Convergence and Conversion Angle – Ibex Aviation Academy

Convergence Conversion angle

Convergency or Earth convergence is the angular difference between two meridians at a parallel of latitude
Meridians converge towards the poles and diverge towards the equator
At the equator, two meridians with 45 degrees of difference in longitude are parallel to each other
Angular difference between the meridians is zero
At the poles, the same two meridians with 45 degrees of difference in longitude are have an angle of 45 degrees
Angular difference is same as their change in longitude
At any other latitude, the same two meridians with 45 degrees of difference in longitude are have an angle of between 0 and 45 degrees
The angular difference between two meridians at a given latitude is called as Earth Convergence or Convergency
Convergence is minimum at 0 degrees latitude and maximum at 90 degrees latitude
Therefore, we can say that the convergency follows a sine curve
At equator or 0 degrees latitude, Sin 0 is equal to 0
At poles or 90 degrees latitude, Sin 90 is equal to ch-long
The formula for convergency is therefore given by a formula
Convergency = ch-long x sine (lat)

Convergency signifies the change in great circle track direction
Convergency is the angle of inclination between two selected meridians
The value of change in the great circle track is same as convergency at that latitude
If the points are not on the same latitude their mid-meridian is considered for calculation

Conversion angle is the difference between Great circle and Rhumb line tracks
Conversion angle is equal to half of convergency since Rhumb line is a uniformly curved line
The value of variation between Great Circle and Rhumb Line Track is given by Conversion Angle
Therefore, formula for conversion angle is given by a formula
Conversion angle = ½ ch-long x sine mean lat