Architecture

# Why Are Lines Of Longitude Not Parallel To Each Other? Why Are Longitudes Not Parallel Like Latitudes

Why longitudes are not parallel and why do they meet at the poles? What problem would have happened if like latitudes they were parallel circles running from west to east?I would request the explainer to use a layman”s language with no technical words.

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The meridians correspond to the natural fact that the sun reaches the zenith once a day simultaneously for a set of points that form a straight line from one pole to the other, cutting the equator in a right angle. So meridians are not just artificial lines, but correspond somehow to a natural aspect, something that can be measured. Even with your bare eye, without any instrument, you can observe what time of the day it is right now. If you would collect this information for a given moment from people at diferent places all over the world, you could roughly say how much to the east or west of your point of observation every reporting observer is placed.

Compare with time-zones, they are slices from north to south pole, indicating how much to the east or west of a conventionally definned line they are located. If longitude were parallel circles, you would have different points on the same longitude with different day-time (somewhere midday, somewhere else morning). Such circles have no corresponding phenomenon in nature and thus are pure conventional lines, very difficult to measure (at least in pre-modern times).However, historically it was very difficult to find adequate ways to measure longitude, even with the meridian system. Time was critical to find longitude. Until the 18th century, on ships on the ocean, it was almost impossible to determine exact longitude. There were no clocks that ran exact enough. Longitude is defined as the (angular) distance (in degrees or daytime) form a pre-defined meridian. It took quite an effort (and many sunken ships) to be able to determine longitude accordingly (latitude in contrast was relatively easy to measure on a ship with a sextant and other tools).

So think again: if it was almost impossible to measure longitude from natural phenomenon (like sun and stars), it would have been even more difficult to measure conventional, parallel circles (that you propose) that do not represent any natural phenomenon. So there is some reason for the tradition. Parallel lines for measuring longitude instead would have no real advantage.

For more information, do an internet search for “finding longitude” or “history of longitude”, there are also some good videos out there that explain everything in detail with vivid animations.