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Two lunar flashes are reported and fully analyzed, with one of them fulfilling every criterion preconized in the literature for the characterization of an impact, including confirmation by two simultaneous observations. It happened at 07:13:46 UT on 14 December 2017, at the selenographic coordinates of 9.79° (±0.06°)N and 45.42 (±0.07°)E. The peak magnitudes in the R and V bands vary from 6.3 to 7.9 and from 7.4 to 9.0, respectively, depending on the observatory, as the cameras' exposure times were considerably different. The impactor mass is estimated to be between 1.6 and 2.0 kg, with a diameter of 10 to 11 cm, having produced a crater of 8.4 to 8.9 m in diameter. Results for the second flash are also presented and discussed, although the confirmation of an impact was not possible due to a pause in the recordings at one of the sites. The observations took place as part of an inaugural observing campaign in Brazil for lunar impact flash (LIF) detection conceived by the Brazilian Meteor Observation Network (BRAMON) and were carried out by two teams located in different states in the Northeast Region of Brazil, about 353 km apart from each other, at a time when the Moon was crossing the densest part of the Geminid meteoroid stream in 2017. The observing setups included 0.13 m and 0.2 m telescopes, both equipped with sensitive cameras. The Maceió setup probably delivered the finest definition ever reported in the literature for lunar impact monitoring, resulting in high-accuracy positioning. This will certainly aid in finding the associated crater from orbiter images, which will substantiate another work, aimed at performing a comparative analysis between the results from our photometry and the data retrieved by the LRO images. These observations were also very likely the first and the only one so far made by a normal framerate camera and a long-exposure camera simultaneously. The associated benefits are commented on. The source of the impactors is also discussed. In view of the successful results of this experience, national observing campaigns of this kind will be given continuation. [ABSTRACT FROM AUTHOR]

An impact of a meteoroid on the lunar surface at speeds exceeding several kilometers per second generates a light flash generally less than 0.1 s in duration. We made a simple spectral video camera for observing the lunar impact flashes and monitored the waxing crescent Moon's non-sunlit surface from Oct. 2016 to May 2017. We detected ten flash candidates though there was no report of simultaneous detections by other observers. We obtained low-dispersion spectra in visible wavelengths for nine of them. Six of them show spectra similar to those of the flashes observed during the Geminids meteor activity in Dec. 2018 by the same camera. The spectra are continuous and red. Blackbody spectra fitted to them show temperatures around 3000 K. On the other hand, three of them show continuous blue spectra. Blackbody spectra fitted to them show temperatures of more than 6000 K. Specular reflection of sunlight by space debris might lead to these flashes. However, the impact of a low-density meteoroid not against the fine lunar regolith but solid lunar rocks could cause blue flashes. In this paper, we give full details of the camera and the analytical procedures of the videos. We also discuss recommendations for future spectral observations. [ABSTRACT FROM AUTHOR]

Abstract: The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18h28m27s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are and , and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of . Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles. [Copyright &y& Elsevier]

Lunar impact flashes have been observed at collisions of meteoroids against the non-sunlit lunar surface at speeds exceeding 10 ​km ​s−1. We detected 13 flash candidates between 6.2 and 9.9 in R-magnitude on December 15, 2018 during the Geminids meteor activity. Two or three observatories confirmed eleven of them. We obtained their spectra in the wavelength range between 400 and 870 ​nm. They are continuous and red, with best-fitted single blackbody spectra indicating the temperatures of about 2000–4000 ​K. The temperatures for a few successive movie frames at 16 ​ms or 25 ​ms intervals decrease with time. Incandescent ejecta, consisting of melt droplets or dust, and the radiant floor of an impact crater could be the source of these flashes, except for the initial stages. At the beginning of some flashes, we found an excess of fluxes at short wavelengths of less than about 600 ​nm. The composites of two blackbody spectra may fit the spectra better where their temperatures are about 2000 K and 6000 ​K. The contribution of a high-temperature vapor plume, generated at the very beginnings of the impact phenomena, could be important. Image 1 • Visible and near-infrared spectra of lunar impact flashes were obtained for the first time. • The spectra of the lunar flashes due to the impacts of the Geminids' meteoroids are continuous and red. • Best-fitted single blackbody spectra show flash temperatures of about 2000–4000 ​K. • The composite of two blackbody spectra, where its high-temperature component would represent radiation from an impact-generated vapor plume, could explain the observed spectra better in the initial stage of the flashes. [ABSTRACT FROM AUTHOR]

When a meteoroid impacts on the Moon, a brief flash phenomenon—called a "lunar impact flash"—can be observed by ground-based telescopes. The statistics of these events can efficiently determine the meteoroid size-frequency distribution in cis-lunar space. The luminous efficiency—that is, the ratio of luminous energy emitted to the impactor's kinetic energy—is the most important parameter for precise meteoroid-size estimation. Thus, it is necessary to understand the impact-flash mechanism and determine the luminous efficiency under various conditions. We have, therefore, performed hypervelocity-impact experiments at JAXA, and measured the relation between luminous efficiency and ambient pressure at various vacuum levels. Based on a high-speed spectroscopy, we find that the flash consists of blackbody radiation from hot ejecta and blackbody radiation from a vapor cloud together with emission lines and molecular bands. Spectrum analysis reveals that the initial luminous efficiency within the first few μs does depend on the vacuum level, whereas the luminous efficiency over several ms does not depend on the vacuum level. • Hypervelocity Impact flash consists of blackbody radiation from ejecta and vapor cloud, emission lines, and molecular bands. • Luminous efficiency within a few μs is affected by vacuum level due to ablation between impact fragments and ambient atmosphere. • Luminous efficiency over several ms does not depend on vacuum level. • For lunar impact flash study, we can perform rough vacuum level (e.g., several tens of Pa) and frequent impact experiments. [ABSTRACT FROM AUTHOR]