Banneker, a mostly self-educated man in mathematics and astronomy, is best known for building America’s first clock—a wooden device that struck hourly. Using his rich understanding of trigonometry and astronomy, he accurately predicted a solar eclipse in 1789.

Banneker was also a passionate civil rights advocate. In 1791, he famously penned a letter to the secretary of state Thomas Jefferson asking for his help in improving conditions for Africans living in the United States, which highly impressed Jefferson and convinced many that blacks were intellectually equal to whites.

He died at age 74 on October 9, 1806.

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