SOHO - listening to the Sun's song
The Solar and Heliospheric Observatory (SOHO) is a project of
international cooperation between ESA and NASA to study the Sun, from
its deep core to the outer corona, the solar wind, and its interaction
with the interstellar medium. A consortium of European space companies
built SOHO under overall management by ESA, and twelve international
consortia developed its suite of instruments. SOHO is operated from
NASA Goddard Space Flight Center in Greenbelt, Maryland. SOHO moves
around the Sun in step with the Earth, by slowly orbiting around the
First Lagrangian Point (L1), where the combined gravity of the Earth
and Sun keep SOHO in an orbit locked to the Earth-Sun line. The L1
point is approximately 1.5 million kilometres away from Earth (about
four times the distance of the Moon), in the direction of the Sun.
There, SOHO enjoys an uninterrupted view of our daylight star.
Visible light, UV and EUV telescopes measure magnetic fields, temperatures, densities, flows and dynamic phenomena such as flares and coronal mass ejections in the Sun's atmosphere. Other instruments record the energy distribution and chemical composition of the solar wind and energetic particles. Three instruments listen to the "Song of the Sun". The entire Sun vibrates from a complex pattern of acoustical waves, much like a bell. By tracking and deciphering these sound waves - a technique called "helioseismology" - scientists can learn about the complex interior of our daylight star.
Detail from SOHO/EIT 195 image (Extreme-ultraviolet Imaging Telescope with 195
latest EIT171 (blue), EIT184 (yellow), EIT304 (red) and MDI
SOHO official project site
Background: The sun - a 1 million km wide ball of burning gas
Helioseimology: Sounds of the Sun
Global Oscillation Network Group