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# Long description

Figure 13a shows a hydrogen-alpha image of the Sun. Many more features can be seen compared to a white-light image of the solar disc. These include a number of bright spots, and dark lanes which cross the Sun. These bright lanes are revealed on the edges of the solar disc as prominences: bright regions that stick up above the surface of the Sun in pillars, arcs or arches.

Figure 13b shows an optical image of the galaxy M82. Seen as an edge-on disc, the galaxy takes on a very flattened, cigar-like shape as seen from Earth. Superimposed is an image of hydrogen gas. Highly clumped, fan-like structures of hydrogen can be seen emanating from the galaxy, perpendicular to the disc, in regions where there is no emission in the optical image.