|
| quote: | Originally posted by eckmek
true North? |
From Wiki:
| quote: |
True north is compared to magnetic north (the direction of the magnetic north pole) and grid north (the direction northwards along the grid lines of a map projection).
The direction of true north is marked in the skies by the north celestial pole. For most practical purposes, this is the position of Polaris. However, due to the precession of the Earth's axis, true north rotates in an arc that takes approximately 25,000 years to complete. In 2002, Polaris was at its closest approach to the celestial north pole. 2,000 years ago, the closest star to the celestial north pole was Thuban.
On maps issued by the United States Geological Survey, and the U.S. military, true north is marked with a line terminating in a five-pointed star. Maps issued by the Ordnance Survey contain a diagram showing the difference between true north, grid north and magnetic north at a point on the sheet.
|
This is known as declination. Any decent topographical map will have a declination chart, allowing you to calculate how far off the North marked on the map the Earth has moved. Something like 'Annual change decreasing 2 degrees, 6 minutes.....etc'.
Doesn't seem like a huge deal, and over short distances it's not, but a 1 degree change in vector over 100m will put you off target by 1m. If you are hiking 100kms, that 1 degree change puts you well away from your intended photo op.
___________________
If you can't be good, be careful.
"Hey look, I can make a heart-shape with my hands!!!" So Fucking what? Stop it. You're a douche.
When life gives you lemons, squirt the juice in the eyes of your enemies.
|