about angle between magnetic axis and geographical axis of earth How the angle between the magnetic axis of earth and the geographic axis of earth can be calculated?
 A: The magnetic axis of the Earth is defined as the axis of the closest fitting magnetic dipole to Earth's magnetic field. 
The magnetic field of the Earth is not exactly a dipole, it is even asymmetric between the Northern hemisphere and the southern hemisphere: the North magnetic pole is located at 86.27°N and the South magnetic pole at 64.26°S. Moreover, they move over time.
However, Earth's magnetic field can be approximated to the first order by a dipole. (You can get a higher order expansion by adding higher orders: a quadrupole, an octupole... This is what the IGRF model does). The two positions where the the axis of this dipole crosses the surface are called the geomagnetic poles. These are located at 80.31°N and 80.31°S.
The geographical axis (or rotational axis) crosses the surface of the Earth, by definition of geographical latitude at 90°N and 90°S. Thus the angle between the magnetic dipole axis of the Earth and the geographic axis is thus 90°-80.31° = 9.69°.
A: To calculate the angle between them you subtract the latitude of magnetic north from the latitude of axial north. Note though that magnetic north moves around on Earth's surface so there's no way to figure out where it is to begin with except by walking around with a compass until you find it (or some technologically advanced equivalent).
