Ancient Astronomers

Eratosthenes

276 BCE

He was a Greek mathematician who used the Sun to measure the size of the round Earth. He was proving all of the flat Earth believers wrong and this is relevant because in today's society there was a debate once again as to whether the Earth was flat.

Claudius Ptolemy

100 BCE

Around 100-170 AD. Ptolemy also developed the Earth centered universe model. This model was adopted for close to 1500 years, and was incorrect. Ptolemy reasoned that the planets move in smaller circles in their larger circle orbit around the Earth, these smaller circles were called epicycles. This is important to know because the planets do not revolve around the Earth.

Nicolaus Copernicus

1543

In his work, "De Revolutionibus Orbium Caelestium," published in 1543. He explained his new heliocentric, or sun centered, model. He believed that the motion of the earth around the sun explained the motion of the planets better than Ptolemy's epicycle theory. This theory is important because we still use this model today

Johannes Kepler

1571

Using the careful observations of Tycho Brahe, Kepler devised three laws that govern planetary motion.This is important because Kepler was able to predict the future position of planets with greater accuracy. The three laws are planets travel in elliptical orbits around the sun, A line from the planet to the sun sweeps out equal areas in equal times, and the square of the orbital period of a planet is equal to the cube of their distance from the Sun.

Tycho Brahe

1577

Brahe observed a supernova in the constellation of Cassiopeia. Brighter than Venus, the new star remained visible for a year and a half. This is important because his precise measurements revealed that the supernova never changed with regard to the surrounding stars, and that the comet orbited beyond the path of the moon, contradicting the idea that the heavens never changed.

Sir Isaac Newton

1642

Newton formulated the basic laws of motion that are the basis of mechanics. He published these laws in his work, Philosophiae Naturalis Principia Mathematica. These laws are important because they explain all about energy and forces that we use in everyday life.The three laws are: an object at rest stays at rest until a force is acted on it, acceleration is produced when a force acts on the mass and for every action there is an equal and opposite reaction.

Albert Einstein

1921

The equation that helped explain special relativity – E = mc2 – is famous even among those who don't understand the underlying physics. He also is known for his work on general relativity and the photoelectric effect; his work on the latter earned him a Nobel Prize in 1921. His formula for relativity is important because we still use the formula in physics to this day.