Celestron CG-4 User Manual download pdf (Page 10)

GENERAL INFORMATION

Within this spectral range the earth is able to maintain an equilibrium

temperature by losing a certain quantity of heat gained each day from

the sun.

The sun radiates approximately as a blackbody at an equivalent

temperature of nearly 5770K. Almost 99% of its emitted energy are

contained in wavelengths less than 4µm and are called short-wave

radiation. The equivalent radiant temperature of the Earth’s surface is

about 275K. More than 99% of this energy is emitted at wavelengths

more than 3 µm and is called long-wave, thermal, or infrared radiation.

Downward long wave radiation is a result of atmospheric re-emission.

Re-emission is the reversible effect of absorption of earthly emitted

long wave radiation by chemical elements like water (H

O), Oxygen

), Ozone (O

), Carbon dioxide (CO

) etc. These elements are the

main emitters of long wave radiation in the atmosphere.

The remaining unabsorbed portion of the earth’s radiation escapes

into the outer space. Under clear skies an object can be cooled below

ambient air temperature by radiative heat loss to the sky. Observing

the earth from outer space, a blackbody is seen in a range of 8 to 14

µm with a temperature of 14 °C and outside this wavelength range a

blackbody of -60 °C. Under clear sky conditions in a reverse direction,

outer space can be observed in the same spectral range. The long

wave radiation exchange mainly occurs in the spectral range of 8 to

14µm. In this range the pyrgeometer also loses its thermal energy

upward.

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 63 64

No comments

Celestron CG-4 User Manual Page 10