ISS018-E-14770
| NASA Photo ID | ISS018-E-14770 |
| Focal Length | 400mm |
| Date taken | 2008.12.20 |
| Time taken | 13:14:41 GMT |
Resolutions offered for this image:
1000 x 2551 pixels 666 x 999 pixels 720 x 1080 pixels 540 x 1378 pixels 3072 x 2098 pixels 640 x 437 pixels
1000 x 2551 pixels 666 x 999 pixels 720 x 1080 pixels 540 x 1378 pixels 3072 x 2098 pixels 640 x 437 pixels
Cloud masks available for this image:
Spacecraft nadir point: 23.7° N, 12.9° E
Photo center point: 24.5° N, 12.1° E
Photo center point by machine learning:
Photo center point: 24.5° N, 12.1° E
Photo center point by machine learning:
Nadir to Photo Center: Northwest
Spacecraft Altitude: 188 nautical miles (348km)
Country or Geographic Name: | LIBYA |
Features: | MURZUQ LINEAR AND STAR DUNES |
| Features Found Using Machine Learning: | |
Cloud Cover Percentage: | 10 (1-10)% |
Sun Elevation Angle: | 34° |
Sun Azimuth: | 216° |
Camera: | Nikon D2Xs Electronic Still Camera |
Focal Length: | 400mm |
Camera Tilt: | 20 degrees |
Format: | 4288E: 4288 x 2848 pixel CMOS sensor, RGBG imager color filter |
Film Exposure: | |
| Additional Information | |
| Width | Height | Annotated | Cropped | Purpose | Links |
|---|---|---|---|---|---|
| 1000 pixels | 2551 pixels | No | Yes | Earth From Space collection | Download Image |
| 666 pixels | 999 pixels | Yes | Yes | Earth From Space collection | Download Image |
| 720 pixels | 1080 pixels | Yes | Yes | Download Image | |
| 540 pixels | 1378 pixels | Yes | Yes | Download Image | |
| 3072 pixels | 2098 pixels | No | No | Download Image | |
| 640 pixels | 437 pixels | No | No | Download Image |
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Image Caption: Sand Dunes, Marzuq Sand Sea, Southwest Libya
This detailed astronaut photograph, taken from low earth orbit, shows classic large and small sand masses of the central Sahara Desert, where wind is a more powerful land-shaping agent than water. "Draa" dunes (from the Arabic for "arm") are very large masses of sand, and they appear here as the broad network of yellow-orange sand masses, with smooth-floored, almost sand-free basins between them. These sand masses lie in the western part of Libya's vast Marzuq Sand Sea (centered at 24.5 degrees north, 12 degrees east). Geologists think that the draa of the Marzuq were probably formed by winds different from the prevailing north-northeast winds of today.
Numerous smaller dunes have developed on the backs of the draa. Three distinct dune types are visible: longitudinal dunes, which are more or less parallel with the north winds; transverse dunes, which are usually more curved and formed at right angles to the wind; and star dunes, in which several linear arms converge towards a single peak.
The upwind sides of the sand masses appear smoother than the downwind side. Wind is moving sand grains almost all the time. This means that the draa and the dunes are all moving as sand is added on the upwind side and blown off the downwind side. Small sand masses move much faster than large sand masses. The draa are almost stationary, but the smaller dunes move relatively quickly across their backs. When the smaller dunes reach the downwind side of the draa, they are obliterated; their sand is blown across the basins as individual grains.
This detailed astronaut photograph, taken from low earth orbit, shows classic large and small sand masses of the central Sahara Desert, where wind is a more powerful land-shaping agent than water. "Draa" dunes (from the Arabic for "arm") are very large masses of sand, and they appear here as the broad network of yellow-orange sand masses, with smooth-floored, almost sand-free basins between them. These sand masses lie in the western part of Libya's vast Marzuq Sand Sea (centered at 24.5 degrees north, 12 degrees east). Geologists think that the draa of the Marzuq were probably formed by winds different from the prevailing north-northeast winds of today.
Numerous smaller dunes have developed on the backs of the draa. Three distinct dune types are visible: longitudinal dunes, which are more or less parallel with the north winds; transverse dunes, which are usually more curved and formed at right angles to the wind; and star dunes, in which several linear arms converge towards a single peak.
The upwind sides of the sand masses appear smoother than the downwind side. Wind is moving sand grains almost all the time. This means that the draa and the dunes are all moving as sand is added on the upwind side and blown off the downwind side. Small sand masses move much faster than large sand masses. The draa are almost stationary, but the smaller dunes move relatively quickly across their backs. When the smaller dunes reach the downwind side of the draa, they are obliterated; their sand is blown across the basins as individual grains.
