Giordano Bruno is a small lunar impact crater whose eponym is the Italian philosopher Giordano Bruno. It is located on the far side of the Moon, just beyond the northeastern limb. At this location it lies in an area that can be viewed during a favorable librations, although at such times the area is viewed from the side and not much detail can be seen. It lies between the Harkhebi crater to the northwest and Szilard crater to the southeast.

When viewed from orbit, Giordano Bruno is at the center of a symmetrical ray system of ejecta that has a higher albedo than the surrounding surface. The ray material extends for over 150 kilometers and has not been significantly darkened by space erosion. Some of the ejecta appears to extend as far away as the Boss crater, over 300 km to the northwest. The outer rim of the crater is especially bright, compared to its surroundings. To all appearances this is a young formation that was created in the relatively recent past, geologically-speaking.

Were it not for the fact that it was possibly formed less than 1000 years ago, it would just be an obscure crater.

Formation

Shortly after sunset on June 18, 1178, five monks from Canterbury reported seeing what they described as two horns of light on the shaded part of the moon. In 1976 the geologist Jack B. Hartung proposed that this passage described the formation of the Giordano Bruno crater.

Modern theories predict that there would be a plume of molten matter rising up from the surface of the moon, which is consistent with the monks' description. In addition, the location they recorded fits in well with Bruno's location. Additional evidence of Bruno's youth is its spectacular ray system: because micrometeorites constantly rain down, they kick up enough dust to quickly (in geological terms) erode a ray system. So there is probably enough circumstantial evidence to hold that Giordano Bruno was formed during human history.

However, the question of Bruno's age is not that simple. The impact creating the 22 km wide crater would have kicked up enough debris to make a meteor storm on Earth with roughly 50,000 meteors per hour, for up to a week. There is no way the entire population of the planet could possibly have missed what might be considered the greatest fireworks show in history. This is such a major objection that few astronomers still believe Bruno formed then.

All this raises the question of what the monks saw. An alternative theory holds that the monks just happened to be in the right place at the right time to see an exploding meteor coming at them and aligned with the Moon. Only a small area in Britain would have the perfect geometry to make it look like it was on the Moon.