Observations of the planet Venus include those in antiquity, telescopic observations, and from visiting spacecraft. Spacecraft have performed various flybys, orbits, and landings on Venus, including balloon probes that floated in the atmosphere of Venus. Study of the planet is aided by its relatively close proximity to the Earth, compared to other planets, but the surface of Venus is obscured by an atmosphere opaque to visible light. Historical observations and impact As one of the brightest objects in the sky, Venus has been known since prehistoric times, and as such, many ancient cultures recorded observations of the planet. A cylinder seal from the Jemdet Nasr period indicates that the ancient Sumerians already knew that the morning and evening stars were the same celestial object. The Sumerians named the planet after the goddess Inanna, who was known as Ishtar by the later Akkadians and Babylonians. She had a dual role as a goddess of both love and war, thereby representing a deity that presided over birth and death. One of the oldest surviving astronomical documents, from the Babylonian library of Ashurbanipal around 1600 BC, is a 21-year record of the appearances of Venus. Because the movements of Venus appear to be discontinuous (it disappears due to its proximity to the sun, for many days at a time, and then reappears on the other horizon), some cultures did not immediately recognize Venus as single entity; instead, they assumed it to be two separate stars on each horizon: the morning star and the evening star. The Ancient Egyptians, for example, believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti. The Ancient Greeks called the morning star , (Latinized Phosphorus), the "Bringer of Light" or , (Latinized Eosphorus), the "Bringer of Dawn". The evening star they called (Latinized Hesperus) (, the "star of the evening"). By Hellenistic times, the ancient Greeks identified it as a single planet, which they named after their goddess of love, Aphrodite (), Phoenician Astarte, a planetary name that is retained in modern Greek. Hesperos was translated into Latin as Vesper and Phosphoros as Lucifer ("Light Bearer"). Venus was considered the most important celestial body observed by the Maya, who called it Chac ek, or Noh Ek', "the Great Star" and Xux Ek', the Wasp Star. The Maya based their religious calendar partially upon the movements of Venus and