The most famous pyramids are the Egyptian pyramids — huge structures built of brick or stone, some of which are among the world’s largest constructions. They are shaped as a reference to the rays of the sun. Most pyramids had a polished, highly reflective white limestone surface, to give them a shining appearance when viewed from a distance. The capstone was usually made of hard stone – granite or basalt – and could be plated with gold, silver, or electrum and would also be highly reflective. After 2700 BC, the ancient Egyptians began building pyramids, until around 1700 BC. The first pyramid was erected during the Third Dynasty by the Pharaoh Djoser and his architect Imhotep. This step pyramid consisted of six stacked mastabas. The largest Egyptian pyramids are those at the Giza pyramid complex. “The Egyptian sun god Ra, considered the father of all pharaohs, was said to have created himself from a pyramid-shaped mound of earth before creating all other gods. The pyramid’s shape is thought to have symbolized the sun’s rays”(Donald B. Redford, Ph.D., Penn State).
The age of the pyramids reached its zenith at Giza in 2575–2150 BC. Ancient Egyptian pyramids were in most cases placed west of the river Nile because the divine pharaoh’s soul was meant to join with the sun during its descent before continuing with the sun in its eternal round. As of 2008, some 135 pyramids have been discovered in Egypt. The Great Pyramid of Giza is the largest in Egypt and one of the largest in the world. It was the tallest building in the world until Lincoln Cathedral was finished in 1311 AD. The base is over 52,600 square metres (566,000 sq ft) in area. While pyramids are associated with Egypt, the nation of Sudan has 220 extant pyramids, the most numerous in the world. The Great Pyramid of Giza is one of the Seven Wonders of the Ancient World. It is the only one to survive into modern times. The Ancient Egyptians covered the faces of pyramids with polished white limestone, containing great quantities of fossilized seashells. Many of the facing stones have fallen or have been removed and used for construction in Cairo.
The ancient pyramids of Egypt
Most pyramids are located near Cairo, with only one royal pyramid being located south of Cairo, at the Abydos temple complex. The pyramid at Abydos, Egypt were commissioned by Ahmose I who founded the 18th Dynasty and the New Kingdom. The building of pyramids began in the Third Dynasty with the reign of King Djoser. Early kings such as Snefru built several pyramids, with subsequent kings adding to the number of pyramids until the end of the Middle Kingdom.
The last king to build royal pyramids was Ahmose with later kings hiding their tombs in the hills, such as those in the Valley of the Kings in Luxor’s West Bank. In Medinat Habu, or Deir el-Medina, smaller pyramids were built by individuals. Smaller pyramids were also built by the Nubians who ruled Egypt in the Late Period, though their pyramids had steeper sides.A pyramid (from Greek: πυραμίς pyramis) is a structure whose outer surfaces are triangular and converge to a single point at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilateral, or any polygon shape. As such, a pyramid has at least three outer triangular surfaces (at least four faces including the base)
Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. The Milky Way is a barred spiral galaxy with a diameter between 100,000 light-years and 180,000 light-years.The Milky Way is estimated to contain 100–400 billion stars. There are probably at least 100 billion planets in the Milky Way. The Solar System is located within the disk, about 26,000 light-years from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars in the inner 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole.
The Milky Way can be seen as a hazy band of white light some 30 degrees wide arcing across the sky. Although all the individual naked-eye stars in the entire sky are part of the Milky Way, the light in this band originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where light from distant stars is blocked by interstellar dust. The area of the sky obscured by the Milky Way is called the Zone of Avoidance.The Milky Way does not sit still, but is constantly rotating. As such, the arms are moving through space. The sun and the solar system travel with them. The solar system travels at an average speed of 515,000 miles per hour (828,000 kilometers per hour). Even at this rapid speed, the solar system would take about 230 million years to travel all the way around the Milky Way.