Seen here is the triangular shadow cast by Mount Teide, a volcano on Tenerife in the Canary Islands. With a summit of 3,718-metre (12,198 ft) it is the highest point in Spain and the highest point above sea level in the islands of the Atlantic. At 7,500 m (24,600 ft) from its base on the ocean floor, it is the third highest volcano in the world, after Mauna Kea and Mauna Loa in Hawaii. Its elevation makes Tenerife the tenth highest island in the world.

As for why the shadow looks like a triangle when Mount Teide itself does not have a strictly pyramidal shape, APOD explains:

“The triangle shadow phenomena is not unique to the Mt. Teide and is commonly seen from the tops of other large mountains and volcanoes. A key reason for the strange dark shape is that the observer is looking down the long corridor of a sunset (or sunrise) shadow that extends to the horizon. Even if the huge volcano were a perfect cube and the resulting shadow were a long rectangular box, that box would appear to taper off at its top as its shadow extended far into the distance, just as parallel train tracks do.”

 

The volcano and its surroundings comprise Teide National Park, which has an area of 18,900 hectares (73 sq mi) and was named a World Heritage Site by UNESCO on June 29, 2007. It is one of the most visited National Parks in the world, with a total of 2.8 million visitors. [Source]

The World At Night (TWAN) is an international effort to present stunning nightscape photos and time-lapse videos of the world’s landmarks against celestial attractions. The eternally peaceful night sky looks the same above symbols of all nations and regions, attesting to the truly unified nature of Earth as a planet rather than an amalgam of human-designated territories.