Circles On The Earth

Question 1

What is a great circle?

Answer 1

Most direct route between 2 points

Question 2

Anti-podal situated

Answer 2

2 positions separated by 180 degrees longitude. They are anti podal situated on the opposite sides of the Earth and in opposing hemisphere.

Question 3

Loxodromic spiral

Answer 3

If you were to depart from the geographic South Pole in a constant direction the route would cross all meridian at the same angle.

Question 4

Rhumb line

Answer 4

If you can get from point A to B on the same true direction then both points are on the same parallel of latitude.

Question 5

What side if the great circle on?

Answer 5

Pole side of the rhumb line track.

Question 6

What are northern and southern vertices?

Answer 6

Most northern and southern points on the Great circle track.

Question 7

Are vertices antipodal?

Answer 7

The vertices are ANTIPODAL in longitudinal terms and directly opposite in latitude terms:
Example: S55° W120° and N55° E060°. At either vertex the initial track direction is 090° or 270°.

Question 8

Great circle vertices

Answer 8

A Great Circle track crosses the equator at 2 points where the longitude is 90° removed from either the northern or southern vertices:
If you departed the southern vertex on an easterly track, you would cross the equator at W30°. Your longitude reduces from W120° to the equator crossing point at W030°. The longitude will continue to decrease until you reach the prime meridian - a change of longitude of 30° - and it then continues easterly until you reach E060°: a total of 90° change of longitude from the equator. If you departed the northern vertex on an easterly track, you would cross the equator at 150°E: E060° + 90° = E150°. The value of longitude has to increase as you travel further into the eastern hemisphere.

Question 9

Meridian of longitude

Answer 9

Semi-great circle and rhumb lines.
Becomes a great circle if joined with its anti meridian.

Question 10

Parallel of latitude

Answer 10

Small circles and rhumb lines

Question 11

Example question

Answer 11

Image in files wed 23 oct 16:51

Question 12

Rhumb lines

Answer 12

Have constant direction.
Cross every meridian at constant angle but is longer.

Question 13

Angles, increase/ decrease

Answer 13

Northern hemisphere west - decrease
N E - increase
S W - increase
S E - decrease

Question 14

A Great Circle has its southern vertex at S60° W060°. What is the track direction as you cross the Equator having departed in a north easterly direction from the southern vertex?

Answer 14

At equator N/S = 0 and E030, therefore directiin is 30. Then you can also do + 90 from equator to get E120 and then N60 as its opposite of southern hemisphere