The video was captured using deep ultraviolet range filters, so that the large coronal hole would be visible on the solar disk. Beneath the coronal hole there is a darker area in the heliosphere with an increased solar wind speed. Reduced brightness of coronal holes is associated with the mass escape of plasma from these regions into interplanetary space.
Our Sun-watching satellite saw a coronal hole on the Sun on May 2-4 👀 Coronal holes — a perfectly normal occurrence — appear as dark areas when seen in certain wavelengths of extreme ultraviolet light, like in these images. https://t.co/HYZePndwpB pic.twitter.com/QtKFwfld0Z
— NASA Sun & Space (@NASASun) 10 мая 2018 г.
