XRT Picture of the Week (XPOW)

In the XRT image, seen in the movie, the northern ring has a darker than normal center and the smaller, southern ring has a bright X-ray center. These loop structures are nowhere near an active region so what's going on up there?

To find out why these rings exist, we must look at H-alpha data. H-alpha is a particular wavelength of light, 656.28 nm, that is useful for seeing solar filaments and prominences. When we overlay the XRT image onto a NSO/Gong H-alpha image, we see that both coronal cavities sit directly above two separate prominences.

The upper cavity has a dark center because the prominence sits high up into the corona and is actually blocking some of the X-rays -- a dark chewy nougat. This actually appears bright in the composite image because the prominence is bright in H-alpha.

However, the prominence in the lower ring does not extend high up into the cavity and doesn't block any X-rays. In fact, a bright X-ray core, has developed above it. -- a traditional chewy nougat.

Whether the cavity has a chewy nougat core or not, coronal cavities are complex magnetic structures that are a source of space weather. Interested readers can visit here for more information.

Keywords: Cavity, Limb
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