Background Info

A NASA satellite instrument, CERES, took these images in 2004 and 2005. The images are measurements of the Earth’s albedo—the amount of solar radiation reflected from Earth back into space. 
 
The CERES images show a radical difference in albedo between the Northern and Southern Hemispheres, as well as between the December and June solstices. The Southern Hemisphere reflects a tremendous amount of radiation during the December solstice (top image), while the Northern Hemisphere reflects more radiation in June.
 
Instructional Ideas
 
Consult National Geography Standard 7.2 (4th grade): The physical processes that shape the patterns of Earth's surface. Earth-Sun relationships affect conditions on Earth.
Discuss the relationship between the position of the Earth in its orbit around the sun and changes experienced on Earth:
• temperature
• light
• different impacts of solar radiation on land and water
 
Questions in the "Questions" tab explore some ways solar radiation differs in the Northern and Southern Hemispheres on the solstices.

Questions

1. 

Why do you think the Southern Hemisphere reflects so much more solar radiation than the Northern Hemisphere during the December solstice? This illustration might help you.

 

Show Answer

The Southern Hemisphere simply has more sunlight to reflect! The winter solstice is the longest day of the year in the Southern Hemisphere. This means it experiences more sunlight on this day than any other. In fact, in parts of Antarctica, there is no nighttime at all during this part of the season!

 

The December solstice is when the Southern Hemisphere receives the maximum intensity of the sun’s rays. The angle of sunlight is greater in the Southern Hemisphere during the winter.

 

During the June solstice, the opposite is true. The Northern Hemisphere receives the maximum intensity of the sun’s rays, while the angle of sunlight decreases in the Southern Hemisphere.

2. 

When the polar region of the Northern Hemisphere is reflecting the maximum amount of sunlight (the June solstice), it doesn’t reflect nearly as much light as the polar region of the Southern Hemisphere when it reflects its maximum amount of sunlight (December solstice). Why do you think the Southern Hemisphere reflects more solar radiation?

Show Answer

The polar region of the Southern Hemisphere is dominated by land—the continent of Antarctica. Even during the “warm” season (the December solstice), Antarctica is covered by a thick ice sheet. Ice reflects light beautifully.

 

The polar region of the Northern Hemisphere is dominated by the ocean. During the June solstice, sea ice on the Arctic Ocean is at its minimum. Liquid water is better at absorbing, not reflecting, solar radiation.

3. 

The 2013 December solstice will occur on Saturday, December 21. Will it be the shortest or longest day of the year?

Show Answer

That depends on whether you’re in the Southern or Northern Hemisphere! It will be the shortest day of the year north of the Equator—very little sunlight will be reflected back into space. It will be the longest day of the year south of the Equator—summertime.

Fast Facts

  • Solar radiation measured by CERES includes not just the visible spectrum of light, but ultraviolet and infrared—wavelengths too short (ultraviolet) or too long (infrared) for the human eye to see. 
  • Clouds do most of the reflecting in these NASA images. (In fact, CERES, the instrument responsible for these images, stands for Clouds and Earth’s Radiant Energy System.)

  • According to CERES, the amount of solar energy received at the North Pole is 30% higher during the summer solstice than the amount of solar energy received at the Equator.

  • Scientists measure solar radiation in Watts per square meter (W/m2). Calculating this measurement involves some pretty sophisticated—but pretty reliable—math. Check it out here.

For Further Exploration

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

albedo

Noun

scientific measurement of the amount of sunlight that is reflected by a surface.

hemisphere

Noun

half of a sphere, or ball-shaped object.

Encyclopedic Entry: hemisphere

measurement

Noun

process of determining length, width, mass (weight), volume, distance or some other quality or size.

NASA

Noun

(acronym for National Aeronautics and Space Administration) U.S. agency responsible for space research and systems.

reflect

Verb

to rebound or return light from a surface.

satellite

Noun

object that orbits around something else. Satellites can be natural, like moons, or made by people.

season

Noun

period of the year distinguished by special climatic conditions.

Encyclopedic Entry: season

solar radiation

Noun

light and heat from the sun.

solstice

Noun

astronomical event that occurs twice a year, when the sun appears directly overhead to observers at the Tropic of Cancer or the Tropic of Capricorn.

Encyclopedic Entry: solstice

sunlight

Noun

visible radiation from the sun.

tremendous

Adjective

very large or important.

Credits

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Writer

Caryl-Sue, National Geographic Society

Editor

Sean P. O'Connor, National Geographic Society

Producer

Caryl-Sue, National Geographic Society

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