latitude/longitude

[Dreamcast]

I came across a section on navigation out of "Flying the Big Jets" that I hope someone can explain to me.
In this chapter i read lines of LONGITUDE run from the Prime Meridian West to East. Each meridian is separated by 15 degrees of arc which is equivalent to 60mins or 4mins per degree.
However, lines of LATITUDE run from the Equator to the North Pole and EACH DEGREE is 60mins; therefore 15degrees of arc is equivalent to 15 hours and 90 degrees is 5400mins or 54 hours!!?? Is this correct?

[Dan Dare]

No

[Tallbloke]

I probably have this wrong as well, I thought 1 degree of latitude = 60 nautical miles.

[VTSP]

Dreamcast

I suspect you have taken some of this out of context. The first part of the statement is corret, in that it takes the Earth 1 hour to turn through 15 degrees.

But basic geometry will tell you that a degree is divided into 60 minutes and each minute is divided into 60 seconds (not minutes or seconds of time).

Tallbloke

You are right. The distance between 1 minute latitude (on the Earth's surface) is equal to 1 nautical mile.
(It doesn't work with the distance between minutes longitude though).


Mmmmm I think that's what I mean :)

[Oleo]

Hmmmmmm... I am probably going to embarrass myself here, but after spending all that time and dough on ATPL exams surely I can remember something! Here goes...

I think the first statement is correct, the earth turns through 360 degrees in 24 hours: 15 degrees an hour. We are talking about East-West here and it doesn't make much sense to talk about time running North-South.

At the equator, on a parallel of latitude (E/W), and on all the meridians of longitude (N/S) a degree = 60 minutes = 60 n.m. That is why we can only use the vertical scale on maps as a true measure of distance (oh, and this probably works on just certain map projections...). Don't get the minutes we talk about here confused with minutes of time, they are merely divisions (1/60th) of a degree.

So North-South, East-West there is always 60 minutes in degree, but this does not equate to time when running North-South (the Earth doesn't rotate that way!).

You have to use a formula (called the convergency formula if I remember correctly) to extract distance from a map; this varies with the latitude, because as we get nearer the poles the distance between meridians gets smaller until it finally reaches zero at the poles.

By the way, parallels of latitude also run from the Equator to the SOUTH pole... just thought an Australian might need to know that. :)

Anyway that's my measley tuppence worth. Hope I haven't lead you up the garden path. :)



[This message has been edited by Oleo (edited 15 June 2000).]