Hevelius's book on comets. Title page of Cometographia (1668), by the Polish astronomer Johannes Hevelius. The artwork shows three astronomers representing three theories about comets. From left, the theories are: Aristotle's sublunar theory (that comets orbit between the Moon and the Earth); Hevelius's theory that comets originate from Jupiter or Saturn and follow parabolic paths around the Sun; and Kepler's theory that comets move in a straight line. On the roof of the building (right), telescopes and sextants are being used to observe a comet (top left).

Demonstration at Cologne Cathedral of the Earth's rotation.

Hevelius's book on comets. Title page of Cometographia (1668), by the Polish astronomer Johannes Hevelius. The artwork shows three astronomers representing three theories about comets. From left, the theories are: Aristotle's sublunar theory (that comets orbit between the Moon and the Earth); Hevelius's theory that comets originate from Jupiter or Saturn and follow parabolic paths around the Sun; and Kepler's theory that comets move in a straight line. On the roof of the building (right), telescopes and sextants are being used to observe a comet (top left).

Constellation of Leo.

Demonstration at Cologne Cathedral of the Earth's rotation.

Demonstration at Cologne Cathedral of the Earth's rotation.

Apparatus of Johannes Hevelius (about 1640), used for studying the sun. Hevelius, a German astronomer, was also noted for his map of the moon and his star catalogue. His work was typical of the astronomical revolution of the 17th century.

Anonymous watercolor depicting the comet of 1680 over the Low Countries.

Herschel's galactic model, 1784. This is one of several visualizations drawn by the British astronomer William Herschel (1738-1822). Working with his sister, Caroline, Herschel plotted the position of many of the Milky Way's stars, and used this data to construct models of the Milky Way galaxy, as seen from the outside. The crosses represent stars, while the letters refer to specific stars and constellations. The model is not particularly accurate, but does show the central band of stars that is the central plane of our galaxy. A version of this model was published in Account of Some Observations Tending to Investigate the Construction of the Heavens (Philosophical Transactions of the Royal Society of London, volume 74, 1784).

A rendering of the reflecting telescope used by William Herschel, the discoverer of the planet Uranus. Astronomical Society of the Pacific.

Anonymous watercolor depicting the comet of 1680 over the Low Countries.

Anonymous watercolor depicting the comet of 1680 over the Low Countries.

Herschel's galactic model, 1784. This is one of several visualizations drawn by the British astronomer William Herschel (1738-1822). Working with his sister, Caroline, Herschel plotted the position of many of the Milky Way's stars, and used this data to construct models of the Milky Way galaxy, as seen from the outside. The crosses represent stars, while the letters refer to specific stars and constellations. The model is not particularly accurate, but does show the central band of stars that is the central plane of our galaxy. A version of this model was published in Account of Some Observations Tending to Investigate the Construction of the Heavens (Philosophical Transactions of the Royal Society of London, volume 74, 1784).

Herschel's galactic model, 1784. This is one of several visualizations drawn by the British astronomer William Herschel (1738-1822). Working with his sister, Caroline, Herschel plotted the position of many of the Milky Way's stars, and used this data to construct models of the Milky Way galaxy, as seen from the outside. The crosses represent stars, while the letters refer to specific stars and constellations. The model is not particularly accurate, but does show the central band of stars that is the central plane of our galaxy. A version of this model was published in Account of Some Observations Tending to Investigate the Construction of the Heavens (Philosophical Transactions of the Royal Society of London, volume 74, 1784).

Herschel's galactic model, 1784. This is one of several visualizations drawn by the British astronomer William Herschel (1738-1822). Working with his sister, Caroline, Herschel plotted the position of many of the Milky Way's stars, and used this data to construct models of the Milky Way galaxy, as seen from the outside. The crosses represent stars, while the letters refer to specific stars and constellations. The model is not particularly accurate, but does show the central band of stars that is the central plane of our galaxy. A version of this model was published in Account of Some Observations Tending to Investigate the Construction of the Heavens (Philosophical Transactions of the Royal Society of London, volume 74, 1784).

A rendering of the reflecting telescope used by William Herschel, the discoverer of the planet Uranus. Astronomical Society of the Pacific.

A rendering of the reflecting telescope used by William Herschel, the discoverer of the planet Uranus. Astronomical Society of the Pacific.

A rendering of the reflecting telescope used by William Herschel, the discoverer of the planet Uranus. Astronomical Society of the Pacific.

An illustration ridiculing the practice of astrology.

An illustration ridiculing the practice of astrology.