A Space Rock Strikes Moon During the Total Lunar Eclipse

The Moon got bonked by a space rock during Sunday's total lunar eclipse. Plus, two supernovae are now visible for telescope users. Take a look!

As if the total lunar eclipse wasn't amazing enough, one binocular observer and more than a dozen people with still and video cameras recorded the split-second flash of a probable meteoroid impact on the Moon at the same time.

The flash appeared west of Mare Humorum (Sea of Moisture) southwest  of the crater Byrgius at 4:41:38 UT (11:41 p.m. EST) only seconds into totality. We don't know how big the object was, though I've seen it described as possibly "the size of a football," but it slammed into the Moon within a few kilometers of latitude 29.47° south, longitude 67.77° west.

Will Young's 4K video of the impact taken from Claiborne Park in southeast Texas shows the impact at multiple frame rates so you can clearly see its evolution from bright to dim over 3–4 frames. He estimated it magnitude at ~7.

Lunar impacts occur all the time. What makes this event so unusual are the circumstances — it happened during a total eclipse watched by millions of people across half the Earth, making it the most widely observed and recorded lunar impact ever. According to David Dunham, who has photographed nine confirmed probable impact flashes, amateur George Varros recorded the only other possible eclipse flash on February 20, 2008. Dunham and Varros, along with other amateur astronomers, now routinely use video cameras to capture impacts, especially during major meteor showers, when the number of meteoroids in the Earth-Moon vicinity skyrockets.

NASA is also keen on studying lunar impact rates. Its Meteoroid Environment Office (MEO), in collaboration with the Marshall Space Flight Center's Space Environments Team, uses twin 14-inch telescopes equipped with video cameras to keep watch for lunar flashes between new and first quarter and again between last quarter and new. Full and gibbous phases are avoided because there's little to no dark portion against which to see impacting meteoroids — except of course when the Moon is in total eclipse! Between 2005 and April 2018 the MEO recorded 435 flashes from meteoroid collisions. Most were bright enough to show in amateur scopes had someone kept a steady watch.

You might be skeptical of claims that the eclipse flasher was the real thing and not a pixel error on a camera chip, glint from an Earth-orbiting satellite, cosmic ray hit, or even a head-on meteor burning up in Earth's atmosphere. We can rule out all four in one fell swoop: multiple observers saw or recorded the flash from widely-separated locations at the same time and at the same exact spot on the Moon. Nothing local about it — the event occurred at the Moon.

According to the MEO, about 33 metric tons (73,000 pounds) of meteoric material pelts Earth every day, nearly all of which  burns up harmlessly in the atmosphere. A steady stream of space grit likewise slams into the Moon, but with little to no atmosphere to resist, it strikes the surface and vaporizes in a flash of light and heat. Speeds of incoming meteoroids range from 20 to more than 72 kilometers per second (45,000–160,000 mph), so even small rocks can pack a wallop. A meteoroid weighing as much as a holiday turkey (~5 kilograms) will excavate a crater over 9 meters across.

Will we be able to spot the impact scar or crater from Earth? Chances are slim as it's probably too small; it doesn't help that it occurred so close to the lunar limb, where everything gets scrunched (foreshortened) because of perspective. But it might be possible for NASA's Lunar Reconnaissance Orbiter to spy the fresh impact with its associated debris apron provided we can pin down the position.

In this video taken by the Griffith Observatory during the total lunar eclipse on January 20, 2019, the flash appears at 3:43:11. It looks just like a flashbulb going off.

Like me you're probably kicking yourself that you weren't staring at the Moon in binoculars or a telescope during the first minutes of totality. When the flash occurred I was either helping someone line up their phone to photograph the red Moon or maybe just in the act of lifting a pair binoculars to my eyes.

If you're interested in hunting for meteoroid flashes yourself, you'll need a moderate-sized telescope, a sensitive black-and-white video camera, and software to record the video to your computer. You'll also want to download a free copy of LunarScan (Windows) to search the video for impact flashes. Most hits appear on just a single video frame for a duration of one-thirtieth of a second or less. The search software eliminates the tedium of watching long videos plus it will pick up the fainter flashes.

Supernovae flashes, too!

But that's not all that's been flashing lately. If you're a supernova freak like I am, there's great news. Two relatively bright exploding stars are now in view in the evening sky. With the Moon departing, hopefully we'll get a look at these incredibly powerful blasts masquerading as pinpoints of light in their host galaxies. Both were discovered by Koichi Itagaki, Japan's most prolific supernova hunter with well over 80 discoveries to his name. Supernova 2018hna appeared in the faint galaxy UGC 7534 on October 22, 2018, and took a long time to rise to its current magnitude of ~14. It's a Type II object involving the catastrophic collapse of a supergiant star at the end of its fuel supply.

Supernova 2019np in NGC 3254 in Leo Minor is a more recent find and easy to spot in 8-inch and larger telescopes at its current magnitude of 13.6. This Type Ia supernova started with a white dwarf star in binary system that accreted enough material from its companion to collapse, heat up, and explosively burn. Type Ia supernovae typically become about 5 billion times brighter than the Sun.

I haven't seen 2019np yet but did view 2018hna a week ago, when it was easily visible at 142× in my 15-inch Dob. The host galaxy is faint — just a misty presence — but the supernova quite plain.