Noor mahammad
Last Activity: 9 Years ago
The
Sun emits its peak power in the visible region, although integrating the entire emission power spectrum through all wavelengths shows that the Sun emits slightly more infrared than visible light.
[18] By definition, visible light is the part of the EM spectrum the
human eye is the most sensitive to. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underlie human vision and plant photosynthesis. The light that excites the human
visual system is a very small portion of the electromagnetic spectrum. A
rainbow shows the optical (visible) part of the electromagnetic spectrum; infrared (if it could be seen) would be located just beyond the red side of the rainbow with
ultraviolet appearing just beyond the violet end.
After UV come
X-rays, which, like the upper ranges of UV are also ionizing. However, due to their higher energies, X-rays can also interact with matter by means of the
Compton effect. Hard X-rays have shorter wavelengths than soft X-rays and as they can pass through many substances with little absorption, they can be used to 'see through' objects with 'thicknesses' less than that equivalent to a few meters of water. One notable use is diagnostic X-ray imaging in medicine (a process known as
radiography). X-rays are useful as probes in high-energy physics. In astronomy, the accretion disks around
neutron stars and
black holes emit X-rays, enabling studies of these phenomena. X-rays are also emitted by the
coronas of stars and are strongly emitted by some types of
nebulae. However,
X-ray telescopes must be placed outside the Earth's atmosphere to see astronomical X-rays, since the great depth of the
atmosphere of Earth is opaque to X-rays (with areal density of 1000 grams per cm
2), equivalent to 10 meters thickness of water.
[19] This is an amount sufficient to block almost all astronomical X-rays