will be back in June to see what is illuminated on the summer solstice.
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