A Chronological History of Astronomy

Ancient Astronomy

• 4500 BC: In Brittany (currently France), the Stones of Carnac were constructed. This area, similar to Stonehenge, is made up of stones that stood upright in a pattern. Some think they were signposts, but many believe that they were aligned with the sun or moon in a special way.
• 3500 BC: The Pentre Ifan Dolmen Tomb was constructed in Wales. This structure, which is a burial place composed of stone balanced on each other, was also built so that it aligned with certain stars or the sun and moon.
• 3000 BC: Stonehenge was constructed in England. Perhaps, the most famous stone structure on Earth, it’s believed that these stones were placed into this specific structure to track both the regular movement of the moon and the occurrences of lunar eclipses.
• 2000 BC: The first solar-lunar calendars were put into use in Egypt and Mesopotamia. Known as Solunar calendars, these calendars consist of 12 lunar months. The calendar is not linked to the seasons and drifts by 11 days every year, coming back to its original dates every 33 Islamic years.
• 280 BC: Aristarchus of Samos, a Greek, first proposes that the earth – and all other plants – revolved around the sun, not the Earth as it had been believed for years. However, his ideas were rejected and not revived until nearly 1800 years later.
• 130 BC: Hipparchus of Greece manages to develop the first accurate star map and catalogue that has over 850 of the universe’s brightest stars. Hipparchus, the father of trigonometry, also developed the system of epicycles where everything in the universe revolved in perfect circles, fitting Aristotle’s earth-centered universe theories.

Medieval Astronomy

• 900 AD: An Arab astronomer named al-Battani calculates that the length of a year is in fact 365 days, 5 hours, 48 minutes, and 24 seconds. Before that, it had been accepted as 365 days, 6 hours. This more precise measurement served to show that the Earth’s distance from the sun was varied and put a chink in the idea that planets moved in perfectly circular orbits.
• 964 AD: Another Arab astronomer named al-Sufi publishes that he has discovered a number of objects in the sky that are hazy and fuzzy. These are, in fact, star clusters and galaxies that astronomers are only just able to fully understand. Amongst them was the Andromeda Galaxy.
• 1040 AD: Astronomer al-Biruni develops a method of science that uses triangulation to allow him to measure the Earth’s radius to a value that would not be improved for another 500 years.
• 1120 AD: In Cairo, Egypt a large observatory begins being constructed. It’s believed to be possibly the first observatory in Medieval Islam but it is never completed. The observatory’s patron is convicted of communicating with Saturn and executed. In 1125, the observatory was destroyed.
• 1200 AD: Many Greek and Arab books are translated into Latin. Aristotle’s ideas about cosmology are adopted by the Catholic Church and any dissention in later years would be treated as heresy, something that would doom many astronomers to come.

Renaissance Era Astronomy

• 1420 AD: Ulugh Beg, a Persian astronomer, has a 3-story observatory built. This observatory is able to produce star charts that catalogued over 1,000 stars. As a result of his three decades of findings, he is believed to be the most important observational astronomer in the 15^th century.
• 1543 AD: Nicholas Copernicus publishes a book suggesting that the Sun is actually the center of our universe with the other planets revolving around it on an axis. The idea is met by harsh criticism and his book is even banned by the Catholic Church.
• 1572 AD: Danish astronomer Tycho Brahe notices a new star appearing in the sky and disappearing two years later. He also observes that comets are actually moving in space, not crystal spheres holding the planets, proving that not all motion in space is circular. Brahe measures the year to an accuracy of a single second, making it easier to introduce the Gregorian calendar in 1582.
• 1596 AD: Astronomer David Fabricius observes that a star called Omicron Ceti varied its brightness over several months. This was important because it placed yet another dent in the theory that the heavens were unchanging as was the norm at the time.
• 1600 AD: An Italian astronomer named Giordano Bruno begins teaching that the universe is actually infinite. He also teaches that the Earth moves around the sun and that the stars are other suns with planets of their own. Bruno was burned at the stake for heresy in 1600 in Rome.

Modern Astronomy

• 1610 AD: Galileo Galilei, famed astronomer and mathematician, begins observing the heavens with a newly invented telescope. He discovers stars that have never been seen before and sunspots on the sun, indicating that it rotates on an axis. He also sees Venus complete a cycle of phases and makes a series of other discoveries that basically invalided all the previously supported theories about the solar system.
• 1620 AD: German mathematician John Keplar begins using Brahe’s observations about Mars to show that planets do actually move in elliptical orbits, finally causing astronomers to relinquish the theory that they move in perfect circles. He also proves that the closer a planet is to the sun, the faster it moves.
• 1656 AD: An astronomer from the Netherlands, Christian Huygens, discovers a moon around Saturn. He also discovers a ring around the planet, something never before observed. He declares that, since they have discovered six planets and six moons, the solar system is complete.
• 1666 AD: Sir Isaac Newton begins working on his book Principia. In it, he clearly explained how the movements of all the planets depended on gravity and proved it with his experiments. His Laws of Motion were published in this book. He also explained the connection of the tides to the moon and proved that the laws that governed the solar system were the same laws that governed the earth.
• 1676 AD: Olaus Roemer observes the planet Jupiter and all of its moons. He notices that the eclipses of Jupiter’s moons was occurring later than astronomers expected and noted that this had to be because the distance between the planets caused a delay in the time it took for the light from the eclipses to reach the earth. He calculates the speed of light to 75% accuracy, incredible for the time.

Astronomy of the 20th Century

• 1906 AD: A Dutch astronomer named Jacobus Kapteyn repeats William Herschel’s analysis of the stars and discovers something interesting: the order in the motions of the stars. He proves that stars do not move about the galaxy at random. He also tries to calculate the size of the galaxy but the figure is less than 60% of the real size.
• 1912 AD: A woman named Henrietta Leavitt forms what is called the Period-Luminosity law. She discovers that a particular star type known as Cepheid stars have regular luminosity periods and they are easily distinguished in star clusters. These clusters are all the same distance from the earth and she was able to discover a link between a star’s period and luminosity. The longer its period, the brighter it was. This is useful for measuring distance between objects in the universe.
• 1913 AD: Walter Adams manages to come up with a way of measuring a star’s luminosity based on what spectrum it belongs to. A scale was invented: blue stars are the most luminous, then yellow, then red.
• 1916 AD: Albert Einstein presents the world with his Theory of Relativity, which was a theory about the structure of space-time. It says that the laws of physics are the same for everything and that the speed of light in a vacuum is exactly the same as well.
• 1923 AD: The Hubble telescope observes and proves that there are planets beyond the Milky Way Galaxy, reinforcing the idea that there are many other galaxies in the entire universe.
• 1969 AD: Neil Armstrong and Buzz Aldrin, two Americans, land on the moon as part of the Apollo 11 mission, a culmination of years of attempts to get living humans to the surface of the moon.
• 1976 AD: The US probes that were part of the Viking mission land on Mars and begins conducting experiments. They monitored the weather and returned high resolution photos. They also collected some evidence that water may have once been present on the planet.
• 1990 AD: The Hubble Space Telescope is put into orbit, where it remains, by the space shuttle Discover. The Hubble is still sending back truly amazing pictures to the earth and it has even become part of a multi-country project.
• 2000 AD: More evidence that supports theories that liquid water can be found on Mars is discovered. A surveyor takes images of recent channels which could have been formed by water as opposed to older channels which could have been developed during the planet’s formation. Experiments are still ongoing.