Venus passes between the Earth and the sun—known as the Transit of Venus—just about twice per century. The last passage of our lifetime takes place June 5 (the next won't happen until 2117). Astronomers have watched this journey for centuries, but over time, technology has created new ways to experience the age-old event.
PAST In 1874 and 1882, an exciting new technology called photography documented the transit. A few early shutterbugs contributed to science: Their best shots were used to measure our solar system's size, and to increase our understanding of planets.
PRESENT Astronomers Without Borders offers a mobile app for amateur astronomers to document the transit (with the help of a telescope). For novice stargazers, the organization's web app lets anyone viewing the transit discuss it on Twitter and Flickr.
FUTURE Michael Zeiler, a GIS professional at Esri, which contributed to the development of the web app, expects big changes: "Humankind will have begun colonization of the solar system, and future settlers on Mars will witness the transit of Earth in 2084."