Astronomy Timeline

1665				Giovanni Cassini discovers Great Red Spot of Jupiter. Although its size and darkness have changed with time, the Great Red Spot has been continuously present since the time of Cassini's discovery. P 256. F 12.6, 12.12.
1666				Robert Hooke shows that a central force leads to orbital motion. Hooke used a pendulum to demonstrate to the members of the Royal Society that in order to stay in orbit, the planets must be continually pulled toward the Sun. P 74. F 5.4.
1665-7				Newton discovers law of universal gravitation. When Cambridge University was closed by the plague, Newton spent most of the next two years at his family farm. During this period he made fundamental discoveries in optics, discovered the law of universal gravitation, and invented differential and integral calculus. P 75.
1667				G. Montanari notices brightness variations of Algol. Montanari saw that Algol occasionally dropped to a third of its normal brightness. Later, the drops in brightness were found to be caused by eclipses. P 484. F 21.7
1668				James Gregory makes the first realistic estimate of the distances of the stars. Gregory assumed that the other stars were just as bright as the Sun and then calculated how distant they had to be to match their apparent brightnesses. P 362.
1678				Christian Huygens proposes that light consists of waves. Huygens's ideas were disputed by Newton, who proposed that light was mae up of a stream of particles. P 95. F 6.2.
1682				Edmund Halley predicts return of Comet Halley. Halley noted that comets with similar orbits had appeared in 1456, 1531, 1607, and 1682. He proposed that these were all the same comet and that it would return in 1758 or 1759 - which it did. Pp 342-343. F 15.17.
1686				Newton publishes "Principia". Newton's monumental work described his discoveries about gravity, motion and the orbits of the planets. Pp 75-85. F 5.5, 5.6, 5.7, 5.8, 5.9, 5.11, 5.12.
1718				Edmund Halley discovers stars move through space. Halley found that the positions of stars change with time. He explained the changes in position as due to the individual motions of stars through space. Pp 363-364. F 16.2.
1729				James Bradley discovers the aberration of starlight. Bradley found that the positions of all the stars shift back and forth as part of an annual cycle caused by the motion of the Earth about the Sun. P 144. F 8.1.
1781				William Herschel discovers Uranus. While measuring the directions and brightnesses of stars, Herschel found a fuzzy spot that moved among the stars. This was Uranus, the first planet that was not known to the ancients. P 280.
1781				Charles Messier prepares list of nebulae. Like other comet hunters, Messier often mistook nebulae for comets. He compiled a list of 103 nebulae as an aid to other comet hunters. This was the first list of nebulae. P 534.
1783				John Goodricke discovers eclipses of Algol. Goodricke found that the brightness declines of Algol occur at regular intervals. He proposed that the brightness changes are due to eclipses of Algol by its binary companion. P 484. F 21.7.
1783				William Herschel discovers speed and direction of Sun's motion. Herschel analyzed the motions of seven bright stars and showed that part of their motions was due to the motion of the Sun through space. P 364. F 16.3.
1785				William Herschel uses star counts to map Milky Way. Herschel assumed that the galaxy extended farther in directions in which he could see more stars. He found the galaxy to be flattened with the Sun near the middle. Pp 513-514. F 22.22, 22.23.
1790				Pierre Simon Laplace proposes stars can produce black holes. Laplace proposed that if a star is so compact that its escape velocity exceeds the speed of light, then not even light can escape from the star. Pp 468-469.
1801				Giuseppe Piazzi discovers Ceres. Piazzi discovered Ceres, the first known asteroid, on January 1, 1801, the first day of the 19th century. P 336.
1801				William Herschel shows many double stars are binaries. Herschel found that for many pairs of stars, the orientation of the two stars changes with time. The changes are a result of orbital motion. P 480. F 21.1
1802				William Wolleston sees dark lines in solar spectrum. Wollaston passed sunlight through a prism and noticed that there were numerous dark bands and lines in the spectrum. P 369.
1803				Meteorite shower at l'Aigle convinces scientists that meteorites have an extraterrestrial origin. A careful investigation of the shower by Edouard Biot convinced most skeptics that meteorites really do fall from the sky. P 333.
1833				Denison Olmstead discovers shower meteors come from a common point in the sky. Olmstead realized that the meteors seem to diverge from a point in the sky because they originate in a swarm of meteoroids moving on parallel paths through space. P 331. F 15.2.
1835				Gaspar de Coriolis discovers Coriolis effect. The Coriolis effect, the apparent deflection of moving bodies due to Earth's rotation, explained many atmospheric circulation patterns. Pp 146-147, F 8.6, 8.7.
1837				h Carinae brightens to become second brightest star. h Carinae is normally too faint to be seen, but between 1837 and 1860 it was the brightest star in the sky. P 450. F 19.26.
1838				Friedrich Bessel, Wilhelm Struve, Thomas Henderson measure the distances of stars. Bessel, Struve, and Henderson, working independently, almost simultaneously measured the parallaxes, and hence the distances, of nearby stars. These were the first measurements, rather than estimates, of stellar distances. Pp 362-363. F 16.1.
1842				Christian Johann Doppler describes the Doppler effect. Doppler discovered that the wavelength and frequency of a wave change if the source of the wave moves toward or away from the observer. P 94. F 6.6.