How does a compass always point to due north?
"Due North," by definition, is the direction towards the earth's north pole; or, visually at night, towards Polaris, the north star. Therefore, compasses generally do NOT point towards due North but, rather, point towards "magnetic north," as the other responder described, which is a variably located at some distance from True North, depending upon where the north-locating compass is situated on our planet. In most circumstances magnetic North is close enough so that people are willing to accept it as North in general terms. However, depending on your location, and upon seasonal changes caused by Earth's wobbling rotation (called precession) true North can be many degrees off from magnetic (from your compass's) North. In those cases true North must be determined using declination charts, which will tell you how many degrees to add or subtract on you compass in order to determine true North by the Magnetic North your compass is pointing to. For example, if magnetic North is 10 degrees west of true North at your compass's location (that is, your compass is actually pointing 10 degrees to the "left" of North), then you would correct by considering the +10-degree bearing point on your compass dial as True North--and, likewise, add 10 degrees to any bearing line you happen to determine using your compass. You have one other way of finding True North, which is celestially, by sighting towards the Pole star, aka Polaris, aka the North Star...that is, providing that the sky is UNcloudy and unsunny enough for the star to be visible. Of course, that only works for those located in the morthern hemisphere. Those south of the equator have a "south pole" star but it is not as accurate as Polaris in the northern hemisphere.
Jul 09, 2012 |
Camping, Backpacking & Hiking