the most plentiful comprising about 44 percent of the solar output. Seven percent
of solar energy is invisible ultraviolet energy mainly absorbed by the atmosphere
and 11 percent is thermal infrared energy. About a third of the energy (37 percent)
is in the near infrared portion of the spectrum and not sensible by humans. The sun
also emits microwaves, television waves, and radio waves and these corporately
account for less than 1 percent of the solar energy output. Significant amounts of
solar energy are transformed into thermal infrared energy on interaction with
Earth’s atmosphere and surface, and it isthis transformed energy that is largely
responsible for heating of the planet (seeHeating and cooling).
The penetration of solar energy deep into the atmosphere and onto Earth’s sur-
face directly forces winds to blow andocean currentsto flow. That is, solar energy
forces the circulation systems of the planet. When examiningseasons,itisclear
that the systematic changes in the latitudinal receipt of solar energy as caused by
the revolution of the Earth about the sun make for systematic variations in the
amount of air and water circulating in any geographic region.
Of considerable concern is the increasingamount of ultraviolet radiation reaching
Earth’s surface. In recent years the ozone of the stratosphere has been eroding, particu-
larly in the far southerly latitudes. Unmitigated solar ultraviolet energy is fatal to land
life,andanyincreaseinpresentamountsreachingEarth’ssurfacewillbringanarray
of unwanted effects. These include increased incidence of human skin cancer, DNA
modification in plants and animals, and breakdown of exposed metals and fabrics.
Solar energy has been used in myriad ways to aid human activity. Drying foods,
passive heating strategies for traditional housing forms, and distillation of salt
water to fresh water are simple historic examples of our conscious manipulation
of energy from our local star. Modern humans have begun to use large amounts
of solar energy to make electricity and warm water for household purposes. Such
uses can only grow as Earth’s fossil fuels become more expensive.Spatial Inequality
A spatial differentiation of abundance of any measurable quality or characteristic.
No geographical feature is evenly distributed across anylandscapeof theEarth
except at a very small scale, so every spatial characteristic ismarkedbyspatial
inequality to some degree. Spatial inequality is primarily of concern to scholars
who study thegeography of economic development, and is related to the concept
ofsegregation, a condition in which spatial inequality is established in an urban
environment on the basis of race or other considerations and is reflected in the
social distancebetween groups. Spatial inequality is often the motivating factor316 Spatial Inequality