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Diagram showing displacement of the Sun's image at sunrise and sunset Comparison of inferior and superior mirages due to differing air refractive indices, n. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. [1]
Pressure modes are in essence standing sound waves. The dominant restoring force is the pressure (rather than buoyancy), hence the name. All the solar oscillations that are used for inferences about the interior are p modes, with frequencies between about 1 and 5 millihertz and angular degrees ranging from zero (purely radial motion) to order .
The ionosphere is a layer of partially ionized gases high above the majority of the Earth's atmosphere; these gases are ionized by cosmic rays originating on the sun. When radio waves travel into this zone, which commences about 80 kilometers above the earth, they experience diffraction in a manner similar to the visible light phenomenon described above. [1]
If the extraterrestrial solar radiation is 1,367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1,050 W/m 2, but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1,120 W/m 2. [6]
The visible spectrum, approximately 380 to 740 nanometers (nm), [1] shows the atmospheric water absorption band and the solar Fraunhofer lines. The blue sky spectrum contains light at all visible wavelengths with a broad maximum around 450–485 nm, the wavelengths of the color blue.
A radio wave can be reflected in the solar atmosphere when it encounters a region of particularly high density compared to where it was produced, and such reflections can occur many times before a radio wave escapes the atmosphere. This process of many successive reflections is called scattering, and it has many important consequences. [47]
The optical atmospheric window is the optical portion of the electromagnetic spectrum that passes through the Earth's atmosphere, excluding its infrared part; [10] although, as mentioned before, the optical spectrum also includes the IR spectrum and thus the optical window could include the infrared window (8 – 14 μm), the latter is ...
The windows provide direct channels for Earth's surface to receive electromagnetic energy from the Sun, and for thermal radiation from the surface to leave to space. [3] Atmospheric windows are useful for astronomy , remote sensing , telecommunications and other science and technology applications.