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90
Claudius Ptolemy
Ptolemy was the most influential astronomer, geographer, and mathematician of ancient times. He lived in Alexandria, Egypt which was a major center of knowledge of the ancient Mediteranean. He promoted the (geocentric) idea that the Earth was the center of the Universe and that all things revolved around it. This theory prevailed for the next 1400 years. The writings of Ptolemy include names and outlines of 48 constellations that are still in use today. -
Period: 90 to
ancient
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1473
Nicolaus Copernicus
Copernicus wrote a treatment on the solar system that suggested that the Sun was more likely to be in the center than the Earth. It is named "On the Revolutions of the Heavenly Bodies." The idea of a heliocentric or sun-centered system is considered so important to history that it is often referred to as the "Copernican Revolution." -
1546
Tycho Brahe
A Danish nobleman and official Imperial Astronomer to Rudolph II of Prague (before telescopes), he used a "quadrant" to precisely measure the positions of celestial objects, especially Mars. This data would later prove crucial to Kepler in formulating the laws of planetary motion. He observed a supernova and showed that it could not be within our atmosphere. Likewise he showed that comets must be farther away than the Moon. -
1564
Galileo Galilei
Galileo formulated the basic law that all falling bodies fall at the same rate. Notably, he verified his conclusions by carefully designed experiments and measurements. He constructed a refractor telescope with which he viewed craters on the Moon, the phases of Venus, and the rings of Saturn. He discovered four moons revolving around Jupiter. -
1571
Johannes Kepler
Kepler "broke the code" of planetary orbits. After the death of Tycho Brahe he was appointed successor as the Imperial Astronomer and Mathematician. Using Brahe's meticulous notes on the positions of Mars he was able to deduce that the planets orbit around the Sun, but in ellipses, not circles as Copernicus had assumed. Kepler articulated three laws of planetary motion. 1. Planets travel in ellipses with the Sun at one focus of the ellipse. -
Isaac Newton
Listing all of Newton's contributions to science would fill volumes. For the science of astronomy certain areas of work stand out. He designed a new type of reflecting telescope which is now called a "Newtonian" telescope. Most amateur telescopes in use today are Newtonians. He used a prism to show that white light is actually made of colors. His laws of motion and gravity are the basis for understanding Kepler's laws of planetary orbits. -
Edmund Halley
Among his many studies are tides, magnetism, and trade winds. He cataloged 341 southern hemisphere stars and discovered a star cluster in Centaurus. He also made the first complete observation of a transit of Mercury on November 7, 1677. He also invented the diving bell. But his most famous accomplishment is that he worked out a theory of the orbits of comets, concluding that the comet of 1682 (which still bears his name) was periodic, and that it would return in 76 years. -
Charles Messier
Messier was a comet-hunting French astronomer who sought to catalog the location of deepsky objects that could easily be mistaken for comets in small telescopes. His list contains a few more than 100 diffuse objects. The actual number is controversial because of problems with identifying certain objects. M40 may not exist at all, or at best is a dim double star pair. M102 is probably a duplicate entry of M101. -
William Herschel
The discoveries Herschel made are many. He built a 48-inch telescope which was the world's largest for more than 50 years. He discovered what he first thought was a comet, but turned out to be planet Uranus. Eventually he also discovered two moons of Uranus; Titania and Oberon, and two moons of Saturn; Enceladus and Mimas. He determined that our solar system is moving in the direction of Hercules. He went on to catalog about 2500 deep sky objects. -
Henrietta Leavitt
Studying variable stars in the Magellanic Clouds, she discovered that certain variable stars have a cycle that corresponds to their luminosity; the brighter the star, the longer the period. Using this relationship, she was able to determine that the intrinsic brightness of these stars is predictable. By comparing that value to the apparent brightness, the difference can then be used to calculate their distance from Earth. -
Albert Einstein
The contributions that Einstein gave to the astronomical community are so significant that the depth of some them are still being explored today. Some of the areas of major impact concern the nature of light, gravity, and tim -
Edwin Hubble
Before Hubble's big discovery many astronomers thought our Milky Way was the whole Universe. The Andromeda Galaxy was called the Andromeda Nebula. Some had speculated about external "island universes" but Hubble found the proof. Not only did he show that there are giant systems of stars outside the Milky Way (which we now call galaxies), but Hubble's Law explains how the galaxies are receding away from each other.