DUANE
Duane's take
Here's my telling of what the official marker has to say, and friend, this one reaches all the way to the heavens. Let's start with a number so big it'll make your head swim. The solar system.
The whole spread of it. Scientists in the 1700s wanted to measure it — precisely — and they believed the key was locked inside a little black dot drifting slow across the face of the sun. That dot was Venus.
The first recorded observation of Venus crossing the sun goes back to 1639. But it was Sir Edmund Halley — born 1656, died 1742 — who saw the real opportunity. He predicted that if you timed these transits carefully enough, from observation sites scattered around the world, you could use the data to precisely quantify the astronomical unit of distance and, from there, measure the size of the solar system itself.
Now that is a big idea. Here's the catch. Transits of Venus don't exactly come around often.
They arrive in pairs, eight years apart, and then they disappear for roughly 120 years. Scientists got their shot in 1761, and again in 1769, but the timing kept slipping through their fingers — because of something called the black drop effect, where two objects against a bright background appear to blend together right at the critical moment. Like trying to call the exact second two raindrops merge on a windowpane.
So for more than a century, astronomers waited. Prepared. Sharpened their instruments and their patience for the next opportunity.
Now enter a man with a story that has no business being as Texas as it is. Jean-Charles Houzeau. Belgian astronomer, born 1820, died 1888.
Eclectic history is the marker's word, and brother, that is doing some heavy lifting. Houzeau spent time from 1859 to 1861 working as a surveyor out in Uvalde, Texas. He was an abolitionist, and when the Civil War started, he left Texas.
That part of his life was over. But the universe, it turns out, has a long memory. By the late 1870s, Houzeau had returned to Belgium, and he'd risen to become director of the Royal Observatory.
And now here came the next transit of Venus — December 1882 — and it was Houzeau's turn to plan. He organized Belgian teams headed to the western hemisphere. He chose two sites: one in Chile, and one — twenty-two feet to the east, the marker is that specific — in San Antonio, Texas.
San Antonio. The city where, not so many years before, he'd been a surveyor in a state about to tear itself apart. Why San Antonio?
The marker gives you the practical answer: clear skies, favorable weather, good logistics for communication and transportation. A U.S. Naval Observatory team was also out there, observing from grounds at nearby Fort Sam Houston.
The skies over south Texas were open for business. Houzeau brought something else to San Antonio too — a heliometer, a device he had developed specifically for this observation. And on the day of the December 1882 transit, his team captured 124 photographic plates of Venus silhouetted against the sun.
The team in Chile, working under clearer conditions, obtained 606. Now you might think 124 to 606 sounds like losing. But here's where Houzeau's legacy lands.
The Belgian findings equaled those of larger nations. And his decision to bring an international team to San Antonio — to this city on the Texas plain — gave San Antonio a place in astronomical history that no one can take back. A Belgian astronomer who once walked the brush country of Uvalde made sure of it.
What the marker says
The year 1639 marked the first recorded observation of Venus crossing the sun. Sir Edmund Halley (1656-1742) later predicted that using data from such crossings, known as transits, scientists could precisely quantify the astronomical unit of distance and measure the size of the solar system. The transits of Venus predicatably come in pairs, eight years apart, approximately every 120 years. Scientists from around the world traveled to observation sites during the next events, in 1761 and 1769, but timing of the transits was difficult due to the "black drop effect," in which two objects against a bright background appear to blend. For more than a century, astronomers prepared for the next opportunity to record Venus' transit. Jean-Charles Houzeau (1820-1888) was a Belgian astronomer with an eclectic history. From 1859 to 1861, he worked as a surveyor in Uvalde, Texas. An abolitionist, he left Texas at the start of the Civil War. In the late 1870s, he returned to Belgium, where he became director of the Royal Observatory and planned the Belgian teams that would go to the western hemisphere to observe the December 1882 transit of Venus. He chose one site in Chile and one (22 feet east) in San Antonio. Good observations required clear skies, and San Antonio offered the chance of favorable weather, as well as good logistics for communication and transportation. A U.S. Naval Observatory team observed from a site on the grounds of nearby Fort Sam Houston. Using a heliometer, a device he had developed for the observation, Houzeau obtained 124 photographic plates of Venus silhouetted against the sun. Because of clearer conditions, the team in Chile obtained 606. The Belgian findings equaled those of larger nations, and Houzeau's decision to bring an international team to San Antonio provided the city recognition as part of astronomical history. (2005)