Diagram of a Lunar Eclipse

The diagram depicts a celestial sphere. Within it, craggy mountains rise from a turbulent sea, representing the Earth. At the top of the circle is a pitch-black orb, representing the shadow cast by the Earth, while at the bottom, a smaller white circle labeled "Moon" (月) orbits. This visualizes the moment the Moon enters the Earth's shadow.

The point of opposition to the Sun

original: "對月之衝" (duì yuè zhī chōng). In traditional Chinese astronomy, this refers to the point in the sky directly opposite the Sun where the Earth's shadow is cast.

Its size is equal to that of the Sun

Sunlight does not shine there

It is called the Dark Void

Dark Void (Anxu): A classical Chinese astronomical term for the cone of shadow cast by the Earth into space.

When the Dark Void meets the Moon

Then the Moon is eclipsed by it

Lunar Eclipse (Yueshi): Literally "the moon being eaten." This occurs when the Earth passes between the Sun and the Moon, casting its shadow across the lunar surface.

Folio 20, Diagram