What is Longitude and Latitude

Any location on Earth is described by two numbers--its latitude and its longitude. If a pilot or a ship's captain wants to specify position on a map, they would use these "coordinates". Actually, these are two angles, measured in degrees, "minutes of arc" and "seconds of arc." These are denoted by the symbols (?, ', ") e.g. 35? 43' 9" means an angle of 35 degrees, 43 minutes and 9 seconds (do not confuse this with the notation (', ") for feet and inches!). A degree contains 60 minutes of arc and a minute contains 60 seconds of arc--and you may omit the words "of arc" where the context makes it absolutely clear that these are not units of time. Calculations often represent angles by small letters of the Greek alphabet, and that way latitude will be represented by ? (lambda, Greek L), and longitude by ? (phi, Greek F).

Longitude shows your location in an east-west direction, relative to the Greenwich meridian. Places to the east of Greenwich (such as Middle East, India and Japan) have longitude angles up to 180 degrees east. Places to the west of Greenwich (such as the Atlantic and North and South America) have angles up to 180 deg west. For inputting to the satellite dish pointing calculator, longitude west figures need to be input as negative numbers.

Geostationary satellites are located in orbit directly above the equator and stay in the same place in the sky since they go around the earth at the same angular speed as that of the earth as it rotates. Satellite locations may thus be defined by longitude only. The use of east and west longitudes is popular for public use since the numbers are smaller. Use of degrees east only (0 to +360 deg, going east from Greenwich) however is my preference since the satellites go around this way and it makes sense for the numbers to keep increasing if the satellite moves forwards. Trying to do orbit calculations is bad enough without having numbers that keep switching forwards and backwards. Many satellite operators also use the 0 to +360 deg method, but may additionally provide the "deg west" notation for some output publications.

The vertical longitude lines are also known as meridians. They converge at the poles and are widest at the equator (about 69 miles or 111 km apart). Zero degrees longitude is located at Greenwich, England (0?). The degrees continue 180? east and 180? west where they meet and form the International Date Line in the Pacific Ocean. Greenwich, the site of the British Royal Greenwich observatory was established as the site of the prime meridian by an international conferencing 1884.The vertical line can be seen when looking at a map.

When looking at a map, latitude lines run horizontally. Latitude lines are also known as parallels since they are parallel and are an equal distant from each other. Each degree of latitude is approximately 69 miles (111 km) apart; there is a variation due to the fact that the earth is not a perfect sphere but an oblate ellipsoid (slightly egg-shaped). To remember latitude, imagine them as the horizontal rungs of a ladder ("ladder-tude"). Degrees latitude are numbered from 0? to 90? north and south. Zero degrees are the equator, the imaginary line that divides our planet into north and south poles.