Seas ons

By Cammi e Goodman

Because of the tilt of the Earth, the direct rays of the sun are focused on

different areas of the globe at different times of the year

The area receiving the most direct rays will receive much more solar energy that the parts receiving indirect, slanted rays.

The more slanted the rays of the sun the fewer strike a given area and less heat energy is transmitted.

This unequal heating drives our weather and causes the seasons.

Seasons determine the changes in temperature, precipitation, amount of daylight, and plant growth.

If the Earth were not tilted, there would be no seasons.

We would experience conditions like those during the equinoxes all year.

Explore a model of Earth's daily rotation

Meteorological seasons vary from place to place; they are based on general

climatic conditions The astronomical seasons are the

ones marked at specific intervals on our calendars.

That’s why you may have cold weather long before December 21, the astronomical beginning of winter.

Temperate climates have four seasons: autumn, winter, spring, and summer.

Locations near the Equator generally experience two seasons, dry and rainy.

The Polar Regions also have two season, light and dark.

The sun’s rays determine climate belts on Earth.

On June 21 and December 21, the uppermost and lowermost rays of the sun mark the imaginary Arctic and Antarctic Circles.

These lines begin the area where, for one day or more, the sun does not set (June-Northern Hemisphere, December Southern Hemisphere), or rise (December-Northern Hemisphere, June-Southern Hemisphere).

•On those same days, the central, or most direct rays of the sun, mark the Tropics of Cancer and Capricorn. •These are the uppermost and lowermost overhead positions of the sun in relation to the Earth.

Causes of Four Seasons

•During the year, Georgia has summer, fall, winter, and then spring.

As the seasons change you notice changes in the weather.

Summer in Georgia is often hot.

Winter is much cooler. • Spring and fall are

milder.

Why is it warmer in summer than in winter?

Recall that Earth rotates on its axis like a top.

When a top spins, the axis points straight up and down. But Earth is not a top.

Earth’s axis is not straight up

and down. Instead, it tilts.

This means part of Earth leans toward the sun while another part leans away.

•Imagine a line around the middle of Earth. The equator is an imaginary

line that divides Earth in half. Each half of Earth is a

hemisphere. The half of Earth above the

equator is the Northern Hemisphere.

The half of Earth below the equator is the Southern Hemisphere.

• 

When the Northern Hemisphere tilts toward the sun, it is summer in the Northern Hemisphere.

The sun’s rays heat the Northern Hemisphere more than the Southern Hemisphere.

Earth Revolves around the sun animated diagram

Earth Moves in two ways You know that Earth rotates, or spins on its axis. This causes night and day. Earth also revolves, or moves in a path around

the sun. Recall that this path around the sun is Earth’s

orbit. Earth takes one year to go all the way around

the sun one time.

Day and Night Animation

You can see that Earth’s axis tilts. As Earth revolves, different parts of Earth tilt

toward the sun. Notice the tilt when it is summer in the

Northern Hemisphere. The northern half of the planet tilts toward the sun.

Now notice Earth’s tilt when it is winter in the Northern Hemisphere. The northern half of Earth tilts away from the sun.

Explore a model of Earth's yearly revolution around the sun.

•Look at the seasons in the Southern Hemisphere. When it is summer in the Northern Hemisphere, it

is winter in the Southern Hemisphere. When it is winter in the Northern Hemisphere, it is

summer in the Southern Hemisphere.

In places near the equator, the weather does not change much from one season to the next.

During spring and fall, neither hemisphere tilts toward the sun.

The sun heats the two hemispheres evenly. Temperatures are milder.

Length of Day and Night •How long day and night are also changes with the seasons. The change in day length also affects the

temperature. In summer, the days are longer. So, the sun heats

Earth’s surface longer each day in summer. In winter, the days are shorter. So, the sun heats

Earth’s surface for a shorter time each day in winter.

This is one of the reasons that winter is cooler than summer.

Interactive Moon, Sun and Earth

Discussion Question

Why do Georgia and Alaska have summer at

the same time?