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The Gateway to Astronaut Photography of Earth
(NASA Crew Earth Observations)
Astronaut Photography of Earth - Display Record
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IdentificationMission: ISS020 Roll: E Frame: 26195 Mission ID on the Film or image: ISS020
Country or Geographic Name: CHAD
Features: AOROUNGA IMPACT CRATER, YARDANGS
Center Point: Latitude: 19.1 Longitude: 19.2 (Negative numbers indicate south for latitude and west for longitude)
Stereo: (Yes indicates there is an adjacent picture of the same area)
ONC Map ID: JNC Map ID:
CameraCamera Tilt: 42
Camera Focal Length: 800mm
Camera: N3: Nikon D3
Film: 4256E : 4256 x 2832 pixel CMOS sensor, 36.0mm x 23.9mm, total pixels: 12.87 million, Nikon FX format.
Percentage of Cloud Cover: 10 (0-10)
GMT Date: 20090725 (YYYYMMDD) GMT Time: 105733 (HHMMSS)
Nadir Point Latitude: 21.5, Longitude: 20.7 (Negative numbers indicate south for latitude and west for longitude)
Nadir to Photo Center Direction: Southwest
Sun Azimuth: 242 (Clockwise angle in degrees from north to the sun measured at the nadir point)
Spacecraft Altitude: 187 nautical miles (346 km)
Sun Elevation Angle: 86 (Angle in degrees between the horizon and the sun, measured at the nadir point)
Orbit Number: 1198
CaptionsAorounga Impact Crater, Chad
Aorounga Impact Crater is located in the Sahara Desert, in north-central Chad, and is one of the best preserved impact structures in the world. The crater is thought to be middle or upper Devonian to lower Mississippian (approximately 345–370 million years old) based on the age of the sedimentary rocks deformed by the impact. Spaceborne Imaging Radar (SIR) data collected in 1994 suggests that Aorounga is one of a set of three craters formed by the same impact event. The other two suggested impact structures are buried by sand deposits.
The concentric ring structure of the Aorounga crater—renamed Aorounga South in the multiple-crater interpretation of SIR data—is clearly visible in this detailed astronaut photograph. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.
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Recommended Citation: Earth Science and Remote Sensing Unit, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth." .