Earth-Centered to a Sun-Centered System

Mayan Astronomers discover an 18.6-year cycle in the rising and setting of the Moon.

750 BCE

Thales speculated that the Sun and stars were not gods, but balls of fire.

600 BCE

Pythagoras believed nature can be described by numbers, and proposed that the Earth was spherical.

530 BCE

Babylonians use the zodiac for better ways to record and communicate information about the position of celestial bodies.

400 BCE

Plato has the idea that everything in the universe moves in harmony and that the Sun, Moon, and planets move around Earth in perfect circles.

387 BCE

Aristarchus

200 BCE

He was the first to say that the Sun, and not the Earth, was the center of our universe.

Ptolemy

100

Ptolemy extended the observations and conclusions of Hipparchus, by creating his own theory. (Ptolemy Theory)

Geometric Model

140

Ptolemy proposed a planet moves in a small circle called an epicycle, and the center of the epicycle moves along a larger circle around the Earth.

Christianity v. Astronomers

150

Greek astronomical knowledge was condemned and hidden by Christians. Creating a division of Astronomers v. Christians

Parallax

189

Definition: the position or direction of an object appears to differ when viewed from different positions.
First used by Hipparchus, who used observations of a solar eclipse from two different locations to measure the distance to the moon.

Aristotle

384

He established a geocentric universe in which the fixed, spherical Earth is at the center, surrounded by concentric celestial spheres of planets and stars.

Hindu cosmological time cycles explained in the Surya Siddhanta, give the average length of the sidereal year as 365.2563627 days, which is the most accurate estimate of the sidereal year in the world for over a thousand years.

400

Aryabhata writes how the planets and the Moon reflect the light of the Sun, and that the Earth rotates on its axis causing day and night and the revolution around the sun causing years.

499

Astrolabe is constructed by Mohammad al-Fazari, which is a measurement of the positions of stars and planets

928

Bhāskara II calculates the longitudes and latitudes of the planets, lunar and solar eclipses, risings and settings and conjunctions of planets. As well the planetary mean motion, ellipses, the lunar crescent and the seasons.

1150

Heliocentric Model - Copernicus

1543

The Sun is assumed to be at a central point with the Earth and other bodies revolving around it.

Brahe

1600

He developed astronomical instruments and helped in measuring and fixing the positions of stars that paved the way for future discoveries.

Ellipses

1602

Definition: a closed, symmetric curve shaped like an oval, which can be formed by intersecting a cone with a plane that is not parallel or perpendicular to the cone's base. (celestial objects in periodic orbits around other celestial objects all trace out ellipses) Founded by Kepler.

Kepler - planetary laws of motion

1650

Founded three major laws of planetary motion.
1) the planets move in elliptical orbits with the Sun at one focus.
2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc.
3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits.