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 Prominence and a Filament: Two Faces of the Same Person
Credit: IRIS, LMSAL/NASA, Wei Liu
Solar prominences are cool material suspended in the million-degree hot corona. In general, they appear as bright emission against the dark background when viewed off the solar limb, and as dark absorption against the emission from the atmosphere underneath it when viewed on the bright solar disk - so termed filaments. In a sense, a prominence and a filament are two faces of the same person, depending on the viewing perspective of the observer with respect to its position on the Sun. This movie, taken on 2020-Sep-15 by IRIS, offers a not-so-common opportunity to capture the two faces of a single prominence at the same time, both under the IRIS slit. Part of it is located on the solar disk appearing as a filament and the rest extends above the limb appearing as a prominence. The movie shows a raster sequence in time at four wavelength positions of the Mg II 2796 Angstrom line (as shown at the top), offering a glimpse at four separate optical depths of the solar atmosphere, like a tomography. The prominence and filament are evident near the core of this spectral line (two middle panels), while it is absent in the blue and red wings, meaning they appear "transparent" (two outer panels). We can clearly see some thread-like structures and mass motions in the prominence and filament. With further analysis, such IRIS data can offer unique clues about the nature and dynamics of solar prominences and filaments in general.