Great Circle routes

[wonkywinch]

Rather than wander off track on another thread (the old oil one), questions were raised about why planes don't fly in straight lines around the world and I explained that over a sphere, a great circle route is a straight line.

As an example, here is the route from Heathrow (EGLL) to Seattle (KSEA) I did a couple of years back. Heathrow is at about 51.5 degrees north and Seattle 47 degrees north, so it is south of London (it's on the same latitude as Nantes, France). Passengers watching the moving map would see us tracking north over Scotland, Iceland and Greenland to get there. Here is the flight planning chart which explains all. Our track is the line with triangles on it.

 

[Stemar]

Thanks for that. Are the other lines frontal systems with wind speeds?

 

[GHA]

opencpn does it automatically.

 

[AntarcticPilot]

We had a beautiful view of the Canadian Arctic Archipelago on a flight to Vancouver once.

Simplest way to explain great circles is to get sceptics to stretch a string between two points on a globe.

 

[wonkywinch]

Thanks for that. Are the other lines frontal systems with wind speeds?

They are jet streams with wind speeds and altitude of the core. The solid triangle marks on the jet are each 50kts, the long lines 10kts and the short ones 5kts so the jet over the north of Ireland is 95kts at 28,000 feet.

 

[wonkywinch]

We had a beautiful view of the Canadian Arctic Archipelago on a flight to Vancouver once.

Simplest way to explain great circles is to get sceptics to stretch a string between two points on a globe.

How would you deal with a flat earther?

 

[AntarcticPilot]

How would you deal with a flat earther?

Flat Earthers are too irrational for it to be worth trying. Eratosthenes' experiment provided ample evidence of the spherical nature of the earth; everything since then, up to and including eye witness accounts, simply confirms what he first demonstrated.

 

[Minerva]

How would you deal with a flat earther?

Chuck them out the aeroplane door mid flight for a closer inspection of the great circle?

 

[Roberto]

Chuck them out the aeroplane door mid flight for a closer inspection of the great circle?

A-ha, so onboard last Boeing 737 flight they were flatearthers wanting to inspect

 

[fredrussell]

Do any flat-earthers really think the earth is flat? I’ve always assumed they just like the attention and enjoy a good argument.

 

[Minerva]

Do any flat-earthers really think the earth is flat? I’ve always assumed they just like the attention and enjoy a good argument.

There are folk out there that genuinely think bill gates put 5g microchips into a vaccine so that he could track their whereabouts!

Never underestimate the levels of stupidity in some parts of the general public.

 

[LittleSister]

I blame Gerardus Mercator!

 

[Daydream believer]

It is all complicated by the flight of the aeroplane. That flies high up in the air & down again in a curve. That flight line distorts the flatness of the earth, so people think that the earth is round. Difficult to explain, but you can see it when you look out the window of the plane.

 

[Buck Turgidson]

It doesn't get much flatter than the great Canadian FA. Most boring terrain in the world.

 

[crewman]

On YouTube there is a claim that there is a Great Circle route from England to New Zealand via the Drake Passage. Anyone know if it is true?

 

[Roberto]

I have the impression Great Circle routes are a notion spilled from plane/merchant maritime world which is most often useless for a sailboat: it there any one ocean route where one might want to follow a GC route instead of a weather route? Where the increase in distance by not following a GC route is not more than offset by the advantage of better wind direction/speed? Even in very high latitudes, say Japan to Alaska, or the northern option in the Ostar, the GC route will always be subordinate to the existence of correct weather. In temperate latitudes, the big high pressure systems in the middle of the oceans will make half of the crossings deviate a lot from GC.
Carib to Azores for example, the difference between GC and loxodromy is a few tens of miles over 2000+, a weather route will usually be near that; whereas no one in his right mind would try and follow the GC going Canaries to Caribbean.
The Southern hemisphere has a lot less land so maybe sailboats GC routes make more sense there?

 

[penberth3]

There are folk out there that genuinely think bill gates put 5g microchips into a vaccine so that he could track their whereabouts!

Never underestimate the levels of stupidity in some parts of the general public.

Corrected for you.

 

[KevO]

Ah, the GCFA. Haven't heard that for a while

 

[GHA]

There are folk out there that genuinely think bill gates put 5g microchips into a vaccine so that he could track their whereabouts!

Never underestimate the levels of stupidity in some parts of the general public.

...and they walk among us.....

 

[Alan S]

It is all complicated by the flight of the aeroplane. That flies high up in the air & down again in a curve. That flight line distorts the flatness of the earth, so people think that the earth is round. Difficult to explain, but you can see it when you look out the window of the plane.

Hard to believe that on a sailing forum there would be people who don't understand Great Circles, never mind believe that the Earth is flat.
I despair.