Two days ago, on the Feast of the Assumption, a remarkable and very cool thing happened at Mission Nuestra Señora de la Purisima Concepción de Acuña in San Antonio, Texas—at least it happened if the skies were clear. The sun illuminated the floor in front of the church’s altar, and the wall behind the altar, in a particularly cool fashion, at around 6:30 pm local time. This sort of illumination happens every Feast of the Assumption, and has recently become somewhat famous in San Antonio, gathering some attention from local media in the past few years.

Mission Concepción is one of a series of missions established by Spanish Franciscans along the San Antonio River during the early eighteenth century. The church was completed in 1755. The San Antonio Missions are today active Catholic churches in the Archdiocese of San Antonio, while also being part of the San Antonio Missions National Historical Park, and a UN World Heritage Site.

The story of those parts of America that were colonized by the Spanish is considerably different from the story of those parts of America that were colonized by the English. There are at least two big differences that strike me. Both have to do with the native populations in areas the Spanish sought to colonize.
I began to understand something about the first difference during the 500th anniversary of Columbus’s arrival in the Americas. An article in a “Fall/Winter 1991 Columbus Special Issue” of Newsweek magazine discussed something the Spanish know as la leyenda negra—the Black Legend—that portrays the Spanish as “incomparably savage and avaricious”. The point of the article was to argue against la leyenda negra. It quoted Woodrow Borah of the University of California, Berkeley as saying, “The Spanish made a place for the Indians—as part of the lowest order, but at least they had a place. North Americans in many cases simply exterminated the Indians.” And it noted that today Native American ancestry is common among people in areas that were part of Spanish rule. By contrast, in my home state of Kentucky, for example, very few people can claim descent from the native Shawnee who lived along the Ohio River in the eighteenth century. Indeed, for most of the past two and a half centuries this area that was once a county of the English Virginia colony has been populated by people who claim only European or African ancestry. Native people survived in places where the Spanish colonized, in a way that they did not in places like Kentucky.
A visit I made some years later to Castillo San Marco in St. Augustine, Florida highlighted this Spanish difference. A ranger with the National Park Service emphasized that at St. Augustine there was a different African American history than the one most Americans are familiar with. Slaves of African descent would escape from the English colonies and make their way south to Spanish Florida, where they could be free, and were given land, trained in the use of weapons, and manned Ft. Mose, an African-American community that formed the northern outpost of defense for the Spanish colony.
Thus the first of the two big differences I mentioned above, between the story of the parts of America colonized by the Spanish, and those parts that were colonized by the English, is how the Spanish interacted with other peoples in the New World. This is not to paint a rosy picture of the Spanish, but it seems that in Spanish areas, non-Spanish people could live in community with the Spanish, and even share in defense, and native people survived.
The issue of defense pertains to the second big difference. In an area like Kentucky, the story of conflict between European immigrants to the area and the native people who lived in the area really goes only one way—the Europeans won, the natives lost. This was not true in Texas in the eighteenth century. Some native people, such as the Commanches and the Apaches, were able to adapt the horse, which the Spanish introduced to the New World, and new weapons, to become powerful horse-mounted-warriors. They were able to drive back the Spanish in some places, and to be a decades-long threat to Spanish holdings in others. They were also a serious threat to other native peoples, such as the Coahuiltecans who dwelled in the areas near the San Antonio River.
Thus the various interpretive panels that can be found among the San Antonio Missions describe the missions as follows:
The missions of San Antonio were far more than just churches, they were communities. Each was a fortified village, with its own church, farm, and ranch. Here, Franciscan friars gathered native peoples, converted them to Catholicism, taught them to live as Spaniards, and helped maintain Spanish control over the Texas frontier….
Franciscans obeyed the precept of the order’s founder St. Francis of Assisi—to follow the teachings of Jesus Christ in their own lives. The friars dedicated their lives to Humility, Simplicity, Poverty, and Prayer. They owned nothing, served others in their work, and considered themselves as “contemplatives in the marketplace”—prayerful participants in the life of the world….
The Indians of the San Antonio area, the Coahuiltecans, lived in small scattered groups. They took their food from the land and moved with the seasons. They spoke distinct dialects and practiced a religion close to nature. They were a tough and skillful people who made a good living from a harsh land. Threatened by warrior tribes on horseback and weakened by European diseases, many Coahuiltecans accepted the food and refuge offered by the missions….
In the mission once-scattered tribes lived together in a self-sufficient, church-oriented community. Protected and encouraged by the Church they changed from nomadic hunters and gatherers to sedentary farmers. As they became Spanish citizens, many lost their identities as Coahuiltecans….
Spanish soldiers taught the Indians how to defend the mission from Apache and Commanche raiders….
The Franciscans taught the Indians the Catholic faith by a systematic method of instruction. The heart of the method was repetition; the goal of the instruction was understanding. The Church sought converts who understood and observed Christianity and who accepted Spanish culture and language….
The friars carefully controlled the daily life of the mission. On a set schedule the Indians worked, learned vocational skills, and received religious instruction. The goal of this discipline was change—change of the behavior and religious beliefs of these native people….
[The Franciscans viewed the Indians as] Gentiles, Neophytes, and Christians. The friars recognized that conversion would be gradual. They classified as gentiles those Indians who had not yet accepted mission life. Neophytes, those converted to Christianity, lived in the mission and received religious instruction. Christians practiced Christianity and lived independently as Spanish citizens….
Today the missions are elegant reminders of the contribution of Indian and Hispanic peoples to the history of the United States.

A film that introduces visitors to the San Antonio Missions emphasizes that the people who built the missions are still there. The descendants of the Coahuiltecans live all over the area. Mass is still celebrated in the mission churches. However, the missions have had their ups and downs. A historical overview of Mission Concepción from the Texas State Historical Association paints a picture of mission life that is less upbeat than that shown in the interpretive panels. With the passage of time, problems with disease, attacks from the Apaches and Commanches, conflicts with settlers, and the colonial government seizure of mission property, all wore down the mission and drove its people toward poverty. Political instability and wars in the early nineteenth century also took their toll, so that by the early 1850’s the church was being used as a barn by settlers, and was “filled with bats and farm animals”. Its records had been destroyed. But in 1859 Bishop John Odin turned the mission over to the Brothers of the Society of Mary, who began to restore the mission and return its fields to cultivation. Over time Mission Concepción has gradually been restored—its church was rededicated in 2010 following extensive interior and exterior restoration work.
And so it was not until 2003 that the Feast of the Assumption illumination was re-discovered at Mission Concepción by George Dawson, a volunteer docent who happened to be in the church on a sunny day well at around 6:30 pm—after the building was usually closed. He saw the illumination and, as he told the San Antonio Express-News in 2006,
I got goose bumps. I finally knew what was going on in this church. I rushed home and told my wife. On the drive home, I was the only person in the world who knew.
In other words, he thought the illumination was unbelievably cool. This illumination is something that many people find cool, and even inspiring. A local media report on last year’s illumination notes that—

…hundreds crowded into the small church late Wednesday afternoon, spilling into the aisle and edges of the nave, onto the floor of the transept, and all around the chancel and altar and into the larger sanctuary.
This 15th day in August is a special one, the day of the annual solar double illumination when, thanks to the Spanish mission architects and the indigenous laborers who built Concepción, a setting sun in the west casts rays of light through two glass openings. One beam rises slowly toward a sacred space on a painting that hangs above the altar while the other beam pours down through the transept onto the church floor….
And then the hour was at hand, actually 6:25 p.m. by my watch. The light beams settled on their appointed destinations. Last year cloudy skies cut short the occasion, but not this day. Wednesday’s experience did not disappoint.
It was a uniquely San Antonio moment. Gasps of wonder and surprise and a sudden buzz of chatter arose from people in the crammed pews witnessing the double illumination for the first time as one light beam slowly moved onto the visage of Mary and another to the center of the transept.
For many of the worshipers, it was a moment when everything else in life and the city stopped, when science and spirituality married to provide an experience unique to San Antonio.
Part of what makes this phenomenon especially cool at Mission Concepción is the way that the church is constructed. The church has relatively few windows overall, and only four that face in the direction of the front of the church—three in the “choir loft”, and one in the dome. Of the loft windows, only one central, round window stands high enough to throw a beam forward toward the altar without the likelihood of encountering obstructions.

Thus the round loft window and the dome window are what produce the double illumination. The round window illuminates the floor in front of the altar. The dome window illuminates the wall behind the altar. With no other windows for light to come in, the lighting effect is no doubt pretty powerful (I was there on a rainy day in March, so I have not seen the illumination for myself).
It seems likely that the round loft window in particular was designed for the purpose of sending a beam of sunlight into the church to create just this sort of lighting effect. Some Franciscan friar or some Coahuiltecan mason probably said, “hey, this church faces the setting sun—if we put this round window right up top here to let the evening sun beam in during the warmer months, it’ll be really cool…” (or whatever the equivalent of “really cool” is in Spanish or one of the Coahuiltecan languages).
The Mission Concepción church has not been altered much since it was finished in 1755. This illumination phenomenon has been occurring every sunny August 15 evening for over 260 years. It even occurred, and was cool, after it had been forgotten, and the church was full of farm animals!
Cool though it may be, when talking about this sort of thing we ought not to let our imaginations run too far in the direction of “Raiders of the Lost Ark” style Hollywood cool. We ought not to think of some magical instant when a shaft of sunlight blasts through like a laser, lighting things up at some exact moment, and only at that moment. And we ought not to think that this involved some sophisticated astronomical calculations. We don’t need to imagine more than the mason and the friar and “it’ll be really cool”. For example, using the reported time of 6:25 pm from above, and the date of August 15, 2018, I can figure out that at the time of the illumination the sun stood about 3.8 degrees south of due west (its azimuth), and about 35.6 degrees above the horizon (its altitude). At any time in the afternoon or evening when the sun has an azimuth of 3.8 degrees south of west, the round window and the dome window will send beams of light right down the center of the church.

The situation on August 14 or 16 will be little different than what is seen on August 15. And the illumination might be even more dramatic on September 15 at 7:39 pm, when the sun has the same azimuth as August 15, but a much lower altitude, so that the round window’s beam strikes the altar or the wall behind. It may be more dramatic still on September 20 or later (depending on how clear the western horizon is), when the sun will be almost setting and the color of its light is a golden-red.
Moreover, there are equivalent days in the Spring that mirror these days in August and September. And around the solstice the windows will cast their beams more onto the aisle of the church, at around 4:45 pm. As I discussed in a post about the sun and St. Louis Bertrand Church in Louisville, Kentucky (click here for that post), any given window yields a whole season of illuminations. The key is to have a distinct window that produces dramatic lighting, as Mission Concepción does.

Working out such a season of illuminations is a great illustration of what science is. The crowds in Mission Concepción on August 15 evenings suggest that discovering these illuminations—this science—can be good for the life of a church. If you subscribe to this blog and think that your church might have a great illumination, contact me (contact information only appears for readers who are paid-up members of Sacred Space, and logged in as such) via e-mail at christopher.graney@vaticanobservatory.org with the subject line “Church Illumination Calculation”. I would be willing to try to work out the illumination season for your church—if your pastor is interested in the project and would be willing to keep in contact to report whether, and to what extent, the project had a positive impact on the life of the church and on people’s views of science. After all, it’d be really cool!