The electromagnetic radiation and particles (electrons, protons, alpha particles, and rarer heavy atomic nuclei) emitted by the Sun. The electromagnetic radiation covers a wavelength range from x-rays to radio waves, that is, from about 0.01 nanometer to 30 km. The annual mean irradiance at Earth, integrated over the whole spectrum, amounts to 1365 W · m−2, and 99% of its energy is carried by radiation with wavelengths between 278 and 4600 nm, with the maximum at 472 nm. See also Electromagnetic radiation; Solar constant.
The Sun also emits a continuous stream of particles, the solar wind, which originates in coronal holes and the upper corona. Explosive events on the Sun, the solar flares and coronal mass ejections, emit particles that are much more energetic and numerous than those of the solar wind. Solar flares are produced by the most powerful explosions, releasing energies of up to 1025 joules in 100–1000 s and high-speed electrons that emit intense radiation at radio and x-ray wavelengths. They also produce nuclear reactions in the solar atmosphere with the emission of gamma rays and of neutrons that move nearly at the speed of light. Coronal mass ejections expand away from the Sun at speeds of hundreds of kilometers per second, becoming larger than the Sun and removing up to 5 × 1013 kg of coronal material. Both events are believed to be ignited by the reconnection of magnetic fields. If the emitted particles reach the Earth, they give rise to the aurora at high latitudes, and they can damage satellites, endanger humans in space, and on the Earth disturb telecommunications and even disrupt power systems. See also Aurora; Cosmic rays; Ionosphere; Magnetosphere; Solar wind; Sun.
The emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity.
The soldering process.
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