The Solar and Heliospheric Observatory or SOHO for short is a cooperative joint effort by the European Space Agency (ESA) and the U. S. National Aeronautics and Space Administration (NASA). The main mission of this project is to study the internal structure of the Sun, its extensive upper atmosphere, as well as to determine the origin and characteristics of the solar wind.
The SOHO spacecraft was launched on December 2, 1995 where then it was directed to go about 930,000 miles sunward from the Earth to the L1 or the Lagrangian point. This "Lagrangian" point is a place between the Sun and the Earth where the gravity pulls of both masses stabilize the spacecraft enough to achieve a state of gravitational equilibrium between the two masses. At this point, the spacecraft then established its own "halo-like" orbit in space but continued to also orbit about the Sun in the same orbital path as the Earth. Once SOHO's "halo-like" orbit was established, the spacecraft was then ready to open its payload bay doors and begin its probing of the Sun with its wide array of scientific instruments.
All instruments aboard the SOHO spacecraft fall under one of the following headings based on what area of the Sun it is suppose to observe and measure: the solar interior, the solar atmosphere, or the solar wind. The solar interior instruments such as GOLF (Global Oscillations at Low Frequencies) and VIRGO (Variability of Solar Irradiance and Gravity Oscillations) both perform oscillation measurements of the full solar disk which obtains information concerning the solar nucleus. In addition, the instruments that measure the solar atmosphere such as the CDS (Coronal Diagnostics Spectrometer) and UVCS (Ultraviolet Coronograph Spectrometer) observe both the inner and outer corona. They obtain measurements of temperature, density, composition, and velocity in the corona with high resolution. Finally, the instruments that analyze and measure the solar wind include ERNE (Energetic and Relativistic Nuclei and Electron experiment) and CELIAS (Charge, Element, and Isotope Analysis System) which measure the charge state and isotopic composition of ions in the solar wind.
