STS-099 Earth Sciences and Image Analysis Photographic Highlights

TOP PICKS

Click here to view the complete online collection of astronaut photography of Earth >>

STS099-355-24

STS099-355-24         Click the photo number to access all resolutions available and the database record.

Airglow and Difuse Red Aurora Borealis: There are two separate atmospheric optical phenomena in the photo. The thin greenish band above the horizon is airglow; radiation emitted by the atmosphere from a layer about 30 km thick and about 100 km altitude. The predominant emission in airglow is the green 5577 Angstrom wavelength emission from atomic oxygen atoms, which is also the predominant emission from the aurora. A yellow-orange color is also seen in airglow, which is the emission of the 5800 Angstrom wavelength from sodium atoms. Airglow is always and everywhere present in the atmosphere; it results from the recombination of molecules that have been broken apart by solar radiation during the day. But airglow is so faint that it can only be seen at night by looking "edge on" at the emission layer, such as the view astronauts have in orbit. The other phenomenon in the photo appears to be a faint, diffuse red aurora. Red aurora occur from about 200 km to as high as 500 km altitude only in the auroral zones at polar latitudes. They are caused by the emission of 6300 Angstrom wavelength light from oxygen atoms that have been raised to a higher energy level (excited) by collisions with energetic electrons pouring down from the Earth's magnetosphere. The light is emitted when the atoms return to their original unexcited state. With the red light so faint in this picture, that means that the flux density of incoming electrons was small. Also, since there is no green aurora below the red, that indicates that the energy of the incoming electrons was low - higher energy electrons would penetrate deeper into the atmosphere where the green aurora is energized. In this particular photo, the star streaks in the background are longer than in the other photos in the set. This shows that the crew used a longer exposure in this photo to bring out the faint red. Astronaut Tom Jones gives a nice astronaut perspective of airglow on the web at http://neurolab.jsc.nasa.gov/jones.htm.

< Back

This server is scheduled to be off starting the evening of Thursday October 10 and ending the morning of Tuesday October 15 to accommodate a scheduled power outage.

This service is provided by the International Space Station program and the JSC Astromaterials Research & Exploration Science Directorate. Recommended Citation: Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth." .
	NASA Responsible Official: Tracy Calhoun Curator: jsc-earthweb@mail.nasa.gov Contributors: Earth Sciences Web Team	National Aeronautics and Space Administration Lyndon B. Johnson Space Center	International Space Station National Laboratory Last Update:
Server: 1