On June 5, 2012, a rare event occurred - the planet Venus traversed the disk of the Sun, an event called a Venus transit. Because of the geometry of the orbits of Venus and the Earth, Venus transits happen in pairs separated by 8 years, with each pair separated by more than one hundred years! The last transit of Venus was on June 8, 2004. But the next pair of Venus transits will not happen in our lifetime! Venus will not cross the face of the Sun again, as viewed from Earth, until December 11, 2117. Images of this truly historical event were captured by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory satellite, and the X-Ray Telescope (XRT) aboard the Hinode satellite.
Transits of Venus are beautiful, but they are also scientifically useful. In the late 1700's, astronomers all over the world carefully measured the position of Venus as it crossed the Sun's disk. From these measurements, they were able to accurately measure the distance from the Earth to the Sun. Telescopes have improved significantly since then, of course, and modern day astronomers used the Venus transit in 2004 to study the properties of the atmosphere of Venus.
AIA was developed with the help of scientists and engineers from the Harvard-Smithsonian Center for Astrophysics in concert with the lead institution, the Lockheed Martin Solar and Astrophysics Laboratory. XRT was built at the Smithsonian Astrophysical Observatory in Cambridge, MA in partnership with NASA and Japan Aerospace Exploration Agency (JAXA).