Well into the 20th century, the first sentence of many articles describing lunar rays stated that their origins were enigmatic. This was due to our poor understanding about these bright, filamentary streaks radiating from many young lunar craters. That perception began to change with Ralph Baldwin's transformative 1949 book, The Face of the Moon. Baldwin was the first to convincingly make the case for the impact origin of lunar craters by asteroids and comets (rather than volcanic eruptions), with the rays being material ejected during crater formation. A decade later, legendary lunar scientist Eugene Shoemaker published the first ballistic analysis of lunar impacts and the resulting emplacement of ray-forming ejected rocks. Since then, Apollo 12 astronauts collected samples of a ray from Copernicus, and scientists have even studied rays on other worlds. It's safe to say that rays are no longer completely mysterious, though some of their features aren't fully understood.
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