Happy 23rd Birthday! (December 3, 2018)
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The 2nd of December 2018 marks the 23rd launch anniversary of the Solar and Heliospheric Observatory (SOHO). SOHO is the longest-lived heliophysics mission still operating and has provided a nearly continuous record of solar and heliospheric phenomena over a full 22-year magnetic cycle (two 11-year sunspot cycles). SOHO's findings have been documented in over 5,000 papers in the peer reviewed literature, authored by more than 4,000 scientists worldwide.
SOHO provided the first ever images of structures and flows below the Sun's surface and of activity on the far side of the Sun. SOHO discovered sunquakes and eliminated uncertainties in the internal structure of the Sun as a possible explanation for the "neutrino problem" which concerned the large discrepancy between the high flux of solar neutrinos -- particles which are now believed to possess mass and travel at almost the speed of light -- predicted from the Sun's luminosity and the much lower flux that is observed.
The ultraviolet imagers and spectrometers on SOHO have revealed an extremely dynamic solar atmosphere where plasma flows play an important role and discovered dynamic solar phenomena such as coronal waves. SOHO measured the acceleration profiles of both the slow and fast solar wind and identified the source regions of the fast solar wind.
SOHO revolutionized our understanding of solar-terrestrial relations and dramatically boosted space weather forecasting capabilities by providing, in a near-continuous stream, a comprehensive suite of images covering the dynamic atmosphere and extended corona. SOHO has measured and characterized over 28,000 coronal mass ejections (CMEs). CMEs are the most energetic eruptions on the Sun and the major driver of space weather. They are responsible for all of the largest solar energetic particle events in the heliosphere and are the primary cause of major geomagnetic storms. SOHO's visible-light CME measurements are considered a critical part of the US National Space Weather Action Plan.
For two solar activity cycles SOHO has measured the total solar irradiance (the "solar constant") as well as variations in the extreme ultraviolet flux, both of which are important to understand the impact of solar variability on Earth's climate. Besides watching the Sun, SOHO has become the most prolific discoverer of comets in astronomical history: as of late 2018, more than 3,400 comets have been found by SOHO, most of them by amateurs accessing SOHO real-time data via the Internet.
SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.
If your institution would also like to receive the same Weekly Pick from us for display (usually in Photoshop or QuickTime format), please send your inquiry to steele.hill@gsfc.nasa.gov.
