BoatBanter.com - View Single Post - One minute of Longitude--at your Latitude?

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wrote:

Bart Senior wrote:
How long is a minute of Longitude--at your Latitude?
And what is the formula to calcuate it?

There are 1440 minutes to a day, regardless of what latitude or
longitude you live in. Divide that by 360 (degrees) you get 4 (mins).
Every degree of longitude you have 4 mins.

Rgds
Ravi

Incorrect Ravi. Perhaps I should have been more clear. I am looking
for a distance not a time measurement.

One minute of arc is 1 nautical mile where ever you are. The earth is
not a sphere, there is about a 1% difference between the values at the
poles. Close enough for us to call in a sphere.

This works out nicely because for latitude, the spacing between
lines of latitude is constant. This was defined as a nautical mile
because it was fairly close the the distance used on land, the
statute mile. It is easier to use the nautical mile to avoid
constantly
converting from one unit to the other.

So one minute of latitude is one nautical mile and one can read
this measurement off the edge of a chart as well as the distance
scale on the bottom of the chart and be equally accurate.

For longitude lines which converge at the poles things are different.
At the poles a minute of longitude is impossibly short and approaches
zero as you approach the pole. Moving away from either of the poles
to the equator, one minute of arc approaches 1 [1 nautical mile].

There is a formula for this:

1 minute of longitude = the cosine of your latitude in nautical miles.

I live at 41.265 North The cosine of which is: .752.

So 1 minute of longitude at my location can be approximated
as 3/4 of a nautical mile. It is a handy thing for me to know.

BTW, thank for the invite. Do you have any pictures of your part of
the world, and your boats you can show us?

Bart