Launch of Solar and Heliospheric Observatory

The Solar and Heliospheric Observatory, SOHO, is a joint project of the European Space Agency and NASA to study the Sun, from its deep interior to its outer corona and the solar wind. It was launched on an Atlas rocket and placed near the first Lagrange point, about 1.5 million kilometers from Earth toward the Sun, where it has a constant view of the star. SOHO has transformed solar physics, with discoveries about the Sun's interior through helioseismology, and with continuous images of coronal mass ejections that help forecast space weather. Its coronagraphs have also made it the most prolific comet finder in history, as thousands of small comets that graze the Sun were discovered in its images. It has operated for far longer than planned.

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