Geocentric model explanation in terms of the Earth's revolution about the sun. In 1838, astronomer Friedrich Wilhelm Bessel measured the parallax of the star 61 Cygni successfully, and disproved Ptolemy's claim that parallax motion did not exist. This finally confirmed the assumptions made by Copernicus, providing accurate, dependable scientific observations, and conclusively displaying how distant stars are from Earth. A geocentric frame is useful for many everyday activities and most laboratory experiments, but is a less appropriate choice for solar system mechanics and space travel. While a heliocentric frame is most useful in those cases, galactic and extragalactic astronomy is easier if
National Register of Historic Places listings in Central Baltimore National Register of Historic Places listings in Central Baltimore This is a list of National Register of Historic Places properties and districts in downtown Baltimore, Maryland, United States. Many other properties are located in other parts of the city; for these, see National Register of Historic Places listings in Baltimore, Maryland. The locations of the National Register properties and districts listed below (at least for all showing latitude and longitude coordinates below) may be seen in a map by clicking on "Map of all coordinates". Much of the central portion of the city and significant portions of the waterfront and