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The shortest distance between two points on the earth's surface is along a great
circle. With the exception of the Equator, a great circle intersects all other
meridians at different angles.
9.4.2.2 Small circles
All circles that are not great circles are small circles (i.e. small circles). Small
circles are characterized by the fact that they do not divide a sphere into two
equal parts.
All parallels except the Equator are thus small circles.
9.4.2.3 Compass lines
A line on the surface of the earth that intersects the meridians at the same angle
is called a compass line (rhumbline or R/L).
A compass line will form a spiral that will end close to the poles.
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The exceptions are, however, angles of intersection of 90 and 270 , which will
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coincide with the parallels, and the angles of intersection of 180 and 360 , which
coincide with the meridians.
The drawing shows a compass line (red) and a great circle (blue) and associated
red and blue angles.
The red angles that go from the compass line (the red arc) to the meridians (the
gray lines) are everywhere the same
size.
The blue angles that go from the great
circle (the blue line) to the meridians
have different sizes, which is due to the
meridians converging (approaching each
other) towards the poles.
Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 820
