UNIT 3: EARTH-SUN RELATIONSHIPS

Part 1:Planetary Motions and the

Seasons

Unit Objectives

Upon completion of this unit, TSWBAT:1. Examine the earth’s motions

relative to the sun2. Describe the significance of the

tilt of the Earth and how it affects the seasons.

3. Explain the atmospheric processes associated with weather.

4. Label the trade winds of the earth.

5. Discuss the importance of ocean currents.

Earth’s Planetary Motions

Earth is strategically placed as the third planet in the solar system.

The sun is at the center of the universe. Without it, life as we know it cannot exist.

It is 750 times the mass of all the planets combined!

The earth is located 150 million km from the sun.

Recently, Pluto’s label as a planet (1930) was removed in 2006.

The Solar System

The earth’s natural environment, such as its vital heating, is shaped by its movement on an orbit around the sun.

The earth is tilted 23 ½ degrees. The earth rotates in an west-to-east

direction. As you may recall, the earth makes one

full rotation on its axis every 24 hours (23 h 56 m).

It takes the earth 365 ¼ days to make one full revolution around the sun.

In order to count the ¼ day, scientists created the leap year. This occurs every 4 years.

The Earth’s Tilt

In unit 1, you learned the earth is an oblate spheroid.

From pole to pole, the diameter of earth is 7,900 miles.

Around the equator, the earth is 7,927 miles-a difference of only 27 miles.

The earth’s circumference at the equator is approximately 25,000 miles.

A city located near the equator, such as Quito, Ecuador, rotates at a speed of 1,040 miles per hour! (Why can’t its citizens feel it?)

However, it would take you 24 hours to make a full turn in place if you stood at the North or South poles!

This contrast between the force of rotation creates the slight bulge at the equator.

We do not notice the earth’s rotation because everything (land, water, air) moves at the same rate of speed.

The rate of rotation does not vary-the earth does not slow down or speed up).

Moving currents of water and streams of air are affected by the Coriolis Effect.

If you enter the Southern Hemisphere, the ocean currents move in the opposite direction.

This phenomena plays a major role in the earth’s climate, weather, ocean currents, and even the environment.

The Seasons

Seasons are the result of the tilt of the Earth's axis. Earth’s axis is tilted 23.5°. This tilting is why we have SEASONS like fall,

winter, spring, summer. The number of daylight hours is greater for the

hemisphere, or half of Earth, that is tilted toward the Sun

Solstices occur twice a year, when the tilt of the Earth's axis is oriented directly towards or away from the Sun, causing the Sun to appear to reach its northernmost and southernmost extremes.

Winter solstice is the shortest day of the year. In the Northern Hemisphere. It occurs on December 21 and marks the beginning of winter.

The Summer Solstice is the longest day of the year. It occurs on June 21 and marks the beginning of summer

Equinoxes

A day lasts 12 hours and a night lasts 12 hours at all latitudes.

Equinox literally means "equal night". Sunlight strikes the earth most directly at

the equator. This occurs twice a year. The vernal (spring) equinox occurs

March 21. The autumnal (fall) equinox occurs

September 21

The Seasons