SOHO (Solar and Heliospheric Observatory) is a joint ESA (European Space Agency) and NASA mission to investigate the dynamics of the Sun. SOHO was the second spacecraft (after ISEE-3, 18 years earlier) to be placed in a halo orbit – in this case, an elliptical orbit around the first Lagrangian point (L1), 1.5 million kilometers ahead of Earth. In this orbit, it avoids solar eclipses by our planet. The data it collects will help astronomers understand how the solar corona is heated and how it expands into the solar wind, and will provide new insight on the Sun's structure and interior dynamics from the core to the photosphere. The spacecraft was built by ESA, tracking and data acquisition are shared by NASA and ESA, and mission operations are conducted by NASA.