True Meridian vs Magnetic Meridian
A great circle, which passes through true north and true south is known as meridian. A circle described by the intersection of the surface of the earth with the plane passing through the centre of the earth is known as great circle. That is, great circle is a circle traced on the surface of a sphere (earth is considered as a sphere) such that, both have the same diameter. The 0 degree meridian is known as the prime meridian, from which other meridians or lines of longitude are measured, that passes through Greenwich England. The direction given by the acute angle between a line and a meridian is known as bearing.
The direction from any point along a meridian towards the North Pole of the earth is defined as true north. That is, the north according to the earth’s axis. True north is also known as geographic north. True south is also defined in a similar manner. True meridian is defined as the plane that passes through true north poles and true south poles at the place of observation. True meridian can be established by astronomical observation as it passes through true north and south. True bearing is the horizontal angle between true meridian and a line.
The magnetic north is the direction indicated by a freely suspended and balanced magnetic needle. Magnetic meridian is the line that is parallel to the direction taken by a freely moving magnetized needle. The angle between magnetic meridian and true meridian is known as magnetic declination. A line having zero declination is known as Agonic line. The lines that have the same declination are known as Isogonic lines. Magnetic bearing is the horizontal angle between magnetic meridian and a line.
What is the difference between True Meridian and Magnetic Meridian?
¤ True meridians are fixed, whereas magnetic meridians vary with time and location.
¤ True meridian may be established by astronomical observation, while magnetic meridian can be formed using freely moving magnetized needle.
¤ True meridian passes through the center of the north and south poles, but not necessarily, in case of magnetic meridians.