Why are the lines of latitude and longitude helpful to ship captains and pilots?

Question

thanks for your help.

and Why do you think degrees are used to determine latitude and longitude?

Answer 1

The lines of longitude (called meridians) show the north-south direction. On a map, we can tell the ship's or plane's heading (or course) by measuring the angle between the route and the line of longitude.

Lines of latitude tell us how far north (or south) we are. Latitude is relatively easy to determine (mariners and astronomers could do it over two thousand years ago).

The problem had always been longitude, which requires a very precise chronometer.

Long ago, a captain would sail (up or down) the coast until he reached the latitude of his destination, then sail across the ocean along that latitude until he saw the other coast (hopefully in sight of his destination). The ship would follow a line of latitude.


Degrees had to have two advantages: numbers easy to calculate (this is well before calculators) and numbers that represent some natural value.

The year is a little over 365 days. So the angle that the Sun would (apparently) cover among the stars in one day would make a nice standard for a "degree". Sure enough, some cultures (e.g., the Chinese) used an angle unit such that they needed 365.25 "degrees" to cover a complete circle (they had a different name, of course). It made for very difficult calculations, but they had created the concept of having pre-calculated tables over two thousand years ago.

We (so-called Western Civilization) inherited a unit such that a circle has 360 degrees. 360 is close to the number of days in a year (so we can say the Sun moves by "close to a degree" each day) and 360 is a number easily divisible by many other numbers (2, 3, 4, 5, 6, 8, 9, 10, 12, 15...)
This was very important before we had calculators or precalculated tables.

The Babylonians (before the Classical Greeks) then divided things in 60 parts. They used 60 for the same practical reason: easy to divide by 2, 3, 4, 5, 6, 10, 12, 15...

When European astronomers (much later) began writing in Latin, they called the first division of the degree and of the hour "pars minuta prima" (the first small part), and each of these parts was again divided into 60 smaller parts called "pars minuta secunda". From these expression, we have retained the words "minutes" (for the first division) and "seconds".

Some astronomers created even more levels, dividing by 60 at each level, up to 5 levels in one case. Today, we stop at seconds, and use decimal fractions of seconds if we want to go into smaller intervals.

When the Earth was thought to be spherical, it was easy to imagine angles measured at the centre, then represented as lines on the surface (actually, it was done first with the celestial sphere, then projected onto Earth, but the idea is the same).

It was easy to determine the location of the equator. A line going from the equator to the north pole (a meridian) would change it orientation (relative to Earth's centre) by 90 degrees. You can imagine the angle at the Earth's centre, made by a line from the North pole and a line from the equator: they make a 90 degree angle.

Keep going: after another 90 degrees, the line is back at the equator (but on the other side of the globe), another 90 and you are at the south pole and a fourth 90 degree trip to get back to the starting point. Total 360 degrees for a full circle (which is what we expected).

Take one of these degrees along the circle, and divide the length of its arc by 60: you get a minute of arc (also called an arc-minute -- this is to avoid confusion with the minute of time also used in astronomy and navigation).

The length of one minute of arc on Earth's surface became the British unit called "nautical mile".

In the 18th century, once the first crude calculators were invented, French scientists wanted to change the units of physics to decimal base (base 10). They created the metric system.

One part that never really caught on is the unit called a "grade" to measure angles and arcs. A full circle would have 400 grades, so that a right angle (e.g., latitudes from the equator to a pole) would have 100 grades.
Each grade would be divided into 100 centigrade.
The length of 1 centigrade on Earth's surface became the kilometre. (The metre is 1/1000 th of a kilometre).

But navigators were so used to degrees and nautical miles (and there were so many pre-calculated tables already in print with these units) that the grade was rarely used in navigation. That is why we still have the degrees.

Answer 2

Lines of Latitude and longitude are imaginary reference points that assist pilots and captains in navigation of the world's waterways and the airways. The combination of these lines forms a series of grids as seen in the link below. Hope this helps

Answer 3

They use lines of latitude and longitude in comparison with a map to find their nearest location. Although these days they rely primarily on GPS. Here's an article you may find helpful...

http://www.ncgia.ucsb.edu/education/curricula/giscc/units/u014/u014_f.html

Answer 4

just for your info
1 nautical mile = 1 min