science & techThe Public Domain Review1680s · The Hague, Netherlands

Christiaan Huygens reasoned about alien life in 1698 using the new astronomy

the gist

In the late 1680s the Dutch astronomer Christiaan Huygens, ill and isolated in The Hague after losing his post in Paris, began writing Cosmotheoros, a book speculating about life on other planets. Unlike earlier work based on philosophy or religion, it drew on recent scientific knowledge. He asked his brother to publish it only after his death, which came in 1698. Huygens had discovered Saturn's moon Titan in 1655 and had worked out that Saturn was surrounded by a ring, so he had good grounds to picture what the sky looked like from another world. He wondered about the effects that Saturn's ring would have on those who lived beneath it. The book was quickly translated into Dutch and English, where it appeared as The Celestial Worlds Discover'd.

so what

Cosmotheoros is one of the earliest attempts to reason about extraterrestrial life with real astronomy, anticipating debates that remain active today. It shows how the telescope turned speculation about other worlds into a question that could be argued from evidence.

fun fact

Christiaan Huygens discovered Saturn's moon Titan in 1655.

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