World:Radiation
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Radiation
The Earth is protected from cosmic radiation by a magnetic field generated by its convecting, molten core. This hot, radioactive "geodynamo" is slowly cooling, and will in a long-term perspective cause the magnetic field and the protective "shield" it forms to fade (and the magnetic poles to reverse -- not for the first time).
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A decreased magnetic field will expose the Earth to harmful solar and cosmic radiation:
Solar radiation
Source: http://en.wikipedia.org/wiki/Solar_radiation
Solar radiation is radiant energy emitted by the Sun, particularly electromagnetic energy. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum. The other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum. The portion of this ultraviolet radiation that is not absorbed by the atmosphere produces a suntan or a sunburn on people who have been in sunlight for extended periods of time.
Solar flare
Source: http://en.wikipedia.org/wiki/Solar_flare
A solar flare is a violent explosion in the Suns atmosphere with an energy equivalent to tens of millions of hydrogen bombs. Solar flares take place in the solar corona and chromosphere, heating plasma to tens of millions of kelvins and accelerating the resulting electrons, protons and heavier ions to near the speed of light. They produce electromagnetic radiation across the electromagnetic spectrum at all wavelengths from long-wave radio to the shortest wavelength Gamma rays. Most flares occur around sunspots, where intense magnetic fields emerge from the Suns surface into the corona. The energy efficiency associated with solar flares may take several hours or even days to build up, but most flares take only a matter of minutes to release their energy.
Solar flares were first observed on the Sun in 1859. Stellar flares have also been observed on a variety of other stars.
The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly "active" to less than one each week when the Sun is "quiet". Solar activity varies with an 11-year cycle (the solar cycle). At the peak of the cycle there are typically more sunspots on the Sun, and hence more solar flares.
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Hazards
Solar flares and associated Coronal Mass Ejections (CMEs) strongly influence our local space weather. They produce streams of highly energetic particles in the solar wind and the Earths magnetosphere that can present radiation hazards to spacecraft and astronauts. The soft X-ray flux of X class flares increases the ionisation of the upper atmosphere, which can interfere with short-wave radio communication, and can increase the drag on low orbiting satellites, leading to orbital decay. Energetic particles in the magnetosphere contribute to the aurora borealis and aurora australis.
Solar flares release a cascade of high energy particles known as a proton storm. Protons can pass through the human body, doing biochemical damage. Most proton storms take two or more hours from the time of visual detection to reach Earth. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured, taking only 15 minutes after observation to reach Earth.
Cosmic radiation
Source: http://en.wikipedia.org/wiki/Cosmic_radiation
In astrophysics, cosmic rays are radiation consisting of energetic particles originating beyond the Earth that impinge on the Earths atmosphere. Cosmic rays are composed mainly of bare nuclei, roughly 87 alpha particles (helium nuclei) and most of the rest being made up of heavier atomic nuclei with relative abundances comparable to those found in the Sun. Electrons, gamma rays, and very high-energy neutrinos also make up a much smaller fraction of the cosmic radiation.
High speed cosmic rays can damage DNA, increasing the risk of cancer, cataracts, neurological disorders, and non-cancer mortality risks.
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-- Main.World:Geir_thomas_andersen - 16 Sep 2006
