David Stevens

Galileo › The Starry Messenger

The moon, 1610

In March 1610 a short book printed at Venice showed the moon as nobody had seen it: a place with mountains and valleys. These are Galileo’s own pictures, from the first edition.

He had been looking at the moon through a telescope he made himself. Then, in January, he turned it on Jupiter, and saw three small stars beside it that turned out to be moons. The Starry Messenger was printed about two months after that first night, and reads like a man in a hurry.

The moon was supposed to be a perfect sphere, made of a different substance from the earth. Galileo saw a ragged line between light and dark, bright points standing out in the shadow, and small hollows whose dark side faced the sun, the way a valley does when the sun comes up behind the hill. The belief these pictures destroyed lay underneath the one about the earth: that the heavens are a different order of thing from the ground.

The title page, Venice, March 1610: Galileo's etching, Sidereus Nuncius, 1610
The title page, Venice, March 1610Sidereus Nuncius: the Starry Messenger. The title promises observations of the moon’s face, countless fixed stars, the Milky Way, and four planets circling Jupiter, which the author has decided to call the Medicean Stars.
A waxing moon: Galileo's etching, Sidereus Nuncius, 1610
A waxing moonLook at the line between light and dark. It is not a smooth curve. Bright points stand out beyond it into the darkness, and shadow bites back into the light.
Near the first quarter: Galileo's etching, Sidereus Nuncius, 1610
Near the first quarterEach small patch has its dark side turned towards the sun. On earth at dawn, a valley is shadowed on the side away from the sunrise. That one detail is the argument.
The waning moon, page ten: Galileo's etching, Sidereus Nuncius, 1610
The waning moon, page tenNear the line between day and night he drew one great round cavity, ringed with shadow, like a valley closed in by mountains. You can see the page’s own Latin beneath it.
Waning, another night: Galileo's etching, Sidereus Nuncius, 1610
Waning, another nightBright specks in the dark part, separate from the lit part, that slowly join up with it. That is what a mountaintop does when sunrise reaches it and then spreads down the slope.
Waning again: Galileo's etching, Sidereus Nuncius, 1610
Waning againThe moon was supposed to be a perfect sphere of a heavenly substance. These pictures made it a place, with terrain, lit at an angle like the ground outside your window.

Images: Sidereus nuncius (Venice, 1610), Rare Book and Special Collections Division, Library of Congress. See the whole book there, or read it in English at Project Gutenberg.

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