Sun in H-alpha
This image was taken with a H-alpha telescope, which is specially designed for sun observations. The telescope is equipped with an interference filter that transmits light only in a narrow spectral range that corresponds exactly to the wavelength of excited hydrogen at 656.281 nm. It is called H-alpha because it is the brightest hydrogen line in sunlight. To show both protuberances and the surface of the sun it is necessary to adjust the telescope and take two seperate images, which are then combined in post.