Large coronal hole A large coronal hole is easy to spot in this image of the Sun from SDO's AIA instrument. In the extreme UV wavelength of 193 Angstroms, the dark coronal hole extends from the top of the Sun to almost halfway down (May 27, 2010). Coronal holes are magnetically open areas from which high-speed solar wind streams out into space. They appear darker in this wavelength because there is just less of the material that is being imaged, in this case ionized iron. This is one of the most substantial coronal hole areas spotted on the Sun in many months.