1631 - French scientist Pierre Gassendi is the first to see a transit of Mercury using a telescope.
1639 - Giovanni Zupus, an Italian astronomer, uses a telescope to observe the phases of Mercury for the first time.
1841 - Johann Franz Encke estimates the mass of Mercury by calculating the effect of the planet's gravitational pull on the comet Encke.
1881 - Another Italian astronomer, Giovanni Schiaparelli, observes Mercury and sees dark streaks on the planet. Because they don't seem to move, he concludes that one side of Mercury always faces the Sun. This was not proved wrong until 1965.