ANCIENT CONCEPT OF HEAVENS

Ptolemy and the Geocentric Model

• Geocentric Model (Geo means Earth and Centric means Center)

• The model that says the earth in the center of the Solar System (earth-centered)

• Greek philosopher Ptolemy thought that the Earth is at the center of the Solar System

• The Catholic Church believed this model because God placed Earth at the center.

Claudius PtolemyClaudius Ptolemy

Devised the Geocentric Model of the Universe.

4 Arguments for the Geocentric Model

• The first argument given,to support the Geocentric Model was that if the Earth revolved the Sun, then we would feel the Earth’s motion. But since the Earth’s motion could not be detected then the Earth, they thought, could not possibly be moving.

But there are actually (5) ways in which the Earth does in fact move:

1) The Earth is rotating

on its imaginary axis.

2) The Earth is revolvingaround the Sun.

3) The Earth is “precessing”,

or wobbling, on its axis.

4) The Sun is revolving

around the center of the Milky Way.

separating

5) The galaxies are moving apart, as a result of the Big Bang.

June December

2) We Don’t Observe Stellar Parallax2) We Don’t Observe Stellar Parallax

parallactic shift

Heliocentric Model

3) The Moon Could Not Keep Up 3) The Moon Could Not Keep Up

The third argument given in support of the Geocentric Model was that if the Earth orbited the Sun,that the Moon would lag behind.

4) Objects Would Fly Off Earth 4) Objects Would Fly Off Earth

The fourth argument given in support of the Geocentric Model, had to do with the Earth’s rotation on its axis. If the Earth were to rotate on its axis, the ancients believed, then anything not nailed down would fly off into space. Since the ancients failed to observe objects flying off into space, then they incorrectly concluded that the Earth must not be rotating.

The Geocentric ModelThe Geocentric Model

Since none of these questions could be answered, then Ptolemy and the Geocentric Model remained unchallenged for 14 centuries.

HELIOCENTRIC MODEL AND COPERNICUS

Heliocentric Model

• Heliocentric Model -Helio means Sun and Centric means Center)

• The model that says that the Sun is at the center of the Solar System (Sun-centered)

• Nicolaus Copernicus proposed that the Sun was the center of the universe, not the earth.

Heliocentric Evidence• The Catholic Church opposed this model

because it went against the church’s beliefs and imprisoned, tortured and killed people who believed this model

• Evidence –Seasons–Telescope (Galileo)–Ellipses (Kepler’s Law’s)–Gravity (Newton)

The Origin of the Solar System

The Nebular Hypothesis in its original form was proposed by Kant and Laplace in, 18th century.

•

Collapsing Clouds of Gas and Dust

• A great cloud of gas and dust (called a nebula) begins to collapse because the gravitational forces that would like to collapse it overcome the forces associated with gas pressure that would like to expand it (the initial collapse might be triggered by a variety of perturbations---a supernova blast wave, density waves in spiral galaxies, etc.).

In the Nebular Hypothesis, a cloud of gas and dust collapsed by gravity begins to spin faster because of angular momentum conservation.

• The law of conservation of angular momentum states that when no external torque acts on an object or a closed system of objects, no change of angular momentum can occur.

The Spinning Nebula Flattens

• Because of the competing forces associated with gravity, gas pressure, and rotation, the contracting nebula begins to flatten into a spinning pancake shape with a bulge at the center.

The collapsing, spinning nebula begins to flatten into a rotating pancake

Condensation of Protosun and Protoplanets

• As the nebula collapses further, instabilities in the collapsing, rotating cloud cause local regions to begin to contract gravitationally. These local regions of condensation will become the Sun and the planets, as well as their moons and other debris in the Solar System.

As the nebula collapses further, local regions begin to contract gravitationally on their own because of instabilities in the collapsing, rotating cloud.

END !!!

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