Mrs. Degl 1

Earth’s Motions in Space

Topics that are covered:

1. Geocentric Model2. Heliocentric Model3. Rotation4. Revolution5. Precession

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Geocentric Model

This model of the solar system suggests that Earth is in the center and it is stationary while the other planets, and the Sun, revolve around it.

Ptolemy (85-165) came up with this model.

Is this correct?

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Heliocentric ModelNicolai Copernicus (1473-1543) came up with this.

This model says that the Earth, and each of the other planets, rotate on their own axis, while they revolve around the Sun.

This is the correct model of our solar system.

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Rotation

                      

The Earth rotates 15º of longitude every hour, from West to East.

There are a few proofs that the Earth rotates.

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Proofs that the Earth rotates:

1. Sunrise/Sunset or Day/Night

2. Star Trails (the stars appear to move across the sky during the night)

3. Coriolis Effect (objects in the air seem to curve before they land)Cannons and arrows miss their targets when aimed straight on.Winds and ocean currents are also curved because of rotation.

http://daphne.palomar.edu/pdeen/Animations/34_Coriolis.swf

4. Foucault Pendulum/Free Swinging Pendulum

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Can you find Polaris?

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Revolution

The Earth revolves around the Sun once every year.

How many days is that?

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Proofs that the Earth revolves around the

1. Star shiftConstellations that are visible in one part of the sky

during one season are not going to be in the same part of the sky during the following season. This is because the Earth is revolving around the Sun and facing different parts of the night sky during different seasons. Since there is 360 º in a circle, it takes about 360 days (@ 1 year) for the Earth to be facing the same part of the sky again. That means that the positions of constellations in the sky change by about 1º per night.

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2. Doppler Effect

This is the distortion of a wave (light or sound) caused by objects moving closer together or further apart from each other.

As the Earth moves towards stars, the light waves are compressed. This is called a Blue shift. Blue is one of the shortest wavelengths.

As the Earth moves away from stars, light waves are stretched out. This is called a Red Shift. Red is one of the longest wavelengths.

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Polaris is not going to be the North Star forever.

Every 26,000 years, the Earth tips the other way, just like a spinning top.

Scientists call this earth motion “Precession” or wobble.

Precession