It hasn't happened in ten years... a rare passage of the planet Mercury in front of the sun called a "Mercury Transit."
It won't be visible with the naked eye but can be seen from 7 a.m. until 2 p.m. this afternoon through a telescope with a proper sun filter.
Planet Mercury Transits only happen in the months of November and May, and the next time it happens in the month of May won't be until the year 2049.
Sherzer Hall Observatory will be open to the public Monday, May 9th from 7 A.M. to 2 P.M., weather permitting.
NASA has more information about the transit.