What the moon is; why the sun looks larger at sunset
The moon shines by reflected light like a mirror; luminous bodies seem to grow with distance and through denser air.
Among solar and lunar diagrams Leonardo asks what the moon is and answers that it is not luminous of itself but receives light like a mirror or water. He holds that every luminous body appears to grow the farther off it is, so the sun and moon look larger near the horizon; the dark patches on the moon he takes to be land amid its waters, just as our world would look to men living on the moon. A second diagram explains the enlarged sunset sun by the longer, denser column of air the eye looks through, since a body seen through a curved medium appears larger than it is. A short note and a side view of water running over an uneven bed close the page.
On this page
What the moon is: a mirror for the sun's light
The moon is not luminous of itself but is well suited to receive light, like a mirror, water, or another shining body. It grows larger in the east and west, as do the sun and the other planets, because every luminous body grows larger the farther away it goes.
The dark stains on the moon are land among its waters
If you were where the moon is, the sun would reflect in as much of the sea as it illuminates by day, and the land among the waters would look like the dark stains on the moon, which appear to men on earth exactly as our world would to men living on the moon.
Why the sun appears larger at sunset
Why does the sun appear greater at sunset than at midday, when it is nearer? Every body seen through a curved medium appears to be of greater form than it is.
Two positions of the sun over an observer (a, c, b, d)
A diagram of the earth shows the sun directly over the observer b and again on his horizon, both positions joined to the earth's centre; a third body d is set above the second sun, and a corner is labelled c.
Water at deep river bottoms stays colder in summer
If the water flowing over the great river bottoms does not enter with a blow, it will not reach the bottom; so the water at the bottom changes little and remains colder in summer and hotter in winter than the rest.