STS099-355-24
|
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.
|
STS099-723-54
|
Cyclone with Occluded Front: A thick band of clouds, marking
an occluded front, wraps clockwise around a large, non-tropical
cyclone located southwest of New Zealand.
|
STS099-708-AV
|
Kamchatka Peninsula: Southern Kamchatka Peninsula is at the
junction of three tectonic plates: Eurasian, Pacific, and North
American. Off the southeastern coast of the peninsula lies the deep
(>25,000 ft) Kurile trench, where the Pacific plate is descending
beneath Eurasia as the two converge. In such settings (subduction
zones) volcanoes develop on the overriding plate -- Eurasia in this
instance -- producing the craters, lava flows, and rugged topography
seen in this southward view. Shuttle Radar Topography Mission (SRTM)
images provide great topographic detail for interpreting the
photographic data: (
http://spaceflight.nasa.gov/gallery/images/shuttle/sts-99/html/).
|
STS099-702-45
|
Ethiopian Rift: The Ethiopian rift is a relatively young part
of the vast East African rift system, which stretches from the
Mediterranean coast to Mozambique on the Indian Ocean. Continental
crust is still being pulled apart in this region -- an ocean basin
has not yet formed, as has occurred in the Gulf of Aden and the Red
Sea. Fault-bounded depressions in the rift valley are filled with
lakes (sharp, straight lake shorelines), which are not yet connected
by through-flowing streams. The northernmost is Lake Ziway; Lakes
Langano (east), Abiyata (west), and Shala (south) form the cluster of
three; still farther south is Lake Awasa. Volcanic vents are aligned
along rift-valley faults (dark shield-shaped area in NE); successive
lava flows from such fissure vents eventually build extensive basalt
plateaus, as in the adjacent Ethiopian Highlands.
|
STS099-727-54
|
Northern Rio Grande Rift: The Sangre de Cristo range of
Colorado and New Mexico flanks the southern San Luis valley, one of
the broad valleys of the northern Rio Grande rift. The Rio Grande,
the sinuous dark line roughly parallel to the mountain front, flows
south- then southwestward (this view is to the NE). The southwesterly
reach of the river follows the Embudo transverse fault zone, which
separates the San Luis basin (north) from the Espaņola basin (south).
Rift faults and the Embudo zone intersect in a complex structural
knot around Taos, in the embayment in the mountain range. This
excellent photo shows the subtle but distinct northeastward extension
of the Embudo zone to the mouth of Rio Pueblo canyon at the range
front. Buried faults of similar trend were located geophysically by
astronaut candidate crews who assisted in a ground-water assessment
of the Taos valley (summer, 1999).
|
STS099-729-28
|
Izmit, Turkey -- Earthquake Fault: In August and again in
November, 1999, strong earthquakes rocked the city of Izmit at the
head of the Gulf of Izmit (lighter ground at far right edge of
frame). The fault that ruptured during those events forms the sharp,
straight, southern Gulf shoreline. Another active fault defines the
southeastern shore of Lake Iznik (lower right). Magnitudes were M 7.4
and M 7.1, respectively, and horizontal displacements ranged from 1.5
to 5 m. The North Anatolian fault zone, of which the Izmit fault
is part, marks the boundary between the Eurasian and Anatolian
tectonic plates. Most of Turkey is on the Anatolian plate and is
moving westward with respect to the Black Sea and the rest of
Eurasia. This region is one of high seismicity; during historic
times, earthquake foci have been moving progressively westward,
increasing the risk to population centers such as Istanbul (center of
view).
|
STS099-349-2
|
Airglow: 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.
|
STS099-703-7
|
Socorro Island Wake Cloud Pattern: A distinct cumulus cloud
pattern marks the an island wake within a weak northerly wind field
in the vicinity of Isla Socorro, south of the Baja Peninsula of
Mexico. A smaller companion island, San Benedicto, is visible to the
north-northeast. Socorro rises to just over 3,400 feet and disrupts
the winds which apparently are not strong or persistent enough to
form closed vortices.
|
STS099-714-60
|
Cairo, Egypt: Cairo is one of the fastest growing cities in
the world. The city is moving outside the dark-colored Nile valley
into the surrounding desert. New developments are side by side with
ancient monuments. The pyramids at Giza are highlighted by their
shadows and the new development in the desert to the South is
outlined by lighter-colored roads. Further south of the Giza pyramids
on the west side of the Nile River are the Step and Bent Pyramids,
respectively.
|
STS099-720-14
|
Tenerife, Canary Islands: Tenerife Island, the largest in the
Canary Island archipelago, is approximately 50 miles (80 kilometers)
long and 32 miles (54 kilometers) at its widest point.
|
