Asteroid 4 Vesta, the brightest asteroid visible from Earth, and one of the larger, at about 530 km wide, was first spotted on March 29th 1807 by Heinrich Wilhelm Olbers. It is named after the Roman goddess of the home and hearth, who always had a fire burning in her temples as a reminder. Vesta is the second most massive asteroid (after Ceres, which had been discovered the year before) but is only the third biggest by volume (Pallas, also discovered by Olbers, five years earlier, takes second place).
Vesta was visited recently (July 2011) by NASA’s Dawn spacecraft, which took the above image (actually it’s a collection of many images stuck together). Observations show it to be an oblate spheroid, but irregularities in shape and the low mass mean it doesn’t qualify as a dwarf planet under the current naming rules.
2002 – Launch of the Reuvan Ramaty High Energy Solar Spectroscopic Imager (HESSI, or RHESSI) to study solar flares.