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- Ancient people kept track of time and seasons as it affected agriculture.
- Some people even learned to travel using the sun and stars.
- Ancient civilizations kept track of time during the day using the sun and its phases and the night the moon and its phases.
- The modern clock comes from ancient Egypt where the divided daylight into 12 equal parts and we still break down the 24-hour day into 12 hours of A.M and P.M
- Accurate and precise observations that were done over and over again were usually taken before any structures such as the stone-hedge or the Templo Mayor were built.
- Using scientific models, the ancient greeks developed the concept of a "geo-centric" universe (Earth centered universe)
- Ptolemaic model:- the essence of the model was that each planet moves on small circle whose larger centre moves around earth in a bigger circle.
-Islamic leaders took what remained from the Alexandria Library and translated it, then put these documents in an intellectual centre in Baghdad where Islamic scientists used these manuscripts to develop their astronomical knowledge and algebra.
- Most of the official constellation names come from Arabic because of the work of these scholars.
- Copernicus, Tycho and Kepler started to challenge the "earth-centered" idea.
- Kepler's key discovery was that planetary orbits are ellpises instead of circle shaped; the "Copernican Reveloution"
Keplers's 3- laws of planetary motion:-
Kepler's first law: The orbit of each planet around the sun is an ellipse with the sun at one focus (the planet's distance varies during its orbit)
Kepler's second law: As a planet moves around its orbit, it sweeps out equal areas in equal times.
Kepler's third law: More distant planets orbit the sun at slower average speeds.
- Galileo finally solidified evidence that it was a sun centered solar system rather than an earth-centered solar system by answering the 3 basic objections by Aristotle and other ancient Greeks:-
1-Aristotle held that the earth could not be moving because it if it objects such as such as birds, falling stones and clouds would be left behind as earth moved along.
Galileo:- Experiments with moving balls were used to demonstrate that a moving object remains in motion unless a force comes to stop it. This insight explains why objects that share the Earth's motion through space (such as bird, falling stones...) would not be left behind. (same idea explains why passengers stay with a moving place even when they leave their seat)
2- The idea of non circular orbits contradicted Aristotle's claim that the heavens-the realm of the sun, moon planets and stars must be "perfect and unchanging"
Galileo:- Built an effective telescope and saw "sunspots" on the sun and moon which were considered "imperfections" at the time. If the heavens were not "perfect" then the idea of elliptical orbits (rather than "perfect" circles) was not so objectionable.
3- No one had detected Stellar parallax that should occur if the Earth orbits the Sun.
Galileo:- He saw with his telescope the our universe resolved into countless individual stars dispersed. This discovery helped him argue that the stars were far more numerous and distant than Tycho believed.
What is a scientific theory?- A scientific theory is a simple yet powerful model that explains a wide variety of observations in terms of just a few general principles and has attained the status of a theory by surviving repeated and varied testing.