Pyramids at Giza
Pyramids at Giza. Satellite image of the three pyramids at Giza, in northern Egypt. The pyramids are thought to have been built between 2600 and 2500 BC, as tombs and monuments for members of the ruling dynasties of ancient Egypt. The largest pyramid (lower left) was built for King Khufu, or Cheops. Its construction is thought to have taken over 20 years, and for many centuries it was the tallest building in the world. The pyramid at centre right was built for King Khafre, son of Khufu. The smallest pyramid (upper right) was built for King Menkaure. The pyramids at Giza are the only one of the Seven Wonders of the World still intact.
© SPACE IMAGING EUROPE/SCIENCE PHOTO LIBRARY
Mayan temple at night. This is El Castillo (the castle), part of the Mayan city of Chichen Itza in Yucatan, Mexico. This structure stands at 22 metres high. The construction of this pyramid was planned so that during the spring equinox (around 21 March), the setting sun casts a shadow of a snake writhing down the pyramid's steps. The Maya were Native American people, originating in Yucatan around 2600 BC. They developed astronomy, calendrical systems and hieroglyphic writing from the ideas of earlier civilizations. Mayan civilization went into decline in AD 900 and came to a close in AD 1200.
© TONY CRADDOCK/SCIENCE PHOTO LIBRARY
Decision making. Conceptual computer artwork of a hierarchy of decision makers, showing a lower level of 25 brains, which pass their decisions to a middle level of nine brains, which in turn pass the information to the top brain. Many hierarchical systems are arranged in a similar manner, and similar patterns are seen in many natural phenomena, such as food chains.
© LAGUNA DESIGN/SCIENCE PHOTO LIBRARY