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Related to UMBRAS: umbral
UMBRASUmbral Missions Blocking Radiating Astronomical Sources
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10.75-6 which contain three mentions of umbra in two lines.
In short, brings together more than 400,000 digitized materials from over 1,000 libraries and archives across the country; and it celebrates the vital efforts of the individuals and institutions that have helped to preserve and make accessible online hundreds of thousands of pieces of African American history and culture, via the Umbra Society of the early 1960s, a group of Black writers and poets who helped create the Black Arts Movement.
More revealing is the facing graph, which shows the model's prediction for how the brightness of the lunar surface varies as a function of the distance from the umbra's edge.