Coronal holes are regions where the sun's corona is dark. These features were discovered when X-ray telescopes were first flown above the Earth's atmosphere to reveal the structure of the corona across the solar disc. Coronal holes are associated with 'open' magnetic field lines and are often found at the sun’s poles. The high-speed solar wind is known to originate in coronal holes. The solar wind escaping from this hole will reach Earth around June 5-7, 2012.