The Solar & Heliospheric Observatory (SOHO) project is the cooperative effort between NASA and the ESA (European Space Agency) that was designed to study the internal structure and outer atmosphere of the Sun, as well as the origin of the solar wind.
First launched on December 2, 1995, the SOHO has provided scientists with an abundance of information about the Sun. It has also made other notable achievements such as revealing the first images of the convection zone of a star; giving precise measurements of the temperature structure, interior rotation, and gas flows in the solar interior; and enhancing the ability to forecast space weather by giving up to three days notice of earth directed disturbances. Unlike other satellites SOHO orbits the Sun instead of the Earth, and is situated so that it can observe the Sun at all times and send its data back to Earth. As of 2008, scientists began testing new method using data collected from SOHO to predict in real time the intensity of approaching hazardous solar particles that pose a threat to astronauts and technology in space. It was also during this time that SOHO observed a special solar spot on the Sun that alerted scientists to the fact that anew solar cycle had begun.
To date SOHO has become the most successful discoverer of comets in history. During its mission SOHO has discovered more than 1350 comets; many of the comets discovered are periodic meaning that they orbit around the Sun more than twice during their orbital periods. The SOHO has also been able to help scientists predict when sunspot flare-ups will occur, and how strong they will be. This information helps NASA determine whether or not to do spacewalks or other activities outside the space shuttle without causing harm to the astronauts.
SOHO has been so successful that its mission has been extended several times, with the latest extension expected to last until the end of 2012.