Solar Heliospheric Observatory

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Solar Heliospheric Observatory

(SOHO) An ESA satellite, with some NASA instrumentation, launched in 1995 into a halo orbit around the L1 Lagrangian point – the point 1.5 million km from Earth at which the gravitational pull of Sun and Earth balance. SOHO is designed to study the Sun's internal structure (see helioseismology), and the physical processes that form and heat the solar corona and give rise to the solar wind, which permeates the heliosphere. SOHO is part of ESA's contribution to the Solar/Terrestrial Energy Programme (STEP). Although its primary mission is to study the Sun, many of SOHO's solar images made using coronagraphs to block out the photosphere have revealed numerous hitherto unknown comets. By the start of 2005, SOHO had ‘discovered’ well over 900 comets.