June 7, 2020

The Early Astronomers: A Brief History of Astronomy.

Ye ‘ole telescope…(Photo by Author).

(Editorís note: The following is an essay wrote by yours truly in the quest for a science teaching degree. Now that said degree has come to fruition, our writing can be immortalized forever in a re-vamped blog format).

Astronomy is one of manís earliest pursuits for knowledge. Once we began living in organized communities and brute survival and safety wasnít a constant and overriding concern, we began to look up and ponder our place in the cosmos and contemplate the workings of the heavens above us.

Early primitive astronomy is a tale interwoven with religious cosmology and astrology. The very yearning to discover that we are connected with the universe stems from this innate longing. But the modern science of astronomy demonstrates that we are all connected with space and astronomical events, not in the superficial way that our early superstitious beliefs would suggest, but on the most fundamental and physical of levels.

The ancient Greeks were some of the first true astronomers that took an earnest look at the skies and systematically recorded what they saw. For example, Hipparchus accurately calculated the distance to the Moon and knew the Earth was round based on the appearance of the cross-section of the Earthís shadow as seen during a lunar eclipse. He also devised the system on by which stellar brightness or magnitudes of celestial objects could be measured. Similarly, Eratosthenes calculated the circumference of the Earth by observing the difference in the angle of the noon day Sun on the summer solstice at two locations; his native Alexandria in Egypt and what we now know of as the Tropic of Cancer due south of his location. Aristarchus of Samos even proposed that not only was the Earth round, but it in fact circled the Sun. Two key figures to ancient Greek knowledge were Aristotle and Ptolemy. Both championed an Earth-centered, geocentric universe, with the Sun, Moon, planets, and celestial firmament revolving about us on complex epicycles. Ptolemy also gave us some of the first and most complete star charts of the era. While both men were outstanding scientists, the churchís later unquestioning acceptance of their doctrine would hold sway over scientific thinking for over a millennium. In addition to geocentrism, Aristotle held that the Moon was a smooth sphere and the heavens were unchanging. He also taught that nature could be understood by rationalization and conceptualization, rather than observation and experimentation. How different would our world be today had the works of Aristarchus instead survived and been adopted?

A true revolution in astronomy would have to wait until the publication of Nicholas Copernicusís On the Revolutions of the Heavenly Spheres in 1543. Copernicus noted that the complex and cumbersome system of geocentric epicycles could be largely done away with if the Sun was simply placed at the center of the solar system and the Moon orbited the Earth, which in turn was simply another planet. This also beautifully and simply explained retrograde motion as the appearance of the backwards movement of one planet as it over took another in its orbit.† Many thinking and educated men of the time knew the reality of heliocentrism to be correct, but the idea flew in the face of church doctrine. At the time of the Protestant Reformation, the Catholic Church could scarcely face an idea that disagreed with biblical dogma. The works of Nicholas Copernicus would remain on the churchís Index of forbidden works until 1758.

In the meantime, Danish astronomer Tycho Brahe was making some of the most accurate measurements known of planetary positions. A flamboyant character, Brahe was also one of the first astronomers to enjoy a royal stipend, complete with his own observatory and private island on which to carry out his observations.

But true credit deductive interpretation of Braheís observations would go to Braheís contemporary Johannes Kepler. Like Brahe, Kepler also subsidized a living by casting royal horoscopes, but his true passion was astronomy. Keplerís life work was a dogged pursuit of an idea he had early on: why are there five classical geometric solids and exactly five planets? Today, of course, we know that the idea was a mere coincidence of Kepler’s time. Keplerís work, coupled with Braheís observations instead solved a much more fundamental issue of heliocentrism. Namely that the planets, especially Mars, didnít appear exactly in the sky where they should be. Kepler realized that the problem could be solved if the planets traveled not in neat circles, but ellipses. This led to the establishment of his famous three laws of planetary motion; 1. That all planets move in ellipses; 2. The motions of these planets sweep out a period that is equal to the area of the orbit; And 3.The orbital period squared is directly proportional to the cube of the orbitís semi-major axis.

The stage was now set for the true birth of modern astronomy. One evening in early 1610, Galileo turned his newly constructed telescope skyward. Galileo did not invent the telescope, but he was the first to use it to systematically observe the heavens and record what he saw. He noted craters, mountains, and ďseasĒ or maria on the Moon, in direct contradiction of Aristotle. He saw four tiny moons that followed Jupiter and changed position night to night. He noted that the Milky Way itself could be further resolved into stars too faint to be seen with the naked eye. And most significantly, he noticed that the planet Venus underwent phase changes like the Moon, further support for the Copernican heliocentric theory.

A final culmination of renaissance astronomy and physics was to express itself through the works of Sir Isaac Newton. Newton invented the reflecting telescope, a device that was simpler to construct than Galileoís tiny refractors and yielded larger apertures and were largely free of the defects that plagued refracting lenses. Newton also explained how light could be broken down into a spectrum, which ultimately led to the science of spectroscopy, which enables astronomers to deduce the chemical composition of distant objects. But his most critical contributions were expressed in his landmark work entitled Mathematical Principles of Natural Philosophy, the cornerstone of which are his three laws of motion: 1. An object set in motion will stay in motion until an external force is applied to it; 2. Force is equal to mass times acceleration, or F=ma; and 3. For every action there is an equal and opposite reaction. Deceptively simple, these three rules explain how Keplerís laws work and predict the position of orbiting objects such as our own Moon about the Earth. In 1846 Urban Le Verrier used Newtonian physics to accurately predict the position of an unknown body tugging at Uranus. This triumph led to the discovery of Neptune, the first planet that was found by scientific deduction. Even today, when we send a spacecraft to other worlds, scientists rely on Newtonian physics to put them in the right place at the right time.

In conclusion, modern astronomy has been a series of incremental steps throughout history. This knowledge has been hard won, as ideas of the universe as we would like it to be are slowly replaced by the reality and theories of the cosmos as it truly is. But far from simply demoting us to inhabiting a tiny world orbiting an insignificant star, astronomy has also shown us what a precious and unique place the Earth truly is, as well as how the very elements of carbon, nitrogen and oxygen forged in stars can assemble themselves, given billions of years, and eventually form life capable of pondering its own existence and place in the universe.


  1. Gerard says:

    Very interesting. Galileo was a revolutionary astronomer. However its telescope was designed by the Dutch Hans Lippershey, who tried to sell the design to his Government, about one year before. The Dutch government refused it and, then, the telescope’s drawings arrived in the Galileo’s hands.

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