What did Sailors use to calculate their location based on the position of the sun and stars in relation to the horizon?

Answer 1

The angle of the North Star ('Polaris', the 'Pole Star') above the horizon is very nearly
equal to your latitude on the earth, north of the equator.

It could be off by 35 miles either way, but that's about as close as it can be measured
from a bobbing boat anyway, and as close as you need to know when you're out in the
middle of an ocean.

Note that this doesn't work in the Southern Hemisphere. If you're south of the equator,
then the North Star is below your horizon. (Your "north latitude" is negative, and so is the
elevation of the North Star.)

Answer 2

Nowadays he would use a GPS unit. However, in the past he would observe the angle to the horizon of the mid day sun. This measurement would enable him to work out his latitude north or south of the equator.

Answer 3

Early navigators ... at least in the northern Hemisphere ... were able to determine their latitude by

measuring the angle between the horizon and the North Star (Polaris). That angle is always within

less than 1/2 degree of the observer's north latitude.

The north Star is never visible to observers south of the equator, and there is no similarly bright star

anywhere near the south celestial pole. So navigators in the southern Hemisphere always had to be

somewhat more clever.

Answer 4

-- by measuring the altitude of Polaris above the northern horizon at any time

during a clear night

-- by measuring the altitude above the horizon of any one of up to 100 other

convenient stars, all catalogued in the sailor's nautical almanac, at the time

when the star crossed due south on any clear night.

Quite a trick when the ship is rolling, yawing, and pitching. And completely impossible

when you've been at sea in fog and overcast for a week. But that was the only method

that existed, until less than 100 years ago. And they did it, and sailed across oceans

and around the world that way.

Answer 5

It used to be the 'sextant', an optical instrument with which the altitude of a selected

star in the sky, usually the North Star, could be measured.

Nowadays, a hand-held GPS receiver that runs on a pair of AA cells costs less than

a good sextant, and produces a result faster, easier, and with greater accuracy.

Answer 6

by using the astolabe