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Solar and Heliospheric Observatory

Large solar flare recorded by EIT304 instrument. . . Courtesy SOHO(ESA&NASA)
The Solar and Heliospheric Observatory (SOHO) is a spacecraft launched in 1995 to study the sun. It is a joint project of the European Space Agency (ESA) and NASA.

The 610kg SOHO spacecraft orbits the L1 Lagrange point, the point between the Earth and the Sun where the Earth's gravity exactly counterbalances the Sun's, which is about 1.5 million kilometres from the Earth. Although sometimes described as being at L1, the SOHO satellite is not exactly at L1 as this would make communication difficult and is not a stable orbit. Rather it orbits L1 once every six months, while L1 itself orbits the sun every 12 months as a direct consequence of the motion of the Earth. This keeps SOHO at a good position for communication with Earth at all times.

In normal operation the spacecraft transmits a continuous 200Kb/s data stream of photographs and other measurements via the NASA deep space network of receiving stations. SOHO's data about solar activity are used to predict solar flares, so electrical grids and satellites can be protected from their damaging effects.

SOHO contains twelve main instruments, each capable of independently observing the sun or parts of the sun. These are:

The observations from all of these instruments are archived to the World Wide Web and tools are provided for public access to them.

Some of these observations can be formatted as images, many of which are also readily available on the internet, see the official website. Others such as spectra and measurements of particles in the solar wind do not lend themselves so readily to this. These images range in wavelength or frequency from optical (H) to extreme ultraviolet (UV). Images taken partly or exclusively with non-visible wavelengths are shown on the SOHO page and elsewhere in false color.

See also solar astronomy

External links