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.
A tomographic view of the birth of an active region
Credit: IRIS, LMSAL/NASA, Bart De Pontieu
IRIS is operated through so-called timelines that are uploaded five times per week. An IRIS science planner essentially chooses the most interesting targets and observing programs for the next one to three days (weekends) and includes these in the timeline. Since the IRIS field-of-view only covers about 1% of the solar disk, the planner has to make tricky decisions on where to point in order to capture the most scientifically interesting event. Much of the time, IRIS is pointed at active regions that have already emerged from below the surface, but it is rare to catch an active region being born since there is usually very little lead time and most of the IRIS observations are planned 24 hours in advance. The movie shows a rare example of IRIS capturing the birth of an active region under the slit. This is a collection of a variety of different observing programs that accidentally captured the active region while studying a filament. Because the IRIS spectral rasters cover so many different spectral lines that are formed at different heights in the low solar atmosphere, IRIS allows for an unprecedented tomographic view of this active region as it emerges from below the surface. The movie shows rasters in 6 different special lines that are formed (in increasing height) at the surface of the Sun (photosphere), just above the surface (upper photosphere), in the low chromosphere (Mg II triplet line), the middle chromosphere (Mg II k2v and Mg II k2r) and the top of the chromosphere (Mg II k3). These measurements over the course of many days show how a tiny region of activity leads to increased heating and brightness in all layers of the atmosphere as the magnetic fields of the new active region start interacting with pre-existing fields and drags up plasma from the surface to greater heights. This type of data provides unique constraints for increasingly more sophisticated numerical models of the emergence of new magnetic flux to form an active region, an area of very active research.