Terra incognita refer to the hypothesized continent Terra Australis Incognita ("The unknown land of the South"), as seen in the Theatrum Orbis Terrarum map by Abraham Ortelius (1570). During the 19th century "terra incognita" disappeared from maps of the earth, since both the coastlines and the inner parts of the continents had been fully explored. But the bottoms of the seas remain mostly un-mapped, as do many other land surfaces in the solar system. The phrase is now also used metaphorically by various researchers to describe any unexplored subject or field of research. For more history of the terms, see Terra Australis,
Sagan Planet Walk Sagan, Bill Nye, narrated a podcast tour of the Planet Walk in 2006 which can be accessed free by calling 703.637.6237 as you walk through the scale-model representation of the Solar System. The models of the Solar System, in order: The Sagan Planet Walk has inspired the creation of other scale-model Solar Systems in the United States. Sagan Planet Walk The Sciencenter's Sagan Planet Walk is a walkable scale model of the Solar System, located in Ithaca, New York. The model scales the entire Solar System—both planet size and distances between them—down to one five billionth of its actual size.