EARTH’S PLACE IN THE UNIVERSE

REVOLUTION, ROTATION, & LOCATION

STARTER

Which statement describes the motion of Earth around the sun?

A. The speed of Earth is constant regardless of its distance from the sun.

B. The speed of Earth is constant because the distance remains the same between Earth and the sun.

C. Speed increases the farther Earth is from the sun and decreases the closer it is to the sun.

D. Speed increases the closer Earth is to the sun and decreases the farther it is from the sun.

THE SUN

Center of our solar system

Source of all energy in our solar system

Moves as planets tug on it so it orbits the solar system’s midpoint or barycenter

BARYCENTER

Point between two objects where they balance each other

barycenter animation

MOVEMENTS OF EARTH

Revolution: The movement of the Earth around the sun.The Earth moves around the Sun constantly at an average speed of 106,000 km/hr.

Revolution (or Orbital Period) = 365.24 days

MOVEMENTS OF EARTH

Rotation: The movement of the Earth as it spins on its axis. 1 rotation = 24 hours side facing sun = daytime side facing away from sun = nighttime creates the “setting” and “rising” appearance of the sun

THE REVOLVING EARTH

Because of the elliptical shape of the orbit, the earth is not always the same distance from the sun (perihelion & aphelion)

THE REVOLVING EARTH

The “tilt” of Earth’s axis is about 23.5 degrees

As the earth revolves around the sun, its point of axis does not change – always points to Polaris (North Star) for now

PRECESSION

Change in direction of axis, without any change in tilt

Changes stars near the Pole but does not affect seasons (angle stays same)

Like a spinning top

Polaris will not always

be the North Star

Precession video

THE REVOLVING EARTH

When the point of axis is TOWARD the Sun

Northern Hemisphere has longer periods of daylight & warm temperatures (summer)

Southern Hemisphere has shorter periods of daylight & cooler temperatures (winter)

THE REVOLVING EARTH

When the point of axis is AWAY from the Sun

Southern Hemisphere has longer periods of daylight & warm temperatures (summer)

Northern Hemisphere has shorter periods of daylight & cooler temperatures (winter)

NORTHERN & SOUTHERN HEMISPHERES

EQUATOR

NORTHERN HEMISPHERE

SOUTHERN HEMISPHERE

THE REVOLVING EARTH

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0408/es0408page01.cfm?chapter_no=visualization

NUTATION

Wobbling around the axis

Changes the angle by ½ degree one way or the other

Occurs over 18 year period

Caused by moon

Slight decrease or increase of seasons

VOCABULARY CARDS

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