G
o
o
g
l
e
All
News
Images
Videos
Maps
Shopping
Books
Search tools
Any time
Any time
Past hour
Past 24 hours
Past week
Past month
Past year
All results
All results
Verbatim
Coronal hole
View all
Coronal holes are regions of the Sun's corona that emit low levels of ultraviolet and X-ray radiation compared to their surroundings. They are composed of relatively cool and tenuous plasma permeated by magnetic fields that are open to...
Wikipedia