If you see a flashing light while looking at the moon, it might not be an optical illusion but an meteoroid impact; from 100 Explosions on the Moon (NASA):
Over the past two and a half years, NASA astronomers have observed the Moon flashing at them not just once but one hundred times.
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“Even when no meteor shower is active, we still see flashes,” says Cooke.
Below is an impact near crater Gauss on January 4, 2008 (NASA):
…explosions don’t require oxygen or combustion. Meteoroids hit the moon with tremendous kinetic energy, traveling 30,000 mph or faster. “At that speed, even a pebble can blast a crater several feet wide. The impact heats up rocks and soil on the lunar surface hot enough to glow like molten lava–hence the flash.”
ceo