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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27 Sep 2017
A Journey through the Solar Atmosphere with Ionized Magnesium
Credit: IRIS, LMSAL/NASA, Chad Madsen, SAO
Solar astronomers need to to come up with clever ways to represent the complexity of the solar atmosphere. The video here is an example of how we can visualize the dynamic solar atmosphere with the help of ionized Magnesium. Most of the other IRIS Movies of the Day represent 2D areas of the Sun that advance forward in time as the movie plays. This movie, however, is a bit more complicated. The vertical axis represents space like in the other movies; specifically, it shows light entering IRIS's narrow spectrograph slit. However, the horizontal axis represents time in this case, so moving farther right shows the light entering the slit at a later time. Furthermore, as the movie plays, it's actually stepping forward in wavelength instead of time. So, why is useful to show the Sun this way? For one, by stepping through wavelength instead of time, we can actually get a picture of what's going on at different altitudes of the solar atmosphere. In this case, we're taking a look at emission produced by ionized Magnesium at different wavelengths. Ionized magnesium tends to emit light over a short range of wavelengths; most of the light is emitted at a central wavelength, known as 'core emission', with a smaller amount of light emitted at surrounding wavelengths, known as 'wing emission'. The wing emission tends to originate from deep down in the solar atmosphere while the core emission tends to originate from much higher up. This movie starts at the shorter wavelength wing of ionized Magnesium, steps its way towards the core, and then to the longer wavelength wing. The central dark stripe you see is actually a sunspot. We first see it in the low altitude wing emission which shows a dark sunspot that isn't changing to much in time as you move to the right. Suddenly, when we advance into the high altitude core emission, we see a stunning pattern of bright chevrons produced by sunspot waves in the upper atmosphere. Surrounding the sunspot, we also see a complex web of cool, dark material superimposed on hot, bright material, exemplifying the complexity of the upper atmosphere. We then move into the long wavelength wing emission which shows the docile lower atmosphere once again. The movie is sort of like standing in the lower atmosphere, jumping up quickly to take a brief look at the upper atmosphere, and then falling back down to the lower atmosphere.