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Around 2700 B.C. the Celts (Druids) built Stonehenge.

Stonehenge was likely an astronomical building, it aided in the observation of the sun, moon and planets.

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The Egyptians have a written record that they built the pyramids with regard to the heavens.

They also had calendars and time keeping.

The Ancient Egyptians had cosmologies as early as 1318 B.C.E..

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Starts with the Greek philosophers in the 7th century B.C..

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Geocentric model:

People believed that earth was at the centre of the universe,

That earth was not moving,

That all the planets and stars revolved around earth,

And that celestial bodies were perfect and unchanging

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Around 550 B.C.E.

Pythagoras proposed that the Earth, Moon, Sun, and planets were all spherical

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408-355 B.C.E.

Proposed the Geocentric model: cosmology of 27 concentric spheres with earth at the centre.

He compiled most of the modern northern constellations

He build the first observatory in Greece.

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384 - 322 B.C.E.

Aristotle believed that the Universe is governed by physical laws.

He still believed in the Geocentric model.

He noted that the earth cast a spherical shadow during a lunar eclipse.

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Around 300 B.C.E.

He broke tradition and believed in the Heliocentric model : earth is the 3rd planet from the sun, and the moon orbits the earth. Aristarchus believed that the earth had two motions: orbiting the sun, and rotating on its own axis.

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Much of the knowledge of the universe (in western society) was stored in the library at Alexandria.

It was burned down in 47 B.C. and many items were lost.

Much of what we have on early astronomers comes from Ptolemy.

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276 - 194 B.C.E.

Eratosthenes measures Earth's circumference (42,000 km).

Combined with Aristarchus's relative sizes, he found:

Earth-moon distance as 4 x 10^5 km (actually 3.84 x 10^5 km)

Earth-sun distance 10^7 km (actually 15 x 10^5 km)

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190 - 120 B.C.E.

Hipparchus believed in Pure Observations.

He examined the precice position of the stars, but was unable to discover parallax (that the earth is moving). The parallax satellite is named after him (HIPPARCOS).

He found the procession of the equinoxes, and gave us a modern magnitude system for the brightness of stars:

Brightest starts = 1st magnitude

Faintest stars = 6th magnitude

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127 - 150 A.C.E.

He was the last of the Great Astronomers of Alexandria, and hid away in the library of Serapeum. Ptolemy wrote the Mathematical Syntax or Almagest. Ptolemy was the last word of astronomy until copernicus in 1500 A.D..

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Early astronomers did not understand the motion of the planets in a geocentric model. Movement from E to W (prograde motion) was simple, but occasional movement from W - E (retrograde motion) was difficult to explain.

Ptolemy envisioned a system of two circles for each planet and the sun with earth at the centre:

The Deferent: moves on the orbit

The Epicycle: moves on the deferent

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Each planet is treated independently from other planets

It has no universal rule for all planets

Middle ages astronomers thought it was too complex

A good system needs simple underlying principles

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Astronomy and science halted in the western world during the dark ages (after the fall of the roman empire), but it continued in other cultures:

China (sunspots recorded as early as 28 B.C.)

Japan

Indigenous peoples (Aztecs, Maya, others) (Medicine wheel, Light dagger, Aztec temples, etc.)

India and Persia

Islam (Recognised the need for observation to confirm theory, many stars names are Arabic in origin)

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1473-1543

Copernicus was a polish/german astronomer who was also a lawyer, physician, economist, canon of the church, and an artist.

He coined the heliocentric model.

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The sun is the centre of the galaxy, and earth is the third closest planet. This helped explain venus, and mercury, and the concept of retrograde.

Copernicus was still influenced by the church and insited upon perfectly circular orbits.

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1546 - 1601

Tycho Brahe was the court astronomer of the King of Denmark, and the king built the Uraniborg observatory for him. He had a very interesting lifestyle.

He rejected Ptolemy and Copernicus' models and came up with the Tychonis system:

Moon and sun orbit earth

all other planets orbit sun

He contributed many precise position measurements of planets, comets and supernovae.

Tycho argued that parallax should be able to be measured for nearby objects, but he failed to detect parallax. From this he concluded that all these objects must be very far away.

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1571 - 1630

Keppler was a German priest who became Tycho Brahe's assistant in 1600. He inherited all the position data collected and used it to redefine the Copernican model. His changes were that the planets had elliptical orbits instead of perfect circles.

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1. Planets move in ellipse with the sun at one focus

2. A line joining planet and sun sweeps out equal areas in equal time intervals

3. The size of the orbit and the period are related by this equation: the squar of a planet's orbital period (P) is proportional to the cube of its semi major axis (a)

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1564 - 1642

Galileo delivered the final blow to the geocentric model. He had much trouble with the Catholic church (Pope Paul V) for the statement that objects fall at the same rate, and that his observations did not reconcile with the writings of the Bible, Aristotle, or Plato. in 1906 he learned of a telescope made by a dutch optician and made his own version. Here's what he saw:

Phases of Venus (including changes of size)

Mountains on the moon

Sunspots on the sun

Moons of Jupiter

Individual Stars in the Milky Way

Rings of Saturn

His last years were spent under house arrest by the Roman Catholic Church due to 'vehement suspicion of heresy'

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1642 - 1727

Sir Isaac Newton finally put the whole picture together and began the devellopement of Physics and Calculus. He devellopped two sets of laws:

Newton's laws of gravitation:

A body will remain at rest or moving in a straight line at a constant speed unless acted upon by an outside force

F=ma

Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on the first

Newton's law of Gravitation

Two bodies attract each other with a force directly proportional to the mass of each body and inversely proportional to the square of the distance between them

This law explains Keppler's laws of planetary motion