The Reason for the The Reason for the SeasonsSeasons

RotationRotation Earth Earth spinsspins on on axis axis (imaginary (imaginary

line through center of Earth line through center of Earth from North to South Pole)from North to South Pole)

Rotation is Rotation is counter clockwisecounter clockwise as seen from North Poleas seen from North Pole

Earth spins on its axis like a Earth spins on its axis like a toptop

Rotation - AxisRotation - Axis Earth Earth tilttilt = = 23.523.5°°

Axis currently Axis currently pointed at Polaris pointed at Polaris (the North Star)(the North Star)

Polaris

RotationRotation Earth rotates Earth rotates once once

every 24 hrsevery 24 hrs

The rotation The rotation causes causes day & nightday & night

Earth’s rotation Earth’s rotation causes causes celestial celestial objects to appear objects to appear to move from east to move from east to west in to west in Northern Northern Hemisphere Hemisphere

Night and Day MapNight and Day Map

Just Checking…Just Checking…

What does it mean when we say the What does it mean when we say the Earth rotates?Earth rotates?

How would you define or explain How would you define or explain the concept of Earth’s axis?the concept of Earth’s axis?

RevolutionRevolution Movement of one object Movement of one object aroundaround another another Earth revolves around SunEarth revolves around Sun

counterclockwise counterclockwise Earth’s orbit is almost Earth’s orbit is almost circular rather than oval circular rather than oval

shapedshaped but but is still referred to as anis still referred to as an elliptical orbit elliptical orbit 365 ¼ days to revolve once365 ¼ days to revolve once around the Sun (~ a around the Sun (~ a

year)year)

The imaginary line that runs The imaginary line that runs through the north and south poles through the north and south poles of the Earth is called the of the Earth is called the

A.A. EquatorEquator

B.B. AxisAxis

C.C. LongitudeLongitude

D.D. LatitudeLatitude

Decide weather each example is ofDecide weather each example is ofA. Rotation or B. RevolutionA. Rotation or B. Revolution

The Earth spinning on it’s axis.The Earth spinning on it’s axis. A baseball player running A baseball player running

around the infield.around the infield. Takes 1 yearTakes 1 year A top spinningA top spinning Causes day and night.Causes day and night. Takes 24 hoursTakes 24 hours The moon circling the EarthThe moon circling the Earth

Location and Distance in Location and Distance in OrbitOrbit

http://www.uwm.edu/~kahl/CoVis/Seasons/Handout available at

1. angle of Sun in the sky at a given time and latitude

2. number of hours of daylight at a given time and latitude.

Two Primary Reasons for the Two Primary Reasons for the Seasons (on Earth)Seasons (on Earth)

SeasonsSeasons

SeasonsSeasons Northern hemisphere tilts towards Northern hemisphere tilts towards

Sun = warmer (Summer)Sun = warmer (Summer)

SeasonsSeasons Northern hemisphere tilts away from Northern hemisphere tilts away from

Sun = cooler (winter)Sun = cooler (winter)

SeasonsSeasons In the Spring and the Fall, the tilt of the In the Spring and the Fall, the tilt of the

Earth is such that the spread of sunlight Earth is such that the spread of sunlight shines on the Earth approximately equallyshines on the Earth approximately equally

SeasonsSeasons

Southern hemisphere seasons Southern hemisphere seasons opposite Northern hemisphere opposite Northern hemisphere seasonsseasons

If its Winter here, then Australia If its Winter here, then Australia is having _?_.is having _?_.

SolsticesSolstices Occur twice yearly when the Sun is directly over Occur twice yearly when the Sun is directly over

“Tropics” (23.5“Tropics” (23.5°N and 23.5°S Latitude)°N and 23.5°S Latitude) winter solstice = shortest day of the year for winter solstice = shortest day of the year for

Northern Hemisphere (Sun directly over Northern Hemisphere (Sun directly over Tropic of Capricorn-Tropic of Capricorn-23.5°S23.5°S-at noon)-at noon)

Summer Solstice is the longest day of the Summer Solstice is the longest day of the year in the Northern Hemisphere (Sun year in the Northern Hemisphere (Sun directly over Tropic of Cancer-directly over Tropic of Cancer-23.523.5°N°N-at noon)-at noon)

EquinoxEquinox equal night & dayequal night & day Occurs Occurs twicetwice each each

yearyear Half-way between Half-way between

solsticessolstices noon sun directly noon sun directly

over equator over equator Sun will be at its Sun will be at its

highest point in our highest point in our sky at noon but sky at noon but never directly never directly overhead in Texas… overhead in Texas… why do you think why do you think this is true?this is true?

Your answer should refer to Godley, Your answer should refer to Godley, TX.TX. This occurs because the Earth’s This occurs because the Earth’s

axis is tilted as it moves around axis is tilted as it moves around the sun.the sun.

This occurs when the Northern This occurs when the Northern hemisphere is tilted towards the hemisphere is tilted towards the sun.sun.

This is when the length of day and This is when the length of day and night are equal.night are equal.

The shortest and longest days of The shortest and longest days of the year when the noon sun is the year when the noon sun is directly overhead at 23.5 degrees.directly overhead at 23.5 degrees.

This occurs when the Northern This occurs when the Northern hemisphere is tilted away from the hemisphere is tilted away from the sun.sun.

A.A. WinterWinter

B.B. SummerSummer

C.C. SolsticeSolstice

D.D. EquinoxEquinox

E.E. All of the All of the aboveabove

Based on this Night and Day Map…Based on this Night and Day Map…

• What season do you think it is in Godley?What season do you think it is in Godley?

• What time do you think it is in Godley?What time do you think it is in Godley?