ISS033-E-22378 Click the photo number to access all resolutions available and the database record.
Sunglint reflections reveal details of Chesapeake Bay and the great bend of the Potomac River. Cities are difficult to detect from space during daylight hours, so the sickle-shaped bend of the river is a good visual guide for astronauts trying to photograph the nation’s capital, Washington D.C. The farm-dominated Piedmont Plateau is the light-toned area between the mountains and the bay.
The Appalachian Mountains appear striped because the ridges are forested, providing a dense and dark canopy cover, while the valleys are farmed with crops that generally appear as lighter-toned areas. (Farmland is even lighter than usual in this image because the fields are fallow after the harvest.) Geologically, the valleys are the softer, more erodible rock layers, much the preferred places for human settlement. Not only do the larger rivers occupy the valley floors, but the soils are thicker, the slopes are gentler, and the valleys are better protected from winter winds.
The rocks that form this valley-and-ridge province, as it is known, are relatively old (540 to 300 million years old) and were laid down in horizontal layers when North America was attached to Europe in the ancient supercontinent of Laurasia. During this time Gondwanaland—an ancient supercontinent that included present-day Africa, India, South America, Australia, and Antarctica—was approaching Laurasia under the influence of plate tectonics. The northwest coastline of modern Africa was the section of Gondwanaland that “bumped up” against modern North America over a long period (320 to 260 million years ago).
The net result of the tectonic collision was the building of a major mountain chain, much higher than the present Appalachian range. In the process, the flat-lying rock layers were crumpled up into a series of tight folds, at right angles to the advance of Gondwanaland. The collision also formed the singular supercontinent of Pangaea. Over the following 200 million years, Pangaea broke apart; the modern Atlantic Ocean formed; and erosion wore down the once-high mountains. What is left 200 million years later are the coastline of North America and the eroded stumps of the relatively low, but visually striking mountain chain.
ISS033-E-21663=Dallas Metropolitan Area at Night: Most metropolitan areas of the western United States are spread over large areas with regular street grid patterns that are highly recognizable from space (particularly at night). The northern Dallas metro area in Texas exhibits this pattern in this astronaut photograph from the International Space Station.The north-south and east-west grid of major streets is highlighted by orange lighting, which lends a fishnet-like appearance to the urban area. Smaller residential and commercial buildings give green-gray stipple patterns to some blocks. The airplane terminals of Dallas-Fort Worth International Airport are lit with golden-yellow lights and surrounded by relatively dark runways and fields. Likewise, the runways of Dallas Love Field are recognizable by their darkness.
Other dark areas within the metro region are open space, parks, and water bodies. Larger commercial areas, as well as public and industrial facilities, appear as brilliantly lit regions and points. For comparison, a day-time view of Dallas is available here.
Dallas is part of the larger Dallas-Fort Worth-Arlington Metropolitan Statistical Area (population 6,526,548 in 2011), as recognized by the U.S. Census Bureau. To most Texans, it is simply “DFW” or “the Metroplex.” Several of the larger urban areas within DFW are visible in this image; Dallas, Garland, and Richardson all have populations above 100,000 according to the North Central Texas Council of Governments. While the economy of Dallas was historically based in the oil and cotton industries, today commerce, technology, healthcare, and transportation are the major economic drivers.
