While the world was enjoying the rare “super blood wolf moon” earlier this year, a few observant spectators noticed an odd flash of light on the moon’s surface. Planetary scientists have now confirmed that this was a meteorite impact.

A Triple Treat

This was the first known sighting of a meteorite impact on the moon during an eclipse, according to New Scientist. Three astronomical circumstances aligned to make it happen. First, the moon was full, and it was as close to Earth in orbit as it gets, which made it appear to be larger than usual: a supermoon. Secondly, the moon passed into Earth’s shadow for a total lunar eclipse. Then, while the moon appeared dark reddish in the shadow, a space rock crashed into its surface and emitted a bright light as it exploded.

Amateur stargazers around the world were watching the super blood wolf moon by simply looking outside or livestreaming the event online. Some viewers noticed a small flash, and they debated on Reddit whether it had been a meteorite. Meanwhile, scientists in at the University of Huelva in Spain aimed eight telescopes on different parts of the moon to try to observe a meteorite impact during a lunar eclipse and catch it on film for the first time in history.

“I had a feeling, this time will be the time it will happen,” Jose Maria Madiedo told New Scientist.

After the eclipse, University of Huelva’s software automatically pinpointed a flash in imagery recorded by several of their telescopes and helped confirm that it was a meteorite crashing into the lunar surface. According to National Geographic, Madiedo and his team estimated that the meteoroid that people witnessed during the super blood wolf moon was about the size of a football and it left a crater 23 to 33 feet wide. (Wondering about the difference between a meteoroid and a meteorite? Check out this terminology primer from NASA.)

How Often Do Meteorites Come Into Contact With the Moon?

National Geographic reports that similar meteorites hit the moon on a weekly basis. When meteoroids head toward Earth, they usually burn up in our atmosphere. But there is no air on the moon. So, when space debris comes into contact with the moon, some of the energy goes into heat that makes a crater, while a fraction of the energy creates a flash of visible light.

The challenge is that normally the moon is brightly lit, so it’s hard to observe the flash of a meteorite impact (you’re looking for light against a big backdrop of light). An eclipse darkens the moon and makes it easier to catch one of the tiny flashes in action, which is how people were able to witness the meteorite impact during super blood wolf moon.

What the Moon’s Craters Reveal

One of the moon’s most famous characteristics — its cratered surface — provides visible evidence of meteorite impact over many years. Scientists study the moon’s craters to learn about the frequency of meteoroids so that we can anticipate them on Earth and eventually so that NASA can make forecasts to help spacecraft avoid being hit by flying rocks.

The moon’s craters can also help us understand Earth’s history. We’re celestial next-door neighbors, so the meteoroids that fly past the moon should also fly past Earth at the same rate. Interestingly, Earth’s gravity pulls in more meteoroids, but we only know of 180 craters on Earth. The most likely explanation is that Earth’s craters have been covered up by erosion, tectonics and volcanism. There are thousands of visible craters on the moon because it doesn’t have any of these crater erasers, so it is easier to see where meteorites have smashed into the lunar surface.

ScienceNews reports that approximately 290 million years ago, Earth and the moon both saw a sharp increase in impacts. Scientists can estimate the age of a crater because young craters on the moon are surrounded by rocks, which are debris from the impact. The young rocks absorb heat from the sun during the moon’s daytime and radiate it back out at night, which can be observed by NASA. Older craters are surrounded by rocks that have become dust over time, so they don’t glow as brightly as young craters.

On average, 73,000 pounds of meteorites hit Earth every day, according to Space.com, but the exact lunar impact rate is still uncertain because scientists just haven’t observed enough meteorites impacting the moon to make a proper estimate.