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Stormy Sun

A coronal mass ejection

A huge explosion from the surface of the Sun, known as a coronal mass ejection. (The direct light from the Sun has been blocked out by the black disc; the white circle shows the size of the Sun.)

  • Coronal mass ejection, a huge solar explosion
  • Can expel a billion tonnes of matter
  • Moves at 1.5 million kilometres per hour

Solar storms bombard Earth with a stream of electrons and other charged particles that interact with gases in our atmosphere to generate colourful aurora.

A coronal mass ejection, a large solar storm, can expel a billion tonnes of matter at a 1.5 million kilometres per hour or more.

The strongest solar storms have the potential to interfere with communications, power grids, and satellites. Solar storms happen most frequently when the Sun is in the active phase of its 11-year cycle, called solar maximum.

Though the Sun was expected to be entering solar maximum in 2010, it had been unusually quiet for at least two years. Despite its relative lack of activity, the Sun released a series of four coronal mass ejections between May 22 and May 24, 2010.

The images above and below show one coronal mass ejection on May 23.

Both images were taken by the Solar Terrestrial Relations Observations (STEREO) Ahead spacecraft. The top image is from 20:09:15 Universal Time (UT). STEREO Ahead acquired the other image just over two hours later at 22:24:00 UT.

A coronal mass ejection

In this image taken two hours after the first one, the coronal mass ejection can be seen streaming away from the Sun.

In the top image, a bright mass of charged particles loops from the Sun’s atmosphere. In the second image, the looped mass had expanded and was moving away from the Sun.

See the full-size images here and here (will open in new windows).

The images show only the Sun’s corona, the outermost layer of the atmosphere. A dark disc covers the rest of the Sun, and a white circle represents the Sun’s surface.

When the charged particles from May’s coronal mass ejections reached Earth, they caused no damage, but they did generate sheets of coloured light dancing across polar skies.

NASA images courtesy the Solar Terrestrial Relations Observatory Team. Text adapted from information issued by Holli Riebeek.

The Sun’s stormy surface

An image captured by NASA's SOHO spacecraft shows storms brewing on the Sun.

A flare and a storm brewing on the surface of the Sun.

Magnetic storms from the Sun bombard Earth with charged particles that can interfere with electronics systems and satellites. This image, captured by NASA’s Solar Terrestrial Relations Observatory (STEREO) Ahead spacecraft on February 12, 2010, shows one such storm (albeit a very small one) brewing on the solar surface.

Two active regions glow brightly in this ultraviolet image of the Sun. A small flare rises from the active area on the left. Flares are intense explosions on the Sun that blast radiation into space. This one paints a white line across the left horizon of the Sun.

The active area on the right churns with magnetic loops. Arcs of charged particles rise from the surface and are drawn back down again in the magnetic field. A video showing a sequence of STEREO observations, including this one, reveals that a small coronal mass ejection (CME) burst from this region a short time after this image was taken. Like a flare, a CME sends charged particles and energy into space, but CMEs are larger solar storms that both last longer and carry a larger cloud of particles and magnetic field into space than do flares.

Artist's impression of the twin STEREO Sun-monitoring spacecraft.

Artist's impression of the twin STEREO Sun-monitoring spacecraft.

Both flares and coronal mass ejections can create space weather if aimed at Earth. The charged particles from large storms blast Earth’s magnetic field, which acts as a shield. The charged particles interacting with Earth’s magnetic field generate intense and beautiful aurora, but they can also be destructive. Solar storms in the past have damaged power grids, causing blackouts, and harmed and destroyed satellites.

STEREO is one of several NASA missions studying the Sun. STEREO was launched to help scientists better understand coronal mass ejections. An improved understanding of solar storms will improve space weather forecasts, which will help limit the damage they cause on Earth.

NASA image courtesy the STEREO science team. Text adapted from information issued by the STEREO science team and Holli Riebeek.