Annie Jump Cannon was an American astronomer. Graduated with a degree in physics and astromy in 1884, she developed her skills in the new art of photography.
In 1896, Cannon became a member of "Pickering's Women", a group of women hired by Harvard College Observatory to complete the Henry Draper Catalogue, with the goal of mapping and defining every star in the sky to a photographic magnitude of about 9. Thanks to her visual memory, her patience and her work organisation, she became an expert in stellar classification.
From 1911 to 1914, she examined photographic plates and identified spectral type of each star with magnitude 9 or less. She classified then about 5000 stars a month.
Based on Williamina Fleming's classification, she developed stellar classification which is the basis of Harvard classification and which is still used today.

I hope this serie of hanjies can be a collective serie. So don't hesitate to publish a "Women behind ? (3)", 4, 5 and so on... You just have to mention it in the comments.

Difficulty : ****

Tested, logical.
Not require any specific method, only single-line logic.
Good "blackenage".