The largest impact on the moon ever seen by human beings apparently just happened last September.

Researchers from Spain's University of Huelva and also Institute of Astrophysics of Andalusia report a space rock approximately the size of a small automobile slammed into the lunar surface Sep. 11 and produced an extended flash that lasted about 8 seconds and was brighter than the North Star.

The scientists' account of the event has been published in the Monthly Notices of the London-based Royal Astronomical Society.

"I was immediately aware that I was witnessing an extraordinary event," lead researcher José María Madiedo of the University of Huelva said in a press release.

Madiedo detected the impact by using two telescopes used by the Moon Impact Detection and Analysis System project, which was developed by Madiedo and fellow scientist José Luis Ortiz, also from the university.

Such impacts, Madiedo explained, are mainly caused by comet fragments and asteroids orbiting around the sun, otherwise known as meteoroids.

While the earth's atmosphere protects it from most meteoroids on a collision course with the Blue Planet, the moon doesn't have one, which means even small fragments can hit its surface and leave a crater.

Typically, the relatively small projectiles are traveling at tens of thousands of miles an hour when they impact. The resulting explosions get hot enough to melt rock and vaporize the meteoroids instantly.

"That is why we do not use the word meteorite when referring to these collisions, because that term implies the presence of fragments," Ortiz explained.

As well, the collisions usually cause a momentary rise in temperature that in turn produces a glow that is visible with telescopes from the earth for about a fraction of a second on average.

The report by Madiedo and Ortiz suggests the new crater could measure up to an estimated 40 meters, or, roughly 70 feet, in diameter.

The meteoroid itself, they explained, looks to have weighed about four hundred kilograms and sported a diameter between 0.6 and 1.4 meters.

The energy released during the impact was equivalent to the ignition of about 15 tons of TNT.