16 CENTURIES
From the time of Claudius Ptolemy to the time of Nicolaus Copernicus, it was the Ptolemaic model that was accepted.
Thales (625 - 546 BC) - prediction of the eclipse of the sun in May 28 585 BC.
Pythagoras (582 - 500 BC) - considered the Earth as a globe revolving with the other planets
Anaxagoras (500 - 428 BC) - explained eclipses and believed the moon was part of Earth
Eudoxus (408 - 355 BC) - first to explain the movement of planets
Heraclides (387 - 312 BC) - proposed the sun is the center of the solar system;observed Mercury and Venus
Pytheas (380 - 300 BC) - observed the Pole Star is not the true pole and that the moon affects the tides
Pre-Copernican Astronomy
The Golden Age of Astronomy
Nicolaus Copernicus
Nicolaus Copernicus (1473 - 1543)
Polish Canon
De Revolutionibus Coelestium Orbium
Heliocentric Model
Father of Modern Astronomy
The Copernican System
Placed the Sun at the center
His theory did not predict planetary positions accurately
Retained epicycles and deferents
The Copernican theory was wrong but the Heliocentric idea was right.
Tycho Brahe(1546-1601)
Called Tycho, the man with the golden nose.
Studied for law but went to astronomy and mathematics
The Observational Astronomer
Tycho’s Work
Found errors in the astronomical tables of the times
Studied the motion of planets
in 1572, observed the supernova (Tycho’s supernova)
Carefully gathered data about planetary positions
Tycho’s Theory Believed earth was stationary
Rejected the Ptolemaic theory because of its wrong predictions of positions of heavenly bodies
Made the earth the immobile center of the universe
Devised new and better instruments
Hired an assistant, Johannes Kepler
Tychonian Model
Earth is the immobile center
The moon orbits around earth.
The sun orbits the Earth!
Planets orbit around the sun.
Johannes Kepler
Johannes Kepler (1571-1630)
Three Laws of Planetary Motion
His Book: Harmonice Mundi (The Harmony of the World)
Kepler’s Theory Abandoned CIRCULAR MOTION
Instead, he discovered the ELLIPSE as the orbit of Mars
Discovered that planets do not move at constant speed
In his book, he came within a paragraph of discovering the law of mutual gravitation.
Laws of Planetary Motion
The Three Laws of Planetary Motion
1st Law:Law of Ellipses
All planets revolve around the Sun in orbits that are ellipses, and the sun
is located at one of the foci.
2nd Law: Law of Equal Areas
A line drawn from the planet to the sun sweeps out over equal areas
in equal intervals of time.
3rd Law: Law of Harmony
The square of the period (in earth years) of a planet is equal to the cube of its average distance (in astronomical units) to the sun.
T 2 α r 3
By now, it is clear the planets revolve around the sun and the orbits are not circles but
ellipses. The next question is:
What keeps the planets moving around the sun?
Galileo Galilei
Galileo Galilei(1564 – 1642)
Defender of Copernicanism
Made important discoveries about motion.
Defended the theory that the Earth moves.
Earth moves.
Galileo Galilei
Made telescopes & used it for astronomy
Discovered the moons of Jupiter, the phases of Venus and the sunspots
Taught that the Earth moves
Fell into controversy with the church authorities
Believed that the Earth is not the center.
Question:
If planets move, what or who keeps them moving?
Principle in those days: Principle in those days:
Quidquid movet, ab alio moveturQuidquid movet, ab alio movetur..
Whatever is moving, is moved by another?Whatever is moving, is moved by another?
So what moves the planets?So what moves the planets?
Galileo’s Answer:
There is no need for a mover. The planets go on by themselves. Galileo studied motion and
found that once a body is in motion, it will tend to continue in that state of motion.
Nothing!Nothing!
(Yeah it sounds like Newton, who later (Yeah it sounds like Newton, who later borrowed it and made it borrowed it and made it hishis first law.) first law.)
Galileo had explained…
what moves planets (the red line) is inertia.
The remaining question is what keeps them in
orbit? Gravitation, which brings us to
Newton.
Isaac Newton
Isaac Newton (1642 - 1727)
His great work: Principia Mathematica Philosophiae Naturalis Mathematical Principles of Natural Philosophy
Law of Gravitation
The Principia
For Isaac Newton there is only one remaining
question…
If planets tend to go on along straight lines, why
do they not fly off into space?
Newton’s Solution
Any mass (object) exerts a force called gravitation.
Gravitation is the property of a mass to pull other masses to itself.
Between a chair and table, between an apple and the earth, between the sun and the planet there is attraction.
Inertia makes a planet move along a straight line but at the
same time, there is a pull exerted by the Sun on a planet. The
result is that the planet does not fly to space nor does it fall to the
sun. The combined motion becomes the elliptical orbit
around the Sun.
Two motions happen at the same time.
The planet tends to fly off.
Gravitational force pulls the planet to the center.
Result: the orbital motion
In these 99 years (1543-1642), it has been established:
That the sun is the center of the solar system
That the Earth moves.
That planets move in elliptical paths.
That the orbits are maintained by inertia and gravitation.
Write TRUE if the statement is correct and if False, WRITE the word/s that makes the statement incorrect and opposite to it is the correct answer.Ex if false: Blue -> Red
1. Johannes Kepler believed that the earth is the immobile center.2. Copernicus heliocentric idea was correct and predicted the planetary positions accurately.3. Kepler improved the telescope that brings the discovery of the different phases of the Venus.4. Tycho hired Kepler as an assistant.5. Isaac Newton gives the Law of Planetary Motion.6. Galileo defend Copernicus heliocentric idea.7. Eratosthenes was famous for his measuring earth’s diameter.8. Hipparchus invented the armillary sphere.9. Ptolemy proposed the spherical universe.10. Aristarchus was the first to push the idea of heliocentric system.
