The light of the moon: is the moon a mirror of the earth?
Diagrams of sun, moon and earth, with an argument on how the moon and earth reflect light.
Turned on its side, the sheet carries small diagrams of the sun, moon and earth in various positions and of the moon's orbit around the earth, labelled with letters and the words sun and moon. The main note argues that if the moon is a mirror of our earth, then at the full moon the earth would appear half dark and half illuminated. Leonardo reports an adversary's view that the earth, being surrounded by water, reflects moonlight only through that water, while its own unpolished surface stays dark, so that our seas shine back into the moon carrying the darkness of the islands they surround.
On this page
Sun, moon and earth in various positions
At the centre the sun and earth are drawn in several positions, together with the sun and full moon and the moon's orbit around the earth. The small figures are labelled with letters and with the words for sun and moon.
If the moon mirrors the earth, the earth looks half dark
If the moon is a mirror of our earth, then when it is at the fifteenth day (full) the earth would be half dark and half illuminated, or perhaps more than half dark. Of dark bodies one cannot make out the shape of the things lying within their boundaries.
Why the earth's water shines back into the moon
The adversary holds that moonlight illuminates the part of the earth it sees, but since the earth is surrounded by water, only the water mirrors that light. The land, not being clear and polished like water, sends no likeness of itself and stays dark, so our water shines in the moon carrying the darkness of the islands it surrounds.