IRIS Movie of the Day
At least once a week a movie of the Sun taken by NASA's Interface Region Imaging Spectrograph (IRIS) is posted by one of the scientists operating the instrument.
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22 Aug 2017
IRIS eclipse movie #2
Credit: IRIS, LMSAL/NASA, Bart De Pontieu
This movie shows the second eclipse that IRIS saw on 21-Aug-2017. We again see light from a spectral line called Mg II k that is sensitive to gases from the chromosphere, a layer that is sandwiched between the Sun's surface and the Sun's corona (visible during total solar eclipses). This movie shows the effects that the solar eclipse has on the instrument stabilization system of IRIS, which is based on a guide telescope that looks at the full disk. Under normal conditions, IRIS uses this guide telescope image of the Sun to stabilize the instrument down to a small fraction of an arcsecond (allowing us to see features as small as a few hundred km on the Sun, which is 150 million km from Earth). However, when the moon starts to cover the full disk of the Sun, the instrument stabilization loses track and IRIS drops out of "fine sun point" mode. The orientation of IRIS is still quite stable, but the movie shows more jitter. The bright dots that remain when the Moon obscures the Sun are an artifact of image processing to remove small blemishes on the detector. Watch the movie all the way to the end to see the Sun make its re-appearance after the eclipse ends. This second eclipse was almost, but not quite, a total eclipse from the IRIS vantage point.