The Nebula Awards annually recognize the best works of science fiction or fantasy published in the United States. The awards are organized and awarded by the Science Fiction and Fantasy Writers of America (SFWA), a nonprofit association of professional science fiction and fantasy writers. They were first given in 1966 at a ceremony created for the awards, and are given in four categories for different lengths of literary works. A fifth category for film and television episode scripts was given 1974–78 and 2000–09, and a sixth category for game writing was begun in 2018. The rules governing the Nebula Awards have changed several times during the awards’ history, most recently in 2010. The SFWA Nebula Conference, at which the awards are announced and presented, is held each spring in the United States. Locations vary from year to year.
The astronomers found that larger craters, which excavated pits much deeper into the Moon's surface, only increased porosity in the underlying crust. This indicates that these deeper layers have not reached a steady state in porosity, and are not as fractured as the megaregolith.
For those craters smaller than 30 kilometers in diameter, he discovered impacts both increased and decreased porosity in the upper layer of the lunar crust.
Conventionalized images of the Man in the Moon seen in Western art usually display a simple "face" in the full Moon, or a human profile in the crescent Moon, that correspond to real topological features on the lunar surface.