Caught on camera: A small rock hit the moon | Science News for Students

Caught on camera: A small rock hit the moon

The impact was spotted during January’s lunar eclipse
Mar 6, 2019 — 6:45 am EST
an image of the moon and where the impact happened

During a lunar eclipse on January 21, amateur astronomers caught lucky views of an object roughly the size of a basketball smacking into the moon and producing a bright flash of light (inset).

Fritz Pichardo/Dominican Astronomical Society

On January 21, something smacked into the moon, creating a flash of light. Things hit the moon all the time. But this time one thing was different. Thousands of people were watching. The impact took place during a total lunar eclipse. And there are pictures to prove it.

Astronomers are using the pictures to gauge the size of the rock that hit the moon. Jorge Zuluaga is one of them. He works at the University of Antioquia in Medellín, Colombia. He and his colleagues gathered images from amateur astronomers in Colombia and the Dominican Republic. Those two countries are in South America and the Caribbean. There was also a video livestreamed on from an observatory in Morocco.

With these data, Zuluaga’s team calculated characteristics of the impact. For instance, it likely released the energy equivalent of about half a ton of TNT. That means the rock that hit the moon was somewhere between the size of a softball and a basketball. It probably had the mass of a few cans of paint — 7 to 40 kilograms (15.5 to 88 pounds). The astronomers also calculate that the object smacked into the moon at 13.8 kilometers per second. That’s almost 31,000 miles per hour.

Their results appear in a paper posted January 28 at

Here’s how Zuluaga remembers the story. He couldn’t see the eclipse because it was cloudy. But the next day, he saw reports on Twitter. Some observers had reported a bright flash. People assumed it was a meteorite strike. Zuluaga contacted amateur astronomers he had worked with before and found several who had photographed the impact.

The researchers then estimated that the impact probably left a crater on the moon between 5 and 10 meters wide (16 to 32 feet). That scar could be spotted with a current or future lunar orbiter.

That the impact happened during a lunar eclipse is important, Zuluaga says. It supports the idea that the moon is hit with meteorites almost constantly. Scientists estimate something hits the moon once an hour, on average.

The event also highlights the potential for discovery when amateur and professional astronomers work together. “A lunar eclipse is not as interesting for professionals as for amateur astronomers,” Zuluaga says. “But when you have these kinds of surprises, it is a blessing to have amateurs as friends.”

Power Words

(more about Power Words)

amateur     One who engages in a pursuit as a pastime, not as a profession.

arXiv     A website that posts research papers — often before they are formally published — in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance and statistics. Anyone can read a posted paper at no charge.

astronomy     The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.

average     (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

Caribbean     The name of a sea that runs from the Atlantic Ocean in the East to Mexico and Central American nations in the West, and from the southern coasts of Cuba, the Dominican Republic and Puerto Rico down to the northern coasts of Venezuela and Brazil. The term is also used to refer to the culture of nations that border on or are islands in the sea.

colleague     Someone who works with another; a co-worker or team member.

crater     A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.

current     A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.

eclipse     This occurs when two celestial bodies line up in space so that one totally or partially obscures the other. In a solar eclipse, the sun, moon and Earth line up in that order. The moon casts its shadow on the Earth. From Earth, it looks like the moon is blocking out the sun. In a lunar eclipse, the three bodies line up in a different order — sun, Earth, moon — and the Earth casts its shadow on the moon, turning the moon a deep red.

gauge     A device to measure the size or volume of something. For instance, tide gauges track the ever-changing height of coastal water levels throughout the day. Or any system or event that can be used to estimate the size or magnitude of something else. (v. to gauge) The act of measuring or estimating the size of something.

lunar     Of or relating to Earth’s moon.

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

meteorite     A lump of rock or metal from space that passes through Earth’s atmosphere and collides with the ground.

moon     The natural satellite of any planet.

observatory     (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes.

orbiter     A spacecraft designed to go into orbit, especially one not intended to land.

Twitter     An online social network that allows users to post messages containing no more than 280 characters (until November 2017, the limit had been just 140 characters).


Journal:​ ​​ J.I. Zuluaga et al. Location, orbit and energy of a meteoroid impacting the moon during the Lunar Eclipse of January 21, 2019. arXiv:1901:09573. Posted online January 28, 2019.