Quiet? Not Quite!
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Caption: Although the last couple of weeks have been very uneventful in terms of large flares and coronal mass ejections, the Sun is by no means a quiet and unchanging object. For two and a half hours on 11 July, EIT made a special set of observations that do not use the shutter between exposures, but instead relies on the fact that the detector readout time is much shorter than the exposure time. The same region was also observed by the TRACE spacecraft, at a different wavelength (171 Å).
A number of smaller events can be seen throughout the EIT movie, and it serves as a reminder that even though some large features appear to change little from one 304 Å image to the next (usually 6 hours), there are many things that are happening on a much shorter timescale. The time between subsequent images is approximately 1min 8sec, with some gaps.
During shutterless operations like this, an operator must be on alert the whole time to avoid accidental overexposure in case of a large flare, since this could cause a burn-in on the detector. Also, the observations are strongly limited by the telemetry - therefore only part of the field of view is selected for processing. Nevertheless, the buffer fills up slowly, and some gaps are inserted to allow "draining", and the total length of the observation sequence has to be limited.
Extreme ultraviolet Imaging Telescope (EIT); Transition Region And Coronal
Taken: 11 July 2001, 16:01-18:26 UT
Picture credits:SOHO/EIT (ESA & NASA), TRACE