Location, orbit, and energy of a meteoroid impacting the Moon during the lunar eclipse of 2019 January 21

Document Type


Publication Date



Department of Physics


During lunar eclipse of 2019 January 21, a meteoroid impacted the Moon producing a visible light flash. The impact was witnessed by casual observers offering an opportunity to study the phenomenon from multiple geographical locations. We use images and videos collected by observers in seven countries to estimate the location, impact parameters (speed and incoming direction), and energy of the meteoroid. Using parallax, we achieve determining the impact location at lat.−29.43+0.30−0.21⁠, lon.−67.89+0.07−0.09⁠, and geocentric distance as 356 553 km. After devising and applying a photometric procedure for measuring flash standard magnitudes in multiple RGB images having different exposure times, we found that the flash, had an average G-magnitude 〈G〉 = 6.7 ± 0.3. We use gravitational ray tracing (GRT) to estimate the orbital properties and likely radiant of the impactor. We find that the meteoroid impacted the moon with a speed of 14+7−6 km s−1 (70 per cent C.L.) and at a shallow angle, θ < 38.2 deg. Assuming a normal error for our estimated flash brightness, educated priors for the luminous efficiency and object density, and using the GRT-computed probability distributions of impact speed and incoming directions, we calculate posterior probability distributions for the kinetic energy (median Kmed = 0.8 kton), body mass (Mmed = 27 kg) and diameter (dmed = 29 cm), and crater size (Dmed = 9 m). If our assumptions are correct, the crater left by the impact could be detectable by prospecting lunar probes. These results arose from a timely collaboration between professional and amateur astronomers that highlight the potential importance of citizen science in astronomy.

Publication Title

Monthly Notices of the Royal Astronomical Society