For the past two weeks, sunspot AR12371 has been crackling with flares, radio bursts, and solar storms as it has moved across the Earth-facing side of the Sun. Overnight on June 20-21, that active region launched a CME toward Earth that caused a severe geomagnetic storm on June 22-23. Skywatchers as far south as Texas reported aurora borealis on the horizon. Another flare burst from the region early on June 23 and may be connected with the activity shown at the top of this page. Still another Earth-directed CME exploded from the Sun on June 25, and space weather forecasters were anticipating more atmospheric light shows on June 27.
Auroras occur when solar flares and coronal mass ejections—or even strong solar wind streams—disturb and distort the magnetosphere, the space protected by Earth’s magnetic field. The collision of pressure waves and solar particles into the magnetosphere accelerates particles trapped in the space around Earth (such as in the radiation belts). Those particles flow down into Earth’s upper atmosphere (about 100 to 400 kilometers in altitude) where they excite oxygen and nitrogen molecules and release photons of light. The results are rays, sheets, and curtains of light in the sky centered around both of Earth’s magnetic poles.