Astronomers Through History
The first astronomers lived in ancient Mesopotamia, Egypt, China, Greece, and India. They simply followed the movement of celestial objects across the sky as could be seen by the naked eye. The invention of the telescope furthered astronomers’ reach into space. Now astronomers have a myriad of tools to look beyond anything that could have been previously imagined. Here is a list of some of the most important astronomers and their contributions.
Galilieo’s Sketch of the Moon
- Claudius Ptolemy (CE 90-168) was a Roman citizen who lived in Egypt. His name is important to know more for what he got wrong in astronomy. Though other Greek writers previously had devised the heliocentric, or sun-centered, model of the solar system, Ptolemy devised the geocentric, or Earth-centered, model of the solar system which was not widely and popularly disproved for centuries. He also wrote a treatise on astrology.
- Polish astronomer Nicolaus Copernicus (CE 1473-1543) published On the Revolution of the Celestial Spheres shortly before his death. The book challenged the idea of the Earth-centered, Ptolemic model of the solar system and placed the Sun back at the center of the solar system. He described the apparent motion of the Sun in the sky as the result of the Earth’s rotation. His work started what is referred to as the Copernican Revolution, a sudden explosion of new ideas in the various fields of science throughout the renaissance.
- Building on the work of Copernicus, Johannes Kepler (AD 1571-1630) described the laws of planetary motion in his works Astronomia nova and Harmonices Mundi. While previous models featured circular orbits, Kepler’s works described elliptical orbits. His work was used by Isaac Newton to describe the laws of universal gravitation. Newton also made improvements to the reflecting telescope.
- Galileo Galilei (AD 1564-1642) is perhaps the most famous astronomer. He further legitimized the heliocentric model of the solar system, made improvements to the refracting telescope, discovered several moons of Jupiter, observed sunspots and the phases of Venus, and discovered craters and mountains on the moon. He also observed that the Milky Way was a large number of stars closely packed together to give a cloudy appearance. For his views espousing heliocentricism, the Catholic Church placed Galileo under house arrest until he died.
- Edmond Halley (AD 1656-1742) used his theory of cometary orbits to correctly predict the appearance of the comet which would be named Halley’s comet. This is the best known and most visible short-period comet. It appears every 75 to 76 years and was last seen in 1986.
- Edwin Hubble (AD 1889-1953) demonstrated the vastness of the universe by observing other galaxies outside of the Milky Way. He also noted the degree of the redshift of these galaxies. The redshift refers to the Doppler effect and shows that galaxies are speeding away from each other, and the further away the galaxy the faster it is moving away from us. This became known as Hubble’s Law, and it helped the establish the expansion of the universe.
Source: Famous Astronomers, James Pickering, Dodd, Mead Publishing, 1968.
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