The city lights of Spain and Portugal define the Iberian Peninsula in this photograph from the International Space Station (ISS). Several large metropolitan areas are visible, marked by their relatively large and brightly lit areas, including the capital cities of Madrid, Spain - located near the center of the peninsula's interior - and Lisbon, Portugal - located along the southwestern coastline. The ancient city of Seville, visible to the north of the Strait of Gibraltar, is one of the largest cities in Spain. The astronaut view is looking toward the east, and is part of a time-lapse series of images. The blurring of city lights is caused by thin cloud cover (image left and center), while cloud tops are dimly illuminated by moonlight. Though obscured, the lights of France are visible near the horizon line on the upper left, while the lights of northern Africa are more clearly discernable at right. The faint gold and green line of airglow - caused by ultraviolet radiation exciting the gas molecules in the upper atmosphere - parallels the horizon (or Earth limb). The Iberian Peninsula is the southwestern-most of the European peninsulas, bounded by the Atlantic Ocean to the northwest, west, and southwest and the Mediterranean Sea to the east. Its northeastern boundary is marked by the Pyrenees mountain range.