This kind of story makes me want to be a space scientist every time - I am either channeling an astrophysicist or just want to be one in my next life!
According to a press statement, "When Mercury goes in front of the Sun on Wednesday, Nov. 8, a rare event, scientists from Williams College and the University of Arizona will be observing it from vantage points on earthbound mountains and with orbiting spacecraft. Among planets, only Mercury and Venus can go in transit across the face of the Sun, as seen from the Earth, since they are the only planets whose orbits are inside that of Earth's. Transits of Mercury occur a dozen times a century, most recently in 2003. The next won't occur until 2016."
Background includes, "Scientists have already used the 1999 transit of Mercury to unravel a centuries-old mystery known as the black-drop effect. (Their analysis was published in the journal Icarus and in the proceedings of an International Astronomical Union symposium on the transit of Venus.) This blurring of the distinction between a planet's silhouette and the edge of the Sun prevented accurate knowledge of the size of the solar system for hundreds of years. It had been seen at the very rare transits of Venus, which occur in pairs separated by over a century, and often falsely attributed to Venus's atmosphere. Pasachoff and Schneider, on the other hand, by observing and explaining a black-drop effect at a transit of Mercury observed from NASA's TRACE spacecraft, showed that no atmosphere was necessary, since Mercury's atmosphere is negligible and the spacecraft was outside Earth's atmosphere."
See more: NASA Eclipse Page and Transit of Venus Page