In the era of smart phones with GPS and Google Maps, you're probably already familiar with the system of geographic coordinates that's commonly used to describe locations on the Earth's spherical surface. That system is based on latitude, the distance north or south from the Earth's equator, and longitude, which is the distance east or west of the Prime Meridian, an imaginary line that runs north to south through Greenwich, England. The distances are measured in degrees — 90 degrees in each direction for latitude, and 180 in each direction for longitude — and minutes, seconds and fractions of a second. (For more on how that system works, check out these pages from the U.S. Geological Survey and the IBM Knowledge Center.) … [Read more...] about How Do We Find Things in the Blackness of Space?