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SOHO is a joint space mission of the European Space Agency (ESA) and NASA, and is designed to study the internal structure of the Sun, its extensive outer atmosphere and the origin of the solar wind, the stream of highly ionized gas that blows continuously through the solar system.
By operating around a point 1.5 million kms sunward of the Earth, at the point where the Sun's gravity balances the Earth's, SOHO provides scientists with their first long term uninterrupted view of Sun.
There are five instruments onboard SOHO to observe the Sun:
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EIT (Extreme Ultraviolet Imaging Telescope) - This highlights gas at between 80,000 to 2 million degrees and provides daily weather maps of the Sun.
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CDS (Coronal Diagnostics Spectrometer) - Scans small areas of the Sun, measuring intensities over a wide range of sharply defined wavelengths - has proved valuable for deducing temperatures and densities of the gas.
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SUMER (Solar Ultraviolet Measurements of Emitted Radiation) - Same process as CDS, but excels in measuring velocities of gas streams and detecting previously unknown ultraviolet emissions.
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UVCS (Ultraviolet Coronagraph Spectrometer) - this masks out the solar disk itself, allowing analysis of ultraviolet emissions from the corona, from 350,000 to 14 million kms above the visible surface. It gauges the energy of atoms leaving the Sun in the solar wind.
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LASCO (Large Angle Spectrometric Coronagraph) - This observes visible light from the corona using three masked telescopes, covering a range of 140,000 kms to 20 million kms from the Sun's surface. Provides spectacular images of Coronal Mass Ejections (CMEs).
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