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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10 Jul 2018
Flare Shines Light on Dark Structures
Credit: IRIS, LMSAL/NASA, SAO, Jakub Prchlik
IRIS observes a small B1.1 flare during a coordinated observation with the Swedish Solar Telescope. The flare is easily visible in the top right as a brightening in the 1330 Angstrom context image at 08:02 UT. In the middle of the raster image is a thin line, which allows light through to the spectrograph. The slit passes over the flare region, so we are able to gather detailed information about the flare from its spectrum. The Mg II k line at 2796 Angstroms clearly shows dark structures in the line core due to absorption along the line of sight, which is likely coronal rain. After the flare, we see the dark structure in the Mg II k line move to the right, which indicates motion towards the solar surface. We see the dynamics of the absorbing material starts at the same time as the flare when we focus on the Mg II k line (the second movie). In the movie, the left and right panels are the continuum blue and red of the Mg II k line, while the center left and center right panels are just blue and red of the Mg II k line core. We see in both center panels the absorption darkens and moves upwards after the flare. The dark absorption does not last throughout the observation. First, the blue shifted absorption fades, then the red. After which, all panels look similar to what they looked like at the start of the observation. The evolution of these dark, absorbing regions remains an area of active research, but IRIS observations help shine light on the dark, cool plasma.