SAN ANTONIO -- Members of SALSA or The San Antonio League of Sidewalk Astronomers gathered at McAllister Park Tuesday evening to witness a rare planetary spectacle - the transit of Venus.
The event, which gives curious spectators the opportunity to witness Venus cross the path of the sun last occurred in 2004. However, it won't happen again for another 115 years.
Back in the 18th century, astronomers believed that studying the transit of Venus would provide the answer to one of the most pressing questions of the time - the size of the solar system.
Based on measuring the timing and angles of Venus' crossing, the distance between the Earth and the sun could be calculated.
An interesting anecdote from the 18th century involves astronomer David Rittenhouse's 1769 viewing of Venus' transit. When Venus finally appeared, Rittenhouse fainted, causing him to miss the beginning moments of an historical moment of discovery.
Today, we know the distance from the Earth to the sun is approximately 93 million miles. Admittedly, not far from the measurements of the 18th century astronomers.