Departure, Earth convergence (24-05-18) Flashcards Preview

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Flashcards in Departure, Earth convergence (24-05-18) Deck (11)
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1

What is departure or rhumb line distance?

The distance between 2 positions where the track crosses all meridians at the same angle (on a small circle)

2

What is the equation for departure?

Departure = (Chlong x 60) x cos(mean(lat))

Distance covered as if at the equator but scaled down due to latitude.

3

What is the distance along a latitude called?

Departure/rhumb line distance

4

What is the max distance between 2 positions that short distance approximation can be used?

400nm 

5

How do you use short distance approximation?

Make a triangle using minutes of arc from longitude change and departure with mean latitude.

Use pythagoras for the actual distance

Use trig for the bearing.

6

What is Earth convergency?

the angle between 2 meridians, at a particular latitude, altering the angle between great circle tracks and meridians.

7

What is the equation for earth convergency?

EC = Chlong x sin(mean(lat))

8

What is the technique for working out a great circle track at one meridian from another?

Transpose a ‘ghost’ version of the starting meridian onto the second and work out EC.

the transposed ghost meridian will tell you whether to add or subtract EC.

9

What is conversion angle?

The angle between a rhumb line and a great circle between 2 points (measured at departure and arrival points).

10

What is the equation for Conversion angle?

CA = 1/2Chlong x sin(mean(lat)) = 1/2 EC

11

What is the difference between great circle and rhumb line tracks at the half way point between 2 positions?

It is the same, there is not difference