Unit 2

World Climate Patterns

Earth-Sun Relations

Revolution Vs. ROTATION.

• The earth rotates (spins) on its axis…• In a Counter-clockwise direction…• which takes 24 hours and results in day and night.

Night – Away from the sun

Day – Exposed to the sun

REVOLUTION Vs. rotation.• The earth revolves (orbits)

around the sun

• Again in a counter-clockwise direction…

• it takes 365 days and results in seasons.

• At NO point is the Earth closer to the sun during its orbit ….

• Temperature variation is in NO WAY influenced by distance from the sun.

•http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.swf

3D image of the Earth’s Revolution…

Tilt of the Earth

• The earth is tilted on its axis @ 23.5o

• At different times of the year, the North (or South) is pointed towards the sun, while other times pointed away from the sun.

• Causes daylight to be longer or shorter.

• Contributes to the seasons as well.

Day vs Night & Length of day (daylight!)

• Rotation on the axis causes day and night

• Tilt on axis causes length of day to be longer or shorter.

• When hemisphere is pointed towards the sun…

• that hemisphere receives more direct, intense heat radiation AND

• More hours of exposure to the sun

• Giving that hemisphere longer days AND

• Warmer temperatures (Summer!!)

Equal Day and Night…BUT…

Differences in Temperatures!? Why?

Intensity and Duration!!

EquinoxEquinox && SOLSTICESOLSTICESOLSTICESOLSTICE

From Latin for From Latin for sun sun stands stillstands still

Winter & SummerWinter & Summer which are the which are the shortest & longest shortest & longest daysdays

Sun is directly over Sun is directly over headhead @ 12 noon on @ 12 noon on 23.523.5oo (North or (North or South.)South.)

NorthernNorthern hemisphere hemisphere pointed pointed TOWARDSTOWARDS the the sun in sun in SummerSummer

NorthernNorthern hemisphere hemisphere pointed pointed AWAYAWAY from the from the sun in sun in WinterWinter

Occurs Occurs Dec 21 & June 21Dec 21 & June 21

EQUINOXEQUINOX && solsticesolsticeEQUINOXEQUINOX

From Latin for From Latin for equal equal day & night.day & night.

Sun is directly Sun is directly overheadoverhead @ 12 noon @ 12 noon on the on the equator.equator.

EqualEqual length of night length of night & day everywhere on & day everywhere on earthearth

NeitherNeither the northern the northern hemisphere hemisphere NORNOR the the southern hemisphere are southern hemisphere are pointed towards or away pointed towards or away from the sunfrom the sun

In the North, occurs In the North, occurs Sept. Sept. 21 (Autumnal/Fall)21 (Autumnal/Fall) & & March 21(Vernal/Spring)March 21(Vernal/Spring)

Season changesSeasonal changes are all driven by changes in:

The tilt of the earth on its axis ANDThe position of the earth in its revolution around the sun

NOTE: These will ultimately determine:the amount of available sunlight (called day length or photoperiod) the sun's intensity (related to the angle at which it strikes the Earth).Warmer vs cooler

Seasons Summary – SUMMER in the NORTH!!

•June 21st or 22nd.

•North = Summer

•More sun hours

•More direct sun

•Noon Sun 900 @ Tropic of Cancer

•South = Winter

•Less sun hours

•Less direct sun

A

Seasons Summary – FALL / AUTUMN

in the NORTH

•September 21st

•North = Fall

•12 hrs day & 12 hrs night

•Noon Sun 900 @ Equator

•South = SpringB

A

B

A

Seasons SummaryWINTER in the NORTH

•Dec 21st

•North = Winter

•Less sun hours

•Less direct sun

•South = Summer

•More sun hours

•More direct sun

•Noon Sun 900 @ Tropic of Capricorn

C

Seasons SummarySPRING in the NORTH

•March 21st

•North = Spring

•12 hrs day & 12 hrs night

•Noon Sun 900 @ Equator

•South = Fall

B

AC

D

Seasons SummaryBack to Summer AGAIN!

B

AC

D

NORTH

NORTHSOUTH

SOUTH

SEASONS??? DATE???

LENGTH of DAY??? EQUINOX/SOLSTICE?

Where are these seasons experienced?

Northern Hemisphere or Southern Hemisphere?

How do you know?

Southern

What season is it in the Northern Hemisphere?N

1. Canada… when it’s the vernal equinox in South Africa?

2. Argentina… when it is winter in Norway?

3. Greenland… when it is Fall in Mongolia?

4. Mexico… when it is summer in south Australia?

5. Iceland… when its autumnal equinox in New Zealand?

What season is

it in …

Know seasons are reversed in Northern & Southern Hemispheres

Date North South

June

Sept.

Dec.

March

Seasons animated:Sun’s Angle and Intensity.

• http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.swf

End of Slide Show!