Developing coronal holes Two coronal holes that develop over several days stand out in this image and video clips of the Sun from SDO's AIA instrument (Jan. 9-12, 2010). In the movie one dark coronal hole intensifies just above the Sun's equator and a second one appears lower down and to the left near the end of the clip. Coronal holes are magnetically open areas from which high-speed solar wind streams out into space. They appear darker in this wavelength (the extreme UV wavelength of 193 Angstroms) because there is just less of the material that is being imaged, in this case ionized iron. When rotation carries a coronal holes past the Sun center, the solar wind stream begins to be aimed towards Earth where it can begin to generate aurorae on Earth, especially in the higher latitudes.