Identifying the Unseen (August 7, 2009)
A few areas of this rather unremarkable solar image taken in extreme ultraviolet (UV) light on August 4, 2009, provide good starting points for explicating some of the unseen features of the Sun. For one thing, the darker polar coronal holes at the Sun's poles (top and bottom) are the source of open magnetic field lines (red) that head way out into space. They are also the source regions of the fast solar wind, which is characterized by a relatively steady speed of approximately 800 km/s. A more variable slow solar wind (gray) flows from all other areas of the Sun, carrying particles out into space. The solar wind defines the breadth of our solar system, the heliosphere. The image also shows a dark coronal hole at lower latitudes, just about facing towards Earth. The high speed solar wind particles (white) blowing from there will likely reach Earth in a few days and may spark some auroral activity. Lastly, magnetic loops (yellow) above the one sizeable active region arc out and connect back to an area of opposite polarity. Hot particles in these loops make them visible in UV light.
Safe to say, there is more than meets the eye when studying the Sun.
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.
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