SSeeaassoonnaall CChhaannggeess

Earth’s Tilt and RotationEarth’s Tilt and Rotation

Axis:Axis: The imaginary line that The imaginary line that

runs through the poles at runs through the poles at a tilt of 23 ½ degrees.a tilt of 23 ½ degrees.

The axis NEVER The axis NEVER changes its tilt direction. It changes its tilt direction. It remains at the same tilt remains at the same tilt as the earth revolves as the earth revolves around the sun.around the sun.

Because the earth spins Because the earth spins on this tilted axis all parts on this tilted axis all parts of the earth of the earth DO NOTDO NOT receive the same amount receive the same amount of sunlight.of sunlight.

Revolution:Revolution:

The movement of the The movement of the earth around the sun. earth around the sun. (Takes 365 days and (Takes 365 days and 6 hours) to make 1 6 hours) to make 1 revolution.revolution.

The revolution and The revolution and axis tilt determine the axis tilt determine the seasons of the year.seasons of the year.

March 21st/22ndMarch 21st/22nd the the sun is directly over sun is directly over the equator. the equator.

March 21st/22ndMarch 21st/22nd EquinoxEquinox

The sun is directly over the equator. The sun is directly over the equator. The number of daylight and night time The number of daylight and night time

hours are equal (12 and 12)hours are equal (12 and 12)This marks the beginning of Spring in the This marks the beginning of Spring in the

Northern Hemisphere and the Beginning Northern Hemisphere and the Beginning of Fall in the Southern Hemisphere. of Fall in the Southern Hemisphere.

September 23rdSeptember 23rd Equinox:Equinox:

The sun is directly over the equator again. The sun is directly over the equator again. This marks the beginning of This marks the beginning of FallFall in the in the

Northern HemisphereNorthern HemisphereAlso marks the beginning of Also marks the beginning of SpringSpring in the in the

Southern HemisphereSouthern Hemisphere. .

June 21st/22ndJune 21st/22nd SolsticeSolstice

The sun is directly over the The sun is directly over the Tropic of Tropic of CancerCancer (23 ½ degrees N) (23 ½ degrees N)

In the In the Northern HemisphereNorthern Hemisphere this is when this is when there is the there is the greatestgreatest amount of amount of daylightdaylight hours and marks the hours and marks the beginning of beginning of summersummer..

Southern HemisphereSouthern Hemisphere is where there is the is where there is the shortestshortest amount of daylight hours and amount of daylight hours and marks the marks the beginning of winterbeginning of winter..

December 22ndDecember 22nd Winter SolsticeWinter Solstice

The sun is directly over the The sun is directly over the Tropic of Tropic of CapricornCapricorn (23 ½ degrees S) (23 ½ degrees S)

Northern HemisphereNorthern Hemisphere has the has the leastleast amount of amount of daylightdaylight hours and marks the hours and marks the first day of winterfirst day of winter..

Southern HemisphereSouthern Hemisphere has the has the mostmost amount of amount of daylightdaylight hours and marks the hours and marks the first day of summerfirst day of summer..

The PolesThe Poles

North PoleNorth Pole

At the North Pole the At the North Pole the sun never sets sun never sets between March 20th–between March 20th–September 23rd. September 23rd.

There is constant There is constant daylight daylight 2424 hours a hours a day.day.

Fortress of SolitudeFortress of Solitude

South PoleSouth Pole

At the South Pole it is At the South Pole it is reversed. reversed.

September 23rd-September 23rd-March 20th the sun March 20th the sun never sets. (Meaning never sets. (Meaning Constant Daylight)Constant Daylight)

THE POLES (BOTH)THE POLES (BOTH)

For 6 months a year there is either For 6 months a year there is either constant darkness or constant daylight. constant darkness or constant daylight.

Midnight SunMidnight Sun is the term for constant is the term for constant daylight. daylight.

Effects of Midnight SunEffects of Midnight Sun

Constant sun or constant darkness alters Constant sun or constant darkness alters lifestyles in terms of:lifestyles in terms of:Food expensesFood expensesHuman internal functionsHuman internal functionsElectric billsElectric billsHuman mental state (State of mind)Human mental state (State of mind)