WHY DO THE LENGTHS OF DAY AND NIGHT CHANGE WITH THE SEASON AND LATITUDE?

WHY DO THE LENGTHS OF DAY AND NIGHT CHANGE WITH THE SEASON

AND LATITUDE?

SUN

March 21

December 21

N

s

Equator

Antarctic C.

Cancer

Arctic C.

Capricorn

June 21

September 21

66.5°N

23.5°N

66.5°S

23.5°S

0°

VIEW FROM OVER THESUN LOOKING DOWNON EARTH’S NORTH

POLE.

North Pole(Constant tilt)

SUN

March 21

December 21June 21

September 21VIEW FROM OVER THESUN LOOKING DOWNON EARTH’S NORTH

POLE.North Pole

(Constant tilt)

Half of Earth indarkness

Circle of IlluminationDay/Night

SUN

March 21

December 21 June 21

September 21

SUN

March & September 21

June 21December 21

N

s

Equator

Antarctic C.

Cancer

Arctic C.

Capricorn All places in the world spend equal lengthsof time in the dark (night) and lighted (day).

EQUINOXES

SUN

March 21

December 21

N

s

June 21

September 21

Places in northern hemisphere spend more than half a dayin darkness. Proportion of rotation in darkness increases to the Arctic Circle

Places in southern hemisphere spend more than half a dayin light. Proportion of rotation in daylight increases to the Antarctic Circle

December 21

Antarctic Circle

Arctic Circle

SUN

June 21

December 21

March 21

September 21

N

s

Places in southern hemisphere spend more than half a dayin darkness. Proportion of rotation in darkness increases to the Antarctic Circle.

Places in northern hemisphere spend more than half a dayin light. Proportion of rotation in daylight increases to the Arctic Circle.

Arctic Circle

Antarctic Circle

SUN

March & September 21

December 21

N

s

Equator

Antarctic C.

CancerArctic C.

Capricorn

N

s

June 21N

s

September 21

LatitudeDegrees

North

June SolsticeHours ofDaylight

March/SeptemberEquinoxHours ofDaylight

December SolsticeHours ofDaylight

90 6 months 12hr 0 hr

80 4 months 12hr 0 hr

70 2 months 12hr 0 hr

66.5 24 hr 12hr 0 hr

50 16 hr 12hr 8 hr

40 15 hr 12hr 9 hr

30 14 hr 12hr 10 hr

20 13 hr 12hr 11 hr

10 12.5hr 12hr 11.5 hr

0 12hr 12hr 12 hr

N

s

N

s

Equator

Antarctic C.

CancerArctic C.

Capricorn

N

s

THE BOTTOM LINE

THE BOTTOM LINE

• 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season.

LatitudeDegrees

North

June SolsticeHours ofDaylight

March/SeptemberEquinoxHours ofDaylight

December SolsticeHours ofDaylight

90 6 months 12hr 0 hr

80 4 months 12hr 0 hr

70 2 months 12hr 0 hr

66.5 24 hr 12hr 0 hr

50 16 hr 12hr 8 hr

40 15 hr 12hr 9 hr

30 14 hr 12hr 10 hr

20 13 hr 12hr 11 hr

10 12.5hr 12hr 11.5 hr

0 12hr 12hr 12 hr

N

s

N

s

Equator

Antarctic C.

CancerArctic C.

Capricorn

N

s

THE BOTTOM LINE

• 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season.

• 2. On March 21 and September 21 (Equinoxes) all places in the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude.

LatitudeDegrees

North

June SolsticeHours ofDaylight

March/SeptemberEquinoxHours ofDaylight

December SolsticeHours ofDaylight

90 6 months 12hr 0 hr

80 4 months 12hr 0 hr

70 2 months 12hr 0 hr

66.5 24 hr 12hr 0 hr

50 16 hr 12hr 8 hr

40 15 hr 12hr 9 hr

30 14 hr 12hr 10 hr

20 13 hr 12hr 11 hr

10 12.5hr 12hr 11.5 hr

0 12hr 12hr 12 hr

N

s

N

s

Equator

Antarctic C.

CancerArctic C.

Capricorn

N

s

THE BOTTOM LINE

• 1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season.

• 2. On March 21 and September 21 (Equinoxes) all places in the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude.

• 3. All places lying north of the Arctic Circle (66.5°N) or south of the Antarctic Circle (66.5°S) will experience at least one day of total darkness and one of total daylight.

LatitudeDegrees

North

June SolsticeHours ofDaylight

March/SeptemberEquinoxHours ofDaylight

December SolsticeHours ofDaylight

90 6 months 12hr 0 hr

80 4 months 12hr 0 hr

70 2 months 12hr 0 hr

66.5 24 hr 12hr 0 hr

50 16 hr 12hr 8 hr

40 15 hr 12hr 9 hr

30 14 hr 12hr 10 hr

20 13 hr 12hr 11 hr

10 12.5hr 12hr 11.5 hr

0 12hr 12hr 12 hr

N

s

N

s

Equator

Antarctic C.

CancerArctic C.

Capricorn

N

s

THE BOTTOM LINE• 1. All places at the equator receive 12hrs of daylight and

12hrs of darkness regardless of the season.• 2. On March 21 and September 21 (Equinoxes) all places in

the world receive 12 hrs of daylight and 12hrs of darkness regardless of their latitude.

• 3. All places lying north of the Arctic Circle (66.5°N) or south of the Antarctic Circle (66.5°S) will experience at least one day of total darkness and one of total daylight.

• 4. As one moves geographic position from the equator to the poles the differences in summer and winter lengths of day and night become more extreme.

Fairbanks, Alaska,Midday, December 21.

Spitzbergen, Norway,Midnight, June 21.

Sun Rise - Sun Set, DaylightGainesville, Florida, 29°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D

Sun Rise - Sun Set, DaylightGainesville, Florida, 29°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D

Sun Rise - Sun Set, DaylightGainesville, Florida, 29°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D

Sun Rise - Sun Set, DaylightGainesville, Florida, 29°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D

Sun Rise - Sun Set, DaylightSan José, Costa Rica, 10°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D

Sun Rise - Sun Set, DaylightSouthampton, England, 51°N

DarknessHours of Daylight

Julian Day0 30 60 90 120 150 180 210 240 270 300 330 360

Tim

e of

Day

(24h

r. cl

ock)

and

Day

light

(hrs

)

0

4

8

12

16

20

24

0

4

8

12

16

20

24J F M A M J J A S O N D