The Solar and Heliospheric Observatory (SOHO)

The Solar and Heliospheric Observatory (SOHO) is a spacecraft that is currently investigating the entire Sun, from the core to the outer corona and the solar wind.The spacecraft is build by a European industrial consortium led by Matra Marconi Space (now Astrium) that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered 1900 comets. It began normal operations in May 1996. It is a joint project of international cooperation between the European Space Agency (ESA) and NASA. Originally planned as a two-year mission, SOHO currently continues to operate after over ten years in space. In October 2009, a mission extension lasting until December 2012 was approved. 

The 610 kg SOHO spacecraft is in a halo orbit around the Sun-Earth L1 point, the point between the Earth and the Sun where the balance of the (larger) Sun's gravity and the (smaller) Earth's gravity is equal to the centripetal force needed for an object to have the same orbital period in its orbit around the Sun as the Earth, with the result that the object will stay in that relative position. 

         Halo Orbit                                    L1 Point