SOHO, the Solar and Heliospheric Observatory, is the spacecraft launched in 1995 to observe the Sun from the vicinity of the Sun–Earth L1 point. It is a joint mission of the European Space Agency and NASA, launched on 2 December 1995.
L1 lies about 1.5 million kilometres from Earth toward the Sun, where the gravitational effects of Earth and the Sun allow a spacecraft to remain aligned with Earth's orbit around the Sun. SOHO actually follows a halo orbit around L1 rather than sitting precisely at the mathematical point. This position gives it an almost uninterrupted view of the Sun and allows it to monitor solar wind before it reaches Earth.
Its instruments study the solar atmosphere, solar wind, magnetic activity, and the Sun's interior through helioseismology. SOHO has become especially valuable for space-weather forecasting and has also discovered thousands of comets.
Solar Orbiter and Parker Solar Probe are newer solar missions, while STEREO used two spacecraft in different solar orbits. None is the 1995 L1 observatory described here.