Earth's Magnetic Poles - Windows to the Universe
Geographic north and south poles are determined by the earth's spin. Magnetic variance, or declination, is the difference between geographic north and. Info about the geographic and magnetic North Pole. navigation to be keenly aware of the difference between Magnetic North and True North. The earth acts as a giant magnet with the poles close to where our axis of rotation The difference between Magnetic North and Geographic North is important if.
Each level curve is an isogonic line. NIMA Magnetic Variation Map The magnetic declination in a given area may most likely will change slowly over time, possibly as little as 2—2.
Why does a magnetic compass point to the Geographic North Pole?
This may be insignificant to most travellers, but can be important if using magnetic bearings from old charts or metes directions in old deeds for locating places with any precision. As an example of how variation changes over time, see the two charts of the same area western end of Long Island Soundbelow, surveyed years apart.Earth's Magnetic Field Explained - Terrestrial Magnetism - Science - Elearnin
The chart shows a variation of 8 degrees, 20 minutes West. The chart shows 13 degrees, 15 minutes West. Direct measurement[ edit ] Antique declinometer The magnetic declination at any particular place can be measured directly by reference to the celestial poles —the points in the heavens around which the stars appear to revolve, which mark the direction of true north and true south. The instrument used to perform this measurement is known as a declinometer.
The approximate position of the north celestial pole is indicated by Polaris the North Star.
Geographic and Magnetic Poles
In the northern hemisphere, declination can therefore be approximately determined as the difference between the magnetic bearing and a visual bearing on Polaris. Polaris currently traces a circle 0. At high latitudes a plumb-bob is helpful to sight Polaris against a reference object close to the horizon, from which its bearing can be taken. Isogonic lines are also shown on aeronautical and nautical charts.
Remember, swirling motions of molten metal in Earth's outer core make our planet's magnetic field. Those swirling motions are changing all the time.
That means the magnetic field is changing, so the magnetic poles move! In the first part of the 20th century, the poles usually moved about 9 km 5. Then, aroundthey started moving faster. In recent years they have been moving about 41 km 25 miles per year! Sometimes Earth's magnetic field even flips over! The North and South Magnetic Poles trade places.
This doesn't happen very often; usually at least a few hundred thousand years pass between these flips. Speaking of flipping, did you know that Earth's North Magnetic Pole is actually a south pole? When compasses were first invented, people noticed that one end of the compass pointed towards the North. They called the end of the compass needle that pointed North the "north end" of the needle makes sense! Later, people learned more about magnets. They learned that like ends a north and a north OR a south and a south push away from each other.
They learned that opposite ends such as a north and a south pull toward each other.
What's the Difference Between the Geographic and Magnetic North Poles?
The needle of a compass is a tiny bar magnet. Earth's magnetic field shifts over timeeventually completely reversing its polarity.
There is evidence in magnetic mineral orientation that, during the past 10—15 million years, reversals have occurred as frequently as every quarter million years. Although Earth's magnetic field is subject to constant change periods of strengthening and weakening and the last magnetic reversal occurred approximatelyyears ago, geophysicists assert that the next reversal will not come within the next few thousand years. The present alignment means that at the northern magnetic pole, a dip compass a compass with a vertical swinging needle points straight down.
At the southern magnetic pole, the dip compass needle would point straight up or away from the southern magnetic pole.
Magnetic North Pole vs. Geographic North Pole
The magnetic poles are not stationary and undergo polar wandering. The north magnetic pole migrates about 10 km per year. The magnetic reversals mean that as igneous rocks cool from a hot magmathose that contain magnetic minerals will have those minerals align themselves with the magnetic polarity present at the time of cooling.