Solar and Heliospheric Observatory

The Solar and Heliospheric Observatory (SOHO) is a joint NASA–ESA spacecraft launched in 1995 to study the Sun and solar wind from a halo orbit near the Sun–Earth L1 point.

Sun–Earth L1: The first Sun–Earth Lagrange point, where gravitational and orbital effects allow spacecraft to remain near Earth’s direction from the Sun. SOHO’s halo orbit near L1 keeps Earth between the spacecraft and the Sun, enabling continuous solar observations.
Coronal mass ejection: A large eruption of magnetized plasma from the Sun’s corona into interplanetary space. SOHO’s coronagraphs reveal these eruptions and help estimate their direction and speed.
NASA: The United States government agency responsible for civilian space exploration and aeronautics. NASA developed and operated SOHO in partnership with ESA.
Bernard Fleck: A solar physicist who served as SOHO project scientist and helped lead its scientific program. Fleck coordinated SOHO’s scientific work and public communication.
Halo orbit: A three-dimensional periodic orbit around a Lagrange point in a rotating two-body system. SOHO circles L1 in a halo orbit rather than sitting motionless at the point.
Space weather: Conditions in space near Earth, shaped chiefly by solar activity and its effects on the magnetosphere and atmosphere. SOHO’s near-real-time solar observations help identify disturbances that may affect Earth.
European Space Agency: An intergovernmental organization that coordinates space activities among its member states. ESA supplied spacecraft systems and instruments and shared responsibility for the mission.
Eugene Parker: An American astrophysicist whose theory of the solar wind transformed solar and space physics. SOHO’s investigations of the solar wind addressed questions Parker’s theory had made central.
Coronagraph: An instrument that blocks direct light from a bright source to reveal faint surrounding structures. SOHO’s coronagraphs occult the solar disk to image the much fainter corona.
Solar flare: A sudden, intense release of energy and radiation from the Sun’s atmosphere. SOHO records flares and the changing ultraviolet and extreme-ultraviolet emission they produce.

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