Nicole-Reine Lepaute

She is an astronomer, April:

Nicole-Reine Lepaute

1723-1788

Nicole-Reine Lepaute worked with another astronomer Jerome Lalande and mathematician Alexis Clairaut to compute the return date of Comet Halley. This required many calculations to determine the daily position of the comet on its orbit, taking into account the perturbations due to the giant planets Jupiter and Saturn. Her calculations made it possible to determine the dates of the next passage of the most famous comet. In 1762 she performed some calculations about the 1764 solar eclipse. She published several astronomical papers and articles, one of which reported all observations made of the Venus transit in 1761.

She was born in the Luxembourg palace in Paris where her father was working for Queen Isabel of Orleans.

An asteroid and a lunar crater have been named after her.

On the calendar there's also an artist's impression of her pointing out a comet, and a black-and-white portrait.

Her wikipedia entry doesn't have much detail; there's more about her life and work at the University of St Andrews site.