The first African American astronomer was Benjamin Banneker. He was born in 1731 and was largely self-taught in astronomy and mathematics. There is an extensive biography of him on biography.com titled, “Benjamin Banneker.”
While I couldn’t find an answer on the first African American woman astronomer, I did find that Dr. Beth Brown, Ph.D was the first African American woman to earn a doctorate in astronomy from the University of Michigan is this article, “Black Women Making Their Mark in Space & Science.”
For more on prominent African American astronomers, check out this webpage from the University of Buffalo.