-
276 BCE
Eratosthenes is born
Eratosthenes (276–195 B.C.) used the sun to measure the size of the round Earth. His measurement of 24,660 miles (39,690 kilometers) was only 211 miles (340 km) off the true measurement. -
1473
Nicholaus Copernicus is born
In 16th century Poland, astronomer Nicolaus Copernicus (1473–1543) proposed a model of the solar system that involved the Earth revolving around the sun. The model wasn't completely correct, as astronomers of the time struggled with the backwards path Mars sometimes took, but it eventually changed the way many scientists viewed the solar system. -
Feb 15, 1564
Galileo is born
Galileo was born in Pisa (then part of the Duchy of Florence), Italy, on 15 February 1564,[15] the first of six children of Vincenzo Galilei, a lutenist, composer, and music theorist, and Giulia Ammannati, who had married in 1562. -
Dec 27, 1571
Kepler is born
Kepler was born on 27 December, 1571, in the Free Imperial City of Weil der Stadt (now part of the Stuttgart Region in the German state of Baden-Württemberg, 30 km west of Stuttgart's center). His grandfather, Sebald Kepler, had been Lord Mayor of the city. -
Supernova Discussion, Galileo
Tycho Brahe and others had observed the supernova of 1572. Ottavio Brenzoni's letter of 15 January 1605 to Galileo brought the 1572 supernova and the less bright nova of 1601 to Galileo's notice. Galileo observed and discussed Kepler's Supernova in 1604. Since these new stars displayed no detectable diurnal parallax, Galileo concluded that they were distant stars, and, therefore, disproved the Aristotelian belief in the immutability of the heavens. -
Kepler's First Law
After approximately 40 failed attempts, in late 1604 Kepler at last hit upon the idea of an ellipse,[54] which he had previously assumed to be too simple a solution for earlier astronomers to have overlooked.[55] Finding that an elliptical orbit fit the Mars data, Kepler immediately concluded that all planets move in ellipses, with the Sun at one focus—his first law of planetary motion. Because he employed no calculating assistants, he did not extend the mathematical analysis beyond Mars. -
Giovanni Cassini is born
Italian astronomer Giovanni Cassini (1625–1712) measured how long it took the planets Jupiter and Mars to rotate. He also discovered four moons of Saturn and the gap in the planet's rings. When NASA launched a satellite to orbit Saturn and its moons in 1997, it was fittingly dubbed Cassini. -
Christiaan Huygens is born
Dutch scientist Christiaan Huygens (1629–1695) proposed the earliest theory about the nature of light, a phenomenon that puzzled scientists for hundreds of years. His improvements on the telescope allowed him to make the first observations of Saturn's rings and to discover its moon, Titan. -
Isaac Newton is born
25 December 1642, Isaac Newton was born "an hour or two after midnight",[11] at Woolsthorpe Manor in Woolsthorpe-by-Colsterworth, a hamlet in the county of Lincolnshire. His father, also named Isaac Newton, had died three months before. (Wikipedia, October 2021) -
Edmond Halley is born
Edmond Halley (1656–1742) was the British scientist who reviewed historical comet sightings and proposed that the comet that had appeared in 1456, 1531, 1607, and 1682 were all the same, and would return in 1758. Although he died before its return, he was proven correct, and the comet was named in his honor. -
Newton's Celestial Mechanics
In 1679, Newton returned to his work on celestial mechanics by considering gravitation and its effect on the orbits of planets with reference to Kepler's laws of planetary motion. This followed stimulation by a brief exchange of letters in 1679–80 with Hooke, who had been appointed to manage the Royal Society's correspondence, and who opened a correspondence intended to elicit contributions from Newton to Royal Society transactions.[55] -
Publishing of Newton's Principia
The Principia was published on 5 July 1687 with encouragement and financial help from Edmond Halley. In this work, Newton stated the three universal laws of motion. -
Charles Messier is born
French astronomer Charles Messier (1730–1817) composed a database of objects known at the time as "nebulae," which included 103 objects at its final publication, though additional objects were added based on his personal notes. Many of these objects are often listed with their catalog name, such as the Andromeda Galaxy, known as M31. Messier also discovered 13 comets over the course of his lifetime. -
William Herschel
British astronomer William Herschel (1738–1822) cataloged over 2,500 deep sky objects. He also discovered Uranus and its two brightest moons, two of Saturn's moons, and the Martian ice caps. William trained his sister, Caroline Herschel (1750–1848), in astronomy, and she became the first woman to discover a comet, identifying several over the course of her lifetime.