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Lights On and Over the Southern Horizon

Lights On and Over the Southern Horizon

While passing over the Great Australian Bight and the cloud-covered Indian Ocean, NASA astronaut Jack Fischer looked south from the International Space Station and photographed the glowing green lights of the aurora australis. The blue glow of dawn appears at the far left, the ISS solar arrays jut into the foreground, and stars fill the space above the edge of the atmosphere.

The aurora australis (southern lights) occurs when charged particles from the magnetosphere (the magnetic space around Earth) are accelerated by the solar wind or storms from the Sun. The pressure and magnetic energy of solar plasma stretches and twists the magnetic field, particularly on the night side of Earth. This energizes particles trapped in our magnetic field, and that energy is released suddenly as the field lines snap the particles down field lines toward the north and south magnetic poles.

These fast-moving electrons collide with Earth’s upper atmosphere, transferring their energy to oxygen and nitrogen molecules and making them chemically “excited.” As the gases return to their normal state, they emit photons—small bursts of energy in the form of light. The color of light reflects the type of molecules releasing it; oxygen molecules and atoms tend to glow green, white, or red, while nitrogen tends to be blue or purple. This ghostly light originates at altitudes of 100 to 400 kilometers (60 to 250 miles).

The fainter arc of light that parallels the horizon—airglow—is another manifestation of the interaction of the Earth’s atmosphere with radiation from the Sun.

Jack Fischer took more than 2000 photos of the aurora and atmopshere in this sitting on June 19, 2017, which you can see here. Similar time-lapse sequences have been turned into videos of the dancing auroral lights.

Astronaut photograph ISS052-E-4998 was acquired on June 19, 2017, with a Nikon D4 digital camera using a 24 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 52 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Story by Mike Carlowicz.

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