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If the viewing and lighting conditions are ideal, that mirror-like surface can extend over very large areas, such as the entire surface of Lake Ontario (approximately 18,960 square kilometers). This astronaut photograph was taken while the ISS was located over a point to the southeast of Nova Scotia, approximately 1,200 kilometers (740 miles) ground distance from the centerpoint of the image. Lake Ontario, Lake Huron, the Finger Lakes of New York, and numerous other bodies of water appear brilliantly lit by sunglint. To the west, Lake Erie is also highlighted by sunglint, but less light is being reflected towards the astronaut observer, resulting in a duller appearance.
Much of central Canada is obscured by extensive cloud cover in the image, whereas a smaller grouping of clouds obscures the Appalachian range and Pennsylvania (image lower left). The blue envelope of the Earth’s atmosphere is visible above the curved limb, or horizon line, that extends across the upper third of the image. Such panoramic views of the planet are readily taken with handheld digital cameras through ISS viewing ports, which allow the astronaut to take advantage of the full range of viewing angles.
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From space, astronauts documented the first lake—the easternmost one—in 1998. The lakes grew progressively as water flowed further west into each depression, with the westernmost basin filling between 2000 and 2001. The two astronaut photographs above, both taken from the International Space Station, indicate that the lakes were largely depleted by mid-2012, whereas water levels were at their highest in 2002. For scale, the lakes extended 110 kilometers from west to east in 2002.
The more recent image shows lines of center-pivot agricultural fields near the east basin (upper image), which is nearest to Lake Nasser. Sunglint on the western lake makes the water surface appear both light and dark, depending on which parts of the surface were ruffled by the wind at the moment the image was taken.
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The Persian Gulf to the north and northeast is devoid of lights; likewise, the open desert to the south-southeast provides a stark contrast to the well-lit urban and industrial areas. A bright circle of light located within the heavy industrial area (image center) cannot be resolved in this astronaut photograph, but is likely a concentration of lights associated with ongoing processing or construction activities. The approximate scale of the feature—100s of meters in diameter—is consistent with multiple stationary light sources, particularly if the light from those sources is accentuated due to the camera’s low light settings.
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On June 13, 2012, when this image was taken from the ISS as it passed over the Tibetan Plateau, polar mesospheric clouds were also visible to aircraft flying over Canada. In addition to the still image above, the ISS crew took a time-lapse image sequence of polar mesospheric clouds several days earlier (June 5) while passing over western Asia. It is first such sequence of images of the phenomena taken from orbit.
Polar mesospheric clouds form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface when there is sufficient water vapor at these high altitudes to freeze into ice crystals. The clouds are illuminated by the Sun when it is just below the visible horizon, lending them their night-shining properties. In addition to the polar mesospheric clouds trending across the center of the image, lower layers of the atmosphere are also illuminated. The lowest layer of the atmosphere visible in this image—the stratosphere—is indicated by dim orange and red tones near the horizon.
While the exact cause for the formation of polar mesospheric clouds is still debated—dust from meteors, global warming, and rocket exhaust have all been suggested as contributors—recent research suggests that changes in atmospheric gas composition or temperature has caused the clouds to become brighter over time.
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Much of the sea surface surrounding the volcano has a silver-gray appearance. This mirror-like appearance is due to sunglint, where light reflects off the sea surface and is scattered directly towards the observer on the International Space Station. Sunglint is largely absent from a zone directly to the west of the volcano, most likely due to surface wind or water currents that change the roughness—and light scattering properties—of the water surface. (Note that the image is oriented so that north is to the lower left.)
Volcanoes in the Kurils and similar island arcs in the Pacific “ring of fire”, are fed by magma generated along the boundary between two tectonic plates, where one plate is being driven beneath the other (a process known as subduction). Alaid Volcano has been historically active, with the most recent confirmed explosive activity in 1996.
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Water in the marsh takes on different colors—from brown to pink to light green, moving northeast to southwest—as a result of the interplay of water depth and the resident organisms such as algae. Algae color varies depending on water temperature and salinity.
Irregular gray areas (top left) are wet zones between low sand dunes. These inter-dune flats are whitened with salt that comes from the evaporation of Caspian Sea water. (The Sea is just beyond the top left of the image.) The jagged line following the colored water is the limit of the wetting zone (or perimeter), an irregular zone influenced by wind and the depth of water in the marsh.
Small cliffs mark the eastern margin of the depression that contains Sor Kaydak. Above the cliffs, a plateau—about 200 meters above the salt marsh, 160 meters above global sea level—extends eastward for hundreds of kilometers. Here the plateau is occupied by a dense pattern of well heads, which appear as a geometric pattern of tan dots. By contrast, the west margin (image left) rises less than 10 meters above the marsh.
The straight line visible at image center is a pipeline built to take oil to a terminal on the Caspian shore 100 kilometers northwest of the area shown here.
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Astronaut Don Pettit, flight engineer for International Space Station (ISS) Expedition 31, was particularly keen to take photos of the event from orbit—even bringing a solar camera filter aboard for the event. This top image, from the first half of the 2012 transit, is one of hundreds taken from the ISS Cupola, a windowed module that provides the crew with unparalleled views of both Earth and astronomical phenomena. In fact, history will record the ISS as the first orbital, crewed spacecraft from which the Transit of Venus has been observed. In addition to the dark circle of Venus visible at image upper left, several smaller sunspots are visible at image center.
The eight-image series (lower) comes from one of those solar-observing spacecraft: NASA’s Solar Dynamics Observatory (SDO). The full-disk images were captured between 21:00 Universal Time on June 5 and 06:00 UTC on June 6 by the Helioseismic and Magnetic Imager (HMI), an instrument designed to study the oscillations and magnetic field of the solar surface, or photosphere. As with Pettit’s photo, HMI reveals several sunspots near the middle of the Earth-facing side of the Sun, as well as the larger, transient disk of Venus in the upper third of the images. A movie showing the entire Transit is available for download by clicking on the link below the image or by visiting our YouTube channel. The SDO team also produced a montage of high-definition views of the Transit that you can see here.
The Transit of Venus in front of the Sun is one of only two such planetary crossings—the other being the Transit of Mercury—that are visible from Earth. While transits of Mercury occur thirteen times each century, Venus transits the Sun only twice over the same time period. (The first transit of the current pair occurred in 2004). Unless you are fortunate enough to be at locations where the transit is visible both times, this makes the Transit of Venus a true “once in a lifetime” event.
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The so-called linear dunes—shown here in the Great Sand Sea of southwest Egypt—are easily spotted from space, and local maps show that they rise 20 to 30 meters above the surrounding plains. The distance between dunes is interestingly regular, at 1.5 to 2.5 kilometers, suggesting some equilibrium exists between the wind strength and the sand supply. It is possible that the linear dunes are a reflection of earlier times, when winds were stronger or sand more plentiful.
The dark rock outcrops at image lower left stand above the surface by as much as 150 meters. North winds have been deflected around this high zone, and smaller secondary linear dunes appear along the left side of the image, aligned with local winds that become ever more northeasterly as they approach the outcrops. A dune-free zone on the protected downwind (south-southeast) side of the outcrop gives a sense of the sand movement.
At first glance, the large linear dunes appear to be the major landform in the image; however, a complex pattern of even smaller dunes can be seen on top of the largest dunes (inset). It is not uncommon to observe multiple dune forms in large sand seas, as in the Marzuq Sand Sea, the Ar Rub' Al Khali, and the Tenere Desert.
The sand in many dune fields usually derives from some larger river not very distant upwind; often it comes from a dry river bed that gets exposed to wind during dry seasons, or from a low-flow river that changed due to a more arid regional climate. Inland dune fields thus lie downwind of the source river. West of the dunes shown in this photograph, a large, unnamed river once flowed to the Mediterranean Sea and dumped its sand load 300 kilometers northwest of the area shown. It is likely that this river—evidence of which is now almost completely obliterated—was the source of the sand in the linear dunes.
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Bands of relatively low-altitude cumulus clouds appear like a flotilla of ships, with west-facing sides illuminated by waning sunlight and the rest of the clouds in shadow. Due to the low Sun angle, the clouds cast long and deep shadows over large swaths of the ocean. Given the short camera lens used, an individual cloud shadow may extend for miles. Light gray clouds at image lower left appear to be at a higher altitude. The cloud cover is likely a remnant of a frontal system that moved in from the Pacific and over inland South America a day or two prior to when the image was taken.
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Lake Powell is part of the Glen Canyon National Recreation Area, which extends for more than 300 kilometers (186 miles) along the shoreline and side canyons. The primary intended use of Lake Powell’s water is support for agriculture, with a small portion allocated to urban use in Arizona, Nevada, and California.
The reservoir did not reach its maximum capacity of 27 million acre-feet until 1980. More recently, extended drought conditions in the southwestern United States have resulted in a significant lowering of the lake water level and the emergence of formerly submerged parts of Glen Canyon. Should average precipitation in the Colorado River watershed decrease (as predicted by regional climate change models), that could result in further lowering of Lake Powell and changes to the water management plans.
Fluctuations in water levels and changes in river courses are a common occurrence in the geologic record of rivers. Looking somewhat like a donut or automobile tire from the vantage point of the International Space Station, The Rincon (image center) is an entrenched and abandoned meander, or loop, of the Colorado River. Scientists believe it formed several thousand years ago when the river cut straight across the ends of the loop and shortened its course by six miles. The resulting canyon and 600 to 750 feet-high central mesa indicate where the river used to flow.
The term “rincon” also is used by geomorphologists to describe similar ancient river features observed elsewhere. The Goosenecks of the San Juan River are an example of an active entrenched meander.
