In the 18th century the world was focused on Venus. Expeditions were launched in pursuit of exact measurements of Venus as it passed between Earth and the Sun. By viewing its journey and location on the Sun's surface, scientists hoped to make a massive leap in scientific knowledge. With a little help from math, Scientist in Residence Regina G. Barber recounts how humanity came closer to understanding our cosmic address — and relative distances to other planets — in the solar system. You can follow Regina on Twitter @ScienceRegina. Email Short Wave at ShortWave@NPR.org.