Scientific American - USA (2021-03)

76 Scientific American, March 2021

SOURCE: NOA A SOLAR CALCULATOR

GRAPHIC SCIENCE

Text by Mark Fischetti | Graphic by Jen Christiansen and Mapping Specialists

Daylight’s

Uneven

March

Sunlight changes

unequally all year long

People who live in the midlatitudes en ­

joy maximum daylight on the summer

solstice and put up with maximum dark­

ness on the winter solstice. Be tween the

two extremes, sunlight in creases or de ­

creases each day, but the rate of change

is not steady. It is least in midsummer

and midwinter and greatest around the

spring and fall equinoxes. The biggest

shifts occur at very high latitude: Just

before the period of total darkness (or

just after total darkness), the sun is bare­

ly above the horizon around solar noon,

when the solar elevation changes very

slowly, resulting in a large daily differ­

ence in daylight minutes lost (or gained).

People who live along the equator see no

change; they experience a steady 12 hours

of day and night throughout the year.

No sunlight 12 hours 24 hours

Sunlight gained

Sunlight lost

(^0) 5 minutes
10
15
Jan. 19, 2021
Time
Feb. 18Mar. 20Apr. 20May 20 July 22 Aug. 22 Oct. 22Nov. 21
Equinox
June 20
Solstice
Sept. 22
Equinox
Dec. 21
Solstice
30° N
15° N
Equator
45 ° N
60 ° N
70 ° N
15° S
30° S
45 ° S
60 ° S
70 ° S
At 45 degrees north latitude—Bangor, Maine;
Bordeaux, France; Toyotomi, Japan—the daily rate
of sunlight change is almost exactly two minutes in
January, May, July and November and more than
three minutes in March and September.
Bars show daily hours of sunlight and darkness
for each latitude.
Clocks show minutes
of sunlight gained
or lost compared
with the previous day.
Equator
Equator
15° North
15° South
30° N
30° S
45° S
60° S
70° S
45° N
60° N
70° N