Aim: What causes Seasons?

Do Now: What is the difference between

revolution and rotation?

Notepack 28

Earth’s rotation • The Earth rotates on its axis

(imaginary vertical line around which Earth spins) every 23 hours & 56 minutes. (counter clockwise)

• One day on Earth refers to the length in time that it takes for one rotation of the Earth.

• Daytime on Earth is when one side of the Earth faces the sun.

• Nighttime on Earth is when the side of Earth we are on faces away from the sun.

A Day on other Planets

• On Jupiter, a day

takes only 9 hours

and 50 minutes.

• On Venus, a day

last 243 Earth

days.

Earth’s revolution

• It takes the Earth 365

days (or rotations) to

travel or revolve

around the Sun once.

• One complete

revolution is called a

year.

A Year on other Planets

• On Mercury, one

revolution takes

only 88 days.

• On Neptune a

revolution takes

almost 165 Earth

years.

Earth’s orbit • The Earth’s orbit around the Sun in not a perfect

circle.

• The Earth’s orbit has an elliptical shape (oval).

• Because the Sun is closer to one side of the ellipse, the Earth’s distant from the Sun changes as it goes around the Sun.

•Perihelion- When Earth is closest to the sun

•Aphelion – When Earth is furthest from the

sun

Why do we have seasons?

• Seasons are not caused by how close the Earth is to the sun.

• In fact, the Earth is closest to the sun around January 3 and farthest away from the sun around July 4.

Why do we have seasons? (cont) • 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, and summer.

• The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun.

• The more daylight hours , the more time the ground has to be warmed up by the Sun.

ANGLE OF INSOLATION • The angle at which the sunlight hits the Earth is

called the Angle of insolation.

• The higher the angle the more heat that

location receives.

• The more heat the ground gets, the warmer the

air will be.

Why do we have Seasons? (cont) • Because the Earth’s tilt always points towards

Polaris and the Earth revolves around the

Sun, The Northern and Southern

Hemispheres receive different amount of light

throughout the year.

• When the North pole points towards the Sun,

it is Summer in the Northern Hemisphere and

Winter in the Southern Hemisphere..

• When the North pole points away from the

Sun, it is Summer in the Southern Hemisphere

and Winter in the Northern Hemisphere.

N

S

N

S

Why do we have seasons? (cont)

• Summer is warmer than winter (in each

hemisphere) because the Sun's rays hit the

Earth at a more direct angle during summer than

during winter

Why do we have seasons? (cont)

• Also the days are much longer than the

nights during the summer.

• During the winter, the Sun's rays hit the

Earth at an extreme angle, and the days are

very short.

Seasons…in a nut shell

The Movement of the Sun across the

sky during the change of seasons.

• Because the amount of sunlight areas

receive between Summer and Winter

changes, the Sun appears to travel north

and south throughout the year.

• This is an apparent movement – The Sun

isn’t moving but it is the revolution of the

Earth and its tilt that actually cause this

affect.

The Movement of the Sun across the

sky during the change of seasons.

• In the Northern Hemisphere, the Sun

travels furthest north during the Summer

months.(June)

• In the Northern Hemisphere, the Sun

travels furthest South during the Winter

months. (December)

• In the Southern Hemisphere it is opposite

Solstice

• Solstices occur twice a year, when the tilt

of the Earth's axis is oriented either

directly towards or away from the Sun,

causing the Sun to appear to reach its

northernmost and southernmost extremes.

• The days of Solstice has either

– The longest day of the year – about 16 hours

– Or the shortest day of the year – about 8

hours

Winter Solstice

• Winter solstice is the shortest day of the

year. In the Northern Hemisphere. It

occurs on December 21 and marks the

beginning of winter.

Winter Solstice • During the winter

solstice, the North Pole has a 24-hour night and the South Pole has a 24-hour day.

• Sunlight strikes the Earth most directly at the Tropic of Capricorn. 23 ½ degrees South Latitude.

•

Summer Solstice

• The Summer Solstice is the longest day of

the year. It occurs on June 21 and marks

the beginning of summer.

Summer Solstice • During the summer

solstice, the North Pole has a 24-hour Day and the South Pole has a 24-hour night.

• Sunlight strikes the Earth most directly at the Tropic of Cancer. 23 ½ degrees North Latitude.

•

Shadows during the Solstice • During the Winter Solstice, shadows are at

their longest.

• During the Summer Solstice, shadows are at

their shortest.

Equinoxes • An Equinox is when the northern and

southern hemispheres experience 12

hours of day and 12 hours of night.

• 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.

Equinox

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