Key Astronomers and Physics Discoveries Timeline

Key Figures in Astronomical and Physical Science

Aristotle

• Proved that the Earth is spherical.
• Believed that the Earth was at the center of the universe.

Aristarchus

• He was the first to state that the Sun, and not the Earth, was the center of our universe.
• Used simple geometry to estimate the size of the Sun and Moon and their relative distances.

Ptolemy

• Made a model called the Ptolemaic system, concluding all astronomical objects move at constant speeds in circular orbits.
• Ptolemy built his model to fit this idea. The Ptolemaic model is one of the longest upheld scientific theories in history; it was the cornerstone of astronomy for 1,500 years.

Copernicus

• Concluded that the Sun was the center of the universe instead of the Earth.
• Promoted the concept of Heliocentrism.

Brahe

• Made super precise instruments for observing space before the telescope was created.
• Believed the universe was a blend of the Ptolemaic and Copernican models, creating his own model in which the planets orbit the Sun and the Sun orbits the Earth.

Kepler

• Kepler’s 1st Law: All planets move about the Sun in elliptical orbits, having the Sun as one of the foci.
• Kepler's 2nd Law: A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.
• Kepler’s 3rd Law: The squares of the sidereal periods (of revolution) of the planets are directly proportional to the cubes of their mean distances from the Sun.

Galileo

• Invented the telescope.
• Observed that four moons revolved around Jupiter.

Newton

• Invented Calculus.
• Proposed the force of gravity was what was holding the solar system together.

Einstein

• Theory of Relativity: Determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers.
• The photoelectric effect is the emission of electrons or other free carriers when light is shone onto a material. Electrons emitted in this manner can be called photoelectrons.

Newton (Further Contributions)

• Newton's First Law of Motion - sometimes referred to as the law of inertia. An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
• Newton's Second Law of Motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.