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The Solar and Heliospheric Observatory Project

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 SOHOs 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.

These two instruments also determine the charge and isotopic composition of energetic particles generated by the Sun. The sensitive instruments aboard the SOHO spacecraft have already helped scientists here on Earth discover and explain some of the mysteries of the Sun as well as to confirm some of their theories they previously held. For example, in May of 1998 with the help of the Michelson Doppler Interferometer scientists were able to see with greater clarity the giant convective cells inside and on the surface of the Sun.

With this information, scientists are now able to make out patterns of these convective cells on the Sun which in turn enhance their ability to predict future space weather as it affects the Earth. Another example of the SOHO spacecraft helping scientists to get a better understanding of the Suns properties is when scientists received a closer look at the solar wind via the SUMER instrument. For over 30 years now scientists have long thought that solar wind originated mainly from coronal holes on the surface of the Sun.

On February of 1999, however, scientists discovered that in actuality these outflows of solar wind are concentrated in specific patches at the edges of honeycomb shaped magnetic fields. These magnetic fields are associated with large convection cells just below the surface of the Sun. In addition, the spacecraft has a lot of routine tasks like taking daily images of the Suns corona via LASCOs ecliptic filter or capturing ions from the solar wind by way of the ERNE instrument.

The spacecraft has even helped to track and identify 102 new comets during the short course of its operation. In conclusion, the SOHO space project has given scientists around the world a better understanding of the brightest star in our sky. It has helped scientists unravel old mysteries and gave rise to new ones. Finally, this project will deepen our knowledge of the relationship between ourselves here on Earth and the most important giver of life in the solar system, our Sun.

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