SPACE

Day/Night and Seasons

Objective

To model and illustrate how the tilt of the earth rotates on its axis, causing day and night and how it revolves around the Sun causing changes in the seasons

How does the Earth move?

Long ago, people thought that the Earth stood still while the Sun moved

We now know that the Earth moves around the Sun

The Earth REVOLVES around the Sun The Earth ROTATES while it revolves

around the Sun

Day and Night We have day and night

on Earth because of the EARTH’S ROTATION – the earth spinning around and around. (1670 km/hr)

Day and night

It takes 24 hours for the Earth to ROTATE once.

The Earth is kept in orbit by the force of…The Earth is kept in orbit by the force of…

GravityGravity

…and by the fact that is is moving at a high velocity

Why are there seasons?

Earth not only spins on its axis, it also revolves around the Sun

Earth’s trip around the Sun takes 365¼ days, or one year

Every 4 years, we add a Leap Day to account for the extra ¼ days

Earth's path, or orbit is shaped like an ellipse or a flattened circle

The tilt of the Earth is the reason for the seasons

The Earth is divided up into the northern hemisphere The Earth is divided up into the northern hemisphere and the southern hemisphere:and the southern hemisphere:

Equator

Northern hemisphere

Southern hemisphere

Seasons

If the Earth was perfectly balanced, as it is in this animation, we wouldn’t have different seasons and the sun would always rise and set at the same time every day.

Seasons

Every part of the Earth would receive an equal amount of sunlight as the earth rotated.

But the Earth isn’t perfectly balanced, it’s tilted on its axis…

…and it’s REVOLVING around the sun.

The tilt changes how much sunlight each part of the earth receives.

It is this tilt which makes our days longer or shorter and it’s what causes the seasons.

Seasons

The tilt does not change – it always remains pointed in the same direction

As the Earth revolves around the Sun, the tilt sometimes points toward the Sun, sometimes away from the Sun, and sometimes neither away nor toward the Sun

Summer season

In June, the North Pole tilts toward the Sun.

The northern half of Earth (Northern Hemisphere) receives more direct sunlight

Daylight hours are longer and temperatures are warmer.

June 21st - Summer Solstice

This is our summer

What season does the Southern Hemisphere

experience in June?

Winter season

In December, the North pole tilts away from the Sun.

The northern half of Earth (Northern Hemisphere) receives less direct sunlight

Daylight hours are shorter and temperatures are colder

December 21st – Winter Solstice This is our winter

What season does the Southern Hemisphere

experience in December?

Spring and Fall Seasons In March and September, neither

the top or bottom half of Earth is tilted toward the Sun

In spring and fall, the top and bottom parts of Earth (Northern and Southern hemispheres) receive the same amount of direct sunlight

The amount of daylight is close to 12 hours and the temperatures are more moderate

March 21st – Vernal Equinox September 21st – Autumnal

Equinox This is our spring and fall

What season does the Southern Hemisphere

experience in March? In September?