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276 BCE
Eratosthenes is born
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240 BCE
Eratosthenes discovers Earth's tilt
Eratosthenes, during his calculations of Earth's circumference, also discovered that Earth is titled at an angle of 23.5 degrees. This discovery is important because it will later describe how the seasons work. -
240 BCE
Eratosthenes characterizes Earth
Eratosthenes made two huge discoveries about Earth. First, by examining the shadows from the Sun around himself, he determined that the Earth is a sphere. Second, by examining these shadows in different areas, he was able to accurately determine the Earth's circumference. These discoveries are significant because they were some of the first observations of the planet we live on that helped people to visualize it and provided the basis for many scientific discoveries to come. -
194 BCE
Eratosthenes dies
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100
Claudius Ptolemy is born
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150
Claudius Ptolemy's predictions
Ptolemy released a work called the Almagest, which was an astronomy textbook and star catalog that allowed people to predict where a heavenly body would be in the sky from Earth. This is significant because it was the first instance of being able to predict the movements of objects in space, which would later be something people would devote their life to. -
170
Claudius Ptolemy dies
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Feb 19, 1473
Nicolaus Copernicus is born
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1514
Nicolaus Copernicus first reveals his "Heliocentric Universe"
Copernicus was the first to suggest that perhaps our solar system is not geocentric, but rather heliocentric, meaning that all of the planets (including the Earth) revolve around the Sun. This is significant because once people started recognizing the solar system as being heliocentric, it allowed scientists to make additional discoveries to explain happenings on Earth, such as the seasons and night and day. -
May 24, 1543
Nicolaus Copernicus dies
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Dec 14, 1546
Tycho Brahe is born
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Dec 27, 1571
Johannes Kepler is born
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Nov 11, 1572
Tycho Brahe observes a new star
Brahe observed this mysterious star for over a year, until it gradually faded to be out of sight. Today, we know this star as a supernova. Back then, it was proof that things beyond the moon could potentially change, despite Aristotle's beliefs. -
Tycho Brahe proposes Tychonic System
The Tychonic System was a variation of the geocentric model that included traits of the heliocentric model. In this system, all of the planets revolve around the Sun, but the Sun in turn revolves around the Earth. This system was significant because along with this system, Brahe claimed that he did not believe "crystalline spheres" held planets in their orbits, which is what was believed at the time. This opened up the doors of wondering what it was then that held bodies in orbit. -
Tycho Brahe dies
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Kepler's Second Law
Kepler's second law states that the line connecting the planet to the Sun sweeps out equal area in equal time. In other words, Earth may seem travel farther closer to the Sun than it does away from the Sun in a day, but those two areas are actually equal. This is significant because it demonstrates how a planet travels faster when closer to the Sun in order to have the same sweep area as when it is farther away. -
Kepler's First Law
The first of Kepler's three major discoveries claims that all of the planets orbit the Sun in the shape of ellipses, with the Sun lying on one focus of each ellipse. This was significant because it was the first time the idea of perfect circular paths for the planets could be discarded so that we could fully visualize and understand the paths of the planets. -
Kepler's Third Law
Kepler's Third Law states that the period of a planet squared is proportional to its distance from the Sun cubed. This is significant because it helps to explain why Earth travels faster closer to the Sun than away from it, which aligns with the Kepler's Second Law AND the fact that there is more gravitational force when the Earth is closer to the Sun. -
Johannes Kepler dies
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Sir Isaac Newton is born
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Sir Isaac Newton builds a telescope
Newton built the world's first reflecting telescope, which focuses light over a curved mirror. While this telescope still had its flaws, it provided the further technology to build even better telescopes and discover more bodies in the solar system. -
Isaac Newton describes "Universal Gravitation"
Newton was the first to explain that objects are pulled down to Earth by a force called gravity, and not only are objects pulled down, but Earth is also pulled up by gravity. Earth has so much more mass though, that it does not appear to move up at all. This is significant because the concept of gravity was not only used by Newton to describe apples and Earth, but the gravity between planets and moons in the solar system. Scientists finally have an explanation for how we are orbiting the Sun. -
Sir Isaac Newton dies
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Albert Einstein is born
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Albert Einstein reveals E=mc^2
Einstein released this equation to explain how mass can be converted to energy. He suggests that just a little mass can be turned into a lot of energy when multiplied by c^2, where c is the speed of light. This is significant because it explains how the Sun gets energy when transforming the mass of an atomic nuclei to energy. -
Albert Einstein explains his Special Theory of Relativity
Einstein's Special Theory of Relativity basically states that whether we are moving away from light or toward it, it will take the same amount of time to reach us. This is important because this rule only works for light, and units such as time, length, and mass actually depend on the speed we are moving. We can now recognize, though, that the closer to the speed of light we are moving, the bigger differences we will see in these units in comparison to someone moving slower. -
Albert Einstein dies
