The Black Moon is the "egg" of Lilith, a transport vessel created by the First Ancestral Race to send Lilith to Earth. It collided violently into Earth 4 billion years ago in the event dubbed "First Impact", and came to rest deep beneath the Earth's surface in the region that would eventually become Hakone, Japan. Buried under the surface, the Black Moon formed a spherical underground cavity of gigantic size termed a "GeoFront", around which Tokyo-3 and NERV Headquarters were eventually built. According to production sketches, the Black Moon is 13.75 km in diameter.
In Episode 26', the Black Moon emerged out of the ground and into Earth's atmosphere where Lilith collected all the souls of mankind into it for the purpose of Instrumentality. Later, after Instrumentality was halted, the Black Moon exploded, releasing all of the souls held within it.
Rebuild of Evangelion
The Black Moon appears in Evangelion 3.0: You Can (Not) Redo, emerging from the ground during the awakening of Evangelion 13. It has been heavily modified into a shape resembling a Holy Grail. After the impact caused by Evangelion 13 is stopped, the Black Moon fails to completely rise out of the ground, and remains visible as a large spherical 'hill'. It can be seen once more in the post-credits trailer for Evangelion: Final
- Black Moon is term from astrology to describe the lunar apogee, when the moon is furthest away from the Earth and hence at it's most dim in our skies.
- In 1846, Frederic Petit, a French astronomer, claimed to have found a second moon in an elliptical orbit around the Earth. This was called the "Dark Moon" or "Black Moon" because it was nearly invisible. In 1918, Walter Gornold, an astrologer, dubbed the second moon "Lilith". No real scientific claims of the existence of this moon have ever been proven, but it is sometimes used in astrology, where it is closely tied to the myth of Lilith.
- It is not possible to determine what material the Black Moon is made of. It has a physical structure and is not simply an underground cavity, as seen in The End of Evangelion. Also, despite having the roof excavated and covered with an armored roof as the surface of the city of Tokyo-3 (later completely destroyed), the black moon appears to be an intact sphere when it rises out of Earth's surface (Although the destroyed portion is only a small fraction of its total surface area, the damage should still be visible).