The sun is an interesting object in narrowband filters. For on-disk imaging you can study different
layers above the solar surface. The light from the sun is released from the photosphere, and it interacts with gas in the layers above by scattering or absorption. What you can see in a specific wavelength band is light that escapes from the "last surface of interaction" above the photosphere. For the H-alpha line core, the interaction is strong and the light escapes from high lying layers several hundred kilometers above the photosphere, and you see the chromosphere and prominences. Other wavelengths, such as the Calcium H and K lines and the Sodium D lines reveal other features. See the Solar Dynamics Observatory .
The Sun is a "magnetic star" with an activity level that varies with an 11 year period (see
sunspot number), with a full magnetic polarity cycle of 22 years. The magnetism is kept alive by the "solar dynamo", an enigmatic cyclic phenomenon generated by the electrically conducting, turbulent, and circulating solar plasma. The dynamo is the origin of the prominences, sunspots and other features seen in solar telescopes.
Other stars, and the Earth, have their own internal dynamos.
Use the menu above to see some results! I recommend using "Ctrl +/-" for zooming in and out. The top picture of coronal loops
is from the TRACE solar observatory.
