When I first learned about good circles, I discovered them come be among the many eye-opening, head-scratching and strangely beautiful ideas in navigation.

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I had not come throughout them in ~ all before my tool Rating aviation training and there is a great reason for this – this is the minute when navigation planning go big.*


A an excellent Circle – some simple definitions:

The line that divides a sphere in two.


Any circle that passes through two clues that space opposite each various other on a sphere.

The biggest circle that will certainly fit about snuggly a sphere.Imagine a chop hoop the a beachball can only simply fit perfect through.

Great circles room longest one you can attract on a sphere.

The planet is not a perfect sphere, yet we deserve to think that it together one. The Equator is a great circle, however the Tropics the Cancer and also Capricorn room not (they are smaller sized than the Equator). And the Arctic and Antarctic one are also smaller 보다 the Tropics and also definitely not an excellent circles.

On the left globe, all the present running optimal to bottom (longitude) are an excellent circles. Yet the Equator is the only one of the horizontal lines (latitude) one that is.

The meridians – or currently of longitude – are also perfect circles. The Greenwich Meridian goes through Greenwich and additionally the North and also South Poles and any line that goes with both the North and South Poles have to be a great circle, due to the fact that the Poles room opposite every other.

(Remember: any type of circle the passes v two points opposite each various other on a ball is a good circle.)

Why are good circles important in navigation? due to the fact that they display us the shortest routes between two points on a sphere. If we desire to travel the shortest distance throughout any sphere, earth being the obvious choice for most of us, girlfriend actually need to head in the direction of the allude on the opposite next of that sphere.

So far, reasonably logical and intuitive maybe. However things get a small bit much more interesting once we lug cardinal directions and also the compass into it. Why?

Because an excellent circles mean you regularly have come head north to arrive somewhere a small south of you. And also vice versa.Now perhaps you have the right to see why I found this ide a head-scratcher in ~ first. However bear v it, it defines a lot of what you’ll see in long distance journeys. Let’s look at a actual example.

The various other day i was top top an waiting Canada trip from Calgary, Alberta to London. These cities space on roughly the exact same latitude, roughly 51 N. So surely to fly from Calgary come London, i m sorry is practically exactly early east, we should fly early east?

Well us could, however it would certainly be a much much longer journey 보다 if we discovered the great circle route and also took that. And also to do that we should fly phibìc of east for the very first part of the journey, then east, then south of east. Due to the fact that this is the straight line way to carry out it and it will shave hrs off the journey.

Below space the photos i took that the ago of the seat route map on wait Canada.

The an excellent circle monitor from Calgary to London
Heading away from Calgary, note the compass heading: Northeast.
Arriving right into the UK, an alert the compass heading: southern of east.
Approaching London, heading well southern of east.

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Time to check out if you’ve obtained this nailed. Imagine you must start a trip from London to Nagasaki, Japan and also want to monitor the shortest route. Japan is the course fine to the east of London. That is also much more than a thousands miles south of London. Have a guess: v of the heading you’d set off in to monitor a good circle, then see exactly how you did by reading the answer in this post: London to Nagasaki by an excellent Circle.

**(There are two varieties of flying – the kind when you can see stuff and the kind when you can’t.The tool Rating (‘IR’) is among the greatest stepping stones in aviation, that is the ticket the qualifies a pilot to fly in what pilots call Instrument Meteorological problems (‘IMC’) – and also what typical folk contact CLOUDS.

To obtain this rating you need to pass much an ext serious exams 보다 are necessary to gain a basic pilot’s licence. They encompass the kind of navigation and also route planning crucial to fly a big jet thousands of miles. And also this is where great Circles come in.)