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

2. September 21 VIEW FROM OVER THE SUN LOOKING DOWN North Pole
ON EARTH’S NORTH
POLE.
North Pole
(Constant tilt)
SUN
December 21
June 21 N
66.5°N
March 21
Arctic C.
Cancer
23.5°N
Equator 0°
Capricorn
23.5°S
Antarctic C.
66.5°S s

3. Circle of Illumination
VIEW FROM OVER THE
SUN LOOKING DOWN
ON EARTH’S NORTH
POLE.
September 21
North Pole
(Constant tilt)
SUN
December 21
June 21
Circle of Illumination
Day/Night
March 21
Half of Earth in
darkness

4. September 21
SUN
June 21
December 21
March 21

5. EQUINOXES SUN December 21 June 21 March & September 21
Arctic C.
Cancer
March & September 21
Equator
Capricorn
All places in the world spend equal lengths
of time in the dark (night) and lighted (day).
EQUINOXES
Antarctic C. s

6. s September 21 December 21 SUN June 21 March 21
Places in northern hemisphere spend more than half a day
in darkness. Proportion of rotation in darkness increases to the Arctic Circle N s
December 21
Arctic Circle
Places in southern hemisphere spend more than half a day
in light. Proportion of rotation in daylight increases to the Antarctic Circle
Antarctic Circle

7. Places in northern hemisphere spend more than half a day
September 21
SUN
December 21
March 21
Places in northern hemisphere spend more than half a day
in light. Proportion of rotation in daylight increases to the Arctic Circle. N s
June 21
Arctic Circle
Places in southern hemisphere spend more than half a day
in darkness. Proportion of rotation in darkness increases to the Antarctic Circle.
Antarctic Circle

8. s September 21 SUN December 21 June 21 s s March & September 21 N N N
Arctic C.
Cancer
Equator
Capricorn
Antarctic C. s
March & September 21

9. s s s N N N Latitude Degrees North June Solstice Hours of Daylight
Arctic C.
Cancer
Equator
Capricorn
Antarctic C. s s s
Latitude
Degrees
North
June Solstice
Hours of
Daylight
March/September
Equinox
December Solstice 90
6 months
12hr
0 hr 80
4 months 70
2 months
66.5
24 hr 50
16 hr
8 hr 40
15 hr
9 hr 30
14 hr
10 hr 20
13 hr
11 hr 10
12.5hr
11.5 hr
12 hr

10. THE BOTTOM LINE

11. THE BOTTOM LINE
1. All places at the equator receive 12hrs of daylight and 12hrs of darkness regardless of the season.

12. s s s N N N Latitude Degrees North June Solstice Hours of Daylight
Arctic C.
Cancer
Equator
Capricorn
Antarctic C. s s s
Latitude
Degrees
North
June Solstice
Hours of
Daylight
March/September
Equinox
December Solstice 90
6 months
12hr
0 hr 80
4 months 70
2 months
66.5
24 hr 50
16 hr
8 hr 40
15 hr
9 hr 30
14 hr
10 hr 20
13 hr
11 hr 10
12.5hr
11.5 hr
12 hr

13. 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.

14. s s s N N N Latitude Degrees North June Solstice Hours of Daylight
Arctic C.
Cancer
Equator
Capricorn
Antarctic C. s s s
Latitude
Degrees
North
June Solstice
Hours of
Daylight
March/September
Equinox
December Solstice 90
6 months
12hr
0 hr 80
4 months 70
2 months
66.5
24 hr 50
16 hr
8 hr 40
15 hr
9 hr 30
14 hr
10 hr 20
13 hr
11 hr 10
12.5hr
11.5 hr
12 hr

15. 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.

16. s s s N N N Latitude Degrees North June Solstice Hours of Daylight
Arctic C.
Cancer
Equator
Capricorn
Antarctic C. s s s
Latitude
Degrees
North
June Solstice
Hours of
Daylight
March/September
Equinox
December Solstice 90
6 months
12hr
0 hr 80
4 months 70
2 months
66.5
24 hr 50
16 hr
8 hr 40
15 hr
9 hr 30
14 hr
10 hr 20
13 hr
11 hr 10
12.5hr
11.5 hr
12 hr

17. 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.

18. Spitzbergen, Norway,
Midnight, June 21.
Fairbanks, Alaska,
Midday, December 21.