At a convention in Paris in 1887, the world’s best astronomers hatched an ambitious plan. Harnessing the emerging technology of glass-plate cameras, they would photograph and map every star in the night sky, plotting each star’s position in an enormous catalog. This massive undertaking would require the participation of 20 observatories across six continents, each of which was assigned to chart a corner of the cosmos.

There are probably plenty of cases to be made for various “most badass”contributions to the Carte du Ciel, as the multi-decade (and still incomplete) project came to be known. This one has to do with nuns.

Shortly after the initiative was launched, in something of a symbolic gesture of support for scientific research, Pope Leo XIII permitted the Vatican Observatory to help the project along. (Yes, such an observatory exists to this day; various iterations have been operating since the late 18th century.) A series of astronomer-monks were put in charge of the Vatican’s obligations to the Carte du Ciel, but the labor largely involved rote number-crunching and tedious data transfer. Not every high-profile brother-scientist was up to the task.

That’s why in 1909, the archbishop in charge of the observatory wrote to the nearby Sisters of the Holy Child Mary community, reportedly asking for “two sisters with normal vision, patience and a predisposition for methodical and mechanical work.”

Jesuit Father Sabino Maffeo, the present-day archivist and assistant to the director of the Vatican Observatory, told the Catholic News Service that the sisters’ general council was not thrilled “about wasting two nuns on a job that had nothing to do with charity.” But the superior general was apparently “used to seeing God’s will in every request,” and allowed two sisters to go help. The Catholic News Service reports on the instrumental scientific work performed by these women:

Work for the sisters began in 1910, but soon required a third and later a fourth nun to join the team. Two would sit in front of a microscope mounted on an inclined plane with a light shining under the plate-glass photograph of one section of the night sky. The plates were overlaid with numbered grids and the sisters would measure and read out loud each star’s location on two axes and another would register the coordinates in a ledger. They would also check enlarged versions of the images on paper. … From 1910 to 1921, the nuns surveyed the brightness and positions of 481,215 stars off of hundreds of glass plates.

The “alacrity and diligence” of Sisters Emilia Ponzoni, Regina Colombo, Concetta Finardi, and Luigia Panceri was given special praise in the Vatican’s final product, a 10-volume “astrographic catalog” published in sections between 1900 and 1928. How’s that for a spiritual mission accomplished?