Sometimes a flash in the night is actually an asteroid slamming into the moon.
Because such impacts offer valuable information about Earth's own barrage of space rocks, scientists have established programs that look for the brief bright flashes on the moon that represent lunar impacts. A new such telescope recently began operations, confirming observations of another telescope's 100th impact flash detection.
Having multiple eyes on the moon is valuable for scientists because other phenomena, like satellites passing overhead, can produce similar flashes in the data. But two observatories at different locations won't simultaneously see the same satellite: if both catch the same lunar flash at the same time, it's definitely real data.
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The European Space Agency's Near-Earth Object Lunar Impacts and Optical Transients (NELIOTA) project, based at Kryoneri Observatory in Greece, does just this type of work. So far, the project has spent nearly 150 hours staring at the moon and observed 102 flashes. The instrument can also provide data that lets scientists estimate the temperature of the impact.
The milestone 100th observation came on March 1. And as scientists looked back over NELIOTA's data, they realized that a newcomer to the lunar impact patrol, the Sharjah Lunar Impact Observatory in the United Arab Emirates, had spotted the same flash. Scientists were able to compare images taken by the two observatories and line up lunar features, in addition to checking the timestamps of the flashes.
The double observation marks an important milestone for lunar impact surveillance efforts. "Cross detections like this are very useful as they rule out the possibility of a slow, bright satellite being misidentified as an impact flash," Detlef Koschny, co-manager of the Planetary Defense Office of the European Space Agency, said in a statement.
"While NELIOTA has other, less-direct means of excluding such events, we're excited to have more eyes on the moon, helping us to understand the rocky road our planet travels on," Koschny said. The Earth and moon are close enough — on the scale of the solar system — that both bodies should be hit by more or less the same hail of space rocks.
The flashes these observatories track come from just the sort of space rocks that regularly hit Earth without scientists being able to spot them: rocks that weigh less than 3.5 ounces (100 grams) and are less than 2 inches (5 centimeters) across, according to the statement. Rocks that small don't make it very far into Earth's thick atmosphere before burning away.
But the moon has no such atmosphere, so the same size rock can hit the surface — pretty flashy.
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Good question and answer!
If we look at the typical speed of an asteroid that hit Earth, it drops down to something like 20 km/s, which is Earth orbital speed. In essence Earth, and I expect Moon, acts like giant fly swatters with an overlay of own speed of impactor in relation to Sun as well as Earth gravity as bolide says.
Given that NELIOTA looked 149 hours before seeing its 100th flash (or about once every hour for 5+ cm impactors), I expect to see the impacts distributed over the whole surface in relation to the orbital plane http://www.esa.int/Safety_Security/100th_lunar_asteroid_collision_confirmed_by_second_telescope ]. That would tend to cluster the impacts towards the equator (perpendicular vs horizontal surface projection), as well as screen the emission from the impact with a corresponding angle, as well as becoming hidden behind any topography. I expect a sharp drop off in seen impacts towards the poles - a combined impact and emission sin^2 angle effect in a 1 D slice and it is "2D" emission cones so radiation dispersal in the angled projection becomes even worse I think (haven't worked the problem), as well as Moon having lots of crater walls et cetera that starts to come in the way - and that is what we seem to see here.