Griffith Observatory in Los Angeles also recorded the impact during its livestream of the eclipse.
A second flash was seen a minute after the first by some observers, Anthony Cook, an astronomical observer at Griffith, said.
“It was in the brightest part of the moon’s image,” Cook said of the second suspected strike, “and there might not be enough contrast for the flash to be visible in our video.”
Cook thought it could just have been the camera’s random electronic noise. Then astronomers and citizen scientists started to share their detection of the flash on reddit and Twitter.
The only explanation was that something slammed into the lunar surface and obliterated itself.
The moon is a multibillion-year-old library of impact events, with fresh collisions still taking place frequently.
Capturing a lunar impact on video is rare enough, but capturing this event – a collision during a total lunar eclipse – was unique.
“I have not heard of anyone seeing an impact like this during a lunar eclipse before,” said Sara Russell, a professor of planetary sciences at the Natural History Museum in London.
Russell said that flashes could be seen from Earth only when the lunar surface was in shadow, which is normally a few days before and after the new moon. A luminous full moon is anathema to such detections, but a total lunar eclipse, painting the moon in darkness, changed that.
Madiedo said that monitoring of lunar impacts was generally conducted five days before and after a new moon, when flashes can be easily observed.
To take advantage of the three-plus-hour eclipse, he set up four extra telescopes in addition to the four he operates at the observatory in Seville.
“I did not want to miss any potential impact event,” he said in an email.
“I could not sleep for almost two days, setting up and testing the extra instruments, and performing the observation during the night of January 21,” he wrote. “I was really exhausted when the eclipse was over.”
Then computer software alerted him to the impact.
“I jumped out of the chair I was sitting on. I am really happy, because I think that the effort was rewarded,” he said.
Moon monitoring can help scientists better predict the rate of impacts, not just on the moon but on Earth, Madiedo noted.
He helps run the Moon Impacts Detection and Analysis System, or MIDAS , in Spain.