A Timeline of Astronomy's Origins
Astronomy is regarded as the oldest branch of science. At first, ancient civilizations would interpret the skies in a religious manner rather than a scientific one; this is now known as astrology. Some of the earliest records of astronomical observation date back to 1600 B.C. when the Babylonians tracked the position of celestial bodies and frequency of certain phenomena such as days and nights. This timeline documents the greatest discoveries of astronomy, shaping astral studies as we know it today.
500 B.C. The Ancient Greeks gathered astronomical records from the past. They utilized these observations to navigate and create or solve questions about the skies above. Thales of Miletus, a greek mathematician, was able to use mathematics and astronomical data to calculate when an eclipse would occur.
Geocentric Model of the Universe
270 B.C. Aristarchus of Samos proposed a heliocentric model of the universe, which proposed the sun was the center of the universe. At the time, the heliocentric model was unfavorable as Newtonian physics had not yet been developed.
Thales of Miletus
330 B.C. Heraclides Ponticus created the geocentric model which showed Earth as the center of the universe, which was widely accepted for a long period of time until the heliocentric model became more popular.
Aristarchus' Heliocentric Model
1543 Nicolaus Copernicus would reintroduce a heliocentric model of the solar system incorporating a new discovery that the earth could possibly be rotating; this was important as the earth was thought to be unmoving, dramatically changing the way in which astronomers mapped the skies in totality.
Nicolaus Copernicus
1576 The very first observatory was constructed in Denmark by Tycho Brahe which used sextants in order to take note of everything in the sky.
Johannes Kepler's law on elliptical orbits
1632 Galileo Galilei proposed ideas that described motion in order to aid his proof for a heliocentric solar system. He was also was able to disprove geocentrism with the discoveries that Jupiter has moons and that Venus went through various phases.
Painting of the first observatory
1619 Johannes Kepler, a student of Tycho Brahe, discovered the three laws of planetary motion using data gathered by the Danish Observatory. These laws helped astronomers to discover that all orbits are elliptical and not always circular.
Isaac Newton
1725 Astronomer James Bradley began to notice that light aberration, which caused objects in space to be displaced slightly from their true position, and nutation of earth’s axis, which are small, periodic changes of the path earth’s axis would take, prohibited the accuracy of astronomy.
Galileo Galilei
1686 Isaac Newton would record the laws of motion he that he developed in the book Principia Mathematica Philosophiae Naturalis based on calculus and Kepler's laws of motion. These discoveries would be monumental for the future of physics.
Aberration of Light
Milky Way Galaxy
1801 Astronomers figured that there were small masses in between Mars and Jupiter. The collection of all of these masses would be known as the asteroid belt.
Stellar Parallax
1846 Astronomers realized that Uranus’ orbit was not matching up with the mathematically predicted schedule. Urbain-Jean-Joseph Le Verrier explained that the gravity from an external planet may have been the cause. Johann Gottfried Galle then discovered the planet Neptune.
Sun
1889 The Doppler effect, a phenomenon that frequency of sound shifts as the source or observer moves farther or closer, was proven to be true for light when Hermann Karl Vogel noticed redshifts from opposing sides of the rotating sun (where the opposing sides were not the axes of rotation); the inverse was also true. This would be important for future astronomical cataloging.
1781 William Herschel would discover the soon to be named planet Uranus. He also hypothesized that changes in positions of stars also meant that the solar system itself was also moving through space and that the solar system was within a larger system which we now know as the Milky Way galaxy.
Asteroid
1838 Friedrich Bessel was able to accurately account for stellar parallax, or the apparent change in position of a celestial body due to the change of earth's position relative to the sun.
Neptune
1859 Spectroscopy was discovered when William Hyde Wollaston noticed that there were missing spots within the color spectrum of the sun which allowed scientists to trace certain properties, from certain elements.
Doppler Effect (Light)
1905 In the early 20th century, physicists were starting to have conflicts with contradictions between Newtonian physics and electromagnetic theory. Albert Einstein created a hypothetical scenario in which all reference frames were capable of physics and that, as mentioned before, the speed of light was constant regardless of the reference frame. We now know these revelations as the special theory of relativity which is also where the famous equation E = mc2 was derived from.
E = mc2
1915 When trying to find a more general application of the special relativity that considered gravity and non-uniform motion, he thought to himself that maybe gravity was a result of the geometrical shape of space and time, or space-time. He thought that larger masses put upon this space-time would cause larger curves that allow for other objects to accelerate upon it. After working out the details and utilizing the theory to solve a problem regarding Mercury’s perihelion, this idea would then be published as the general theory of relativity.
Albert Einstein
1926 A priest named Georges Lemaitre thought that the universe originated from a single atom. Edwin Hubble’s discovery of an expanding universe gave this theory some headway. Robert Wilson and Arno Penzias would later discover cosmic microwave background radiation in 1965. These ideas would soon be known as the big bang theory which would revolutionize cosmology.
Big Bang Art
1929 Edwin Hubble found that the redshifts in distant galaxies were proportional to the distance between the distant galaxies and Earth. He would also attempt to find the constant for the proportional increase of velocity with distance, known as the Hubble constant. This meant that far away objects were accelerating away from our galaxy; the universe had been expanding.
Universe Expansion
1933 Astronomer Fritz Zwicky noticed that there was not enough mass observed in order to hold together clusters of galaxies. He would propose the concept of dark matter, or particles that do not reflect, absorb, or give off light. Later research in 1974 would predict that approximately 90-95 percent of the universe was composed of dark matter. There is still much to be known about dark matter.
Dark Matter Map
1957 The first man-made satellite Sputnik 1 was sent to space from the Soviet Union in order to make observations without interference with Earth’s atmosphere. The very next year in 1958, the U.S. sent Explorer 1 which had radiation detectors installed. This allowed for the satellite to discover the Van Allen Belt, or zones in which charged particles mostly from solar winds are trapped by the Earth’s magnetic field.
Sputnik 1 (Top) and
Explorer 1 (Bottom)
1962 Scientists sent eight Orbiting Solar Observatories which were able to observe the Sun’s corona without optical disturbances from the Earth’s atmosphere. At the same time, the Mariner 2 was sent to space and was able to be in close proximity to Venus. However, it did not have any cameras on it and only contained other instruments such as radiometers.
Mariner 2
1965 The Mariner 4 was sent to space and would be able to capture 22 images of Mars, the first flyby to do so.
Pioneer 10
Mariner 4
1973 The Pioneer 10 would be the first satellite to make it through the Asteroid belt and observe the planet of Jupiter, also sending back pictures of the planet.
1979 The Pioneer 11 would take pictures of Saturn along with the noticeable ring that surrounded it. All of the observations that these satellites made would go on to intrigue many about the strange planets around us and our understanding of them.
Pioneer 11
1990 In 1990, the Hubble Space Telescope was launched into space in order to gain a more accurate measure of the Hubble constant and the deceleration of the universes’ expansion.
Hubble Space Telescope
1998 When interpreting the data of supernovae from the Hubble telescope and other telescopes in 1998, both the Supernova Cosmology Project and High-Z Supernova Search Team found that the universes’ expansion had actually been expanding. They agreed that the concept of dark energy was behind this. However, we still do not understand very many things about dark energy.
Universes' Composition
CURRENT DAY We are still trying to discover all that we can about the fundamental nature of this universe with astronomy. One of the beauties of the subject is that there will most probably always be an aspect of reality that we will strive to understand and that astronomy and physics can be a guide to doing so. It allows for the human to be a part of something that is both literally and metaphorically so much bigger than themselves.