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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3 Aug 2017
IRIS and the solar eclipse on 21-Aug-2017
Credit: IRIS, LMSAL/NASA, Bart De Pontieu
IRIS is in a low-Earth orbit. The orbital altitude is low enough (about 600 km) that the Sun can, in principle, be eclipsed by the Earth every orbit. However, the IRIS orbit was chosen to be sun-synchronous so that IRIS sees the Sun continuously between mid February and end of October. The Sun does get eclipsed many times per year for IRIS, both by the Earth and by the Moon. During the winter in the northern hemisphere, IRIS sees eclipses of the Sun by the Earth every orbit (97 minutes). Typically twice per year, IRIS observes eclipses of the Sun by the Moon ("solar eclipses"), the same type of eclipse that will be visible from North America on 21-Aug-2017. The movie shows a previous example of the Moon moving across an active region on the Sun, in April 2014. Measurements such as these look pretty but can also be used to help calibrate our instrument. The bright dots visible after the Moon has occulted the whole field-of-view are an artefact of our "dust buster" -- software that removes tiny blemishes on the detector.