Before Satellite navigation how did boats and ships find their way ?

I was wondering back ion the old days when there was no satellite up in space how did travellers with boats and ships find their way to their destination ?








how ?





thnx|||Celestial navigation is any of several techniques for finding your way in the broad ocean. Celestial navigators use compass, sextants, clocks, charts, spherical trigonometry, and vector algebra to locate their ship.





The basic technique is to measure the altitude of three (or more) stars and record the time of the measurement. The measurement from the first star produces a circle on the surface of Earth whose diameter is a secant line inside the geosphere. The ship is somewhere on that circle. The second star also produces a circle, which intersects the first circle in two points. The third star produces a circle that tells the navigator which of those points represents the current position of the ship.





There are details, of course. The altitude of the star must be corrected for the height of the navigator's eye above the water while he is using the sextant. It must also be corrected for atmospheric refraction. And if the object is a planet, instead of a star, it must also be corrected for parallax.





Another technique is called "dead reckoning," which is partly an extrapolation of the ship's progress from the previous 24 hours into the next 24 hours, with modifications intended to allow for changes in the wind and in the ocean currents.





Another technique is triangulation from observable landmarks. If the ship is passing an island which has been explored and mapped, then features of the island's terrain can be used to estimate the ship's position, course, and speed. This technique is also known as (nautical) piloting, but it can assist in navigation also.|||Latitude is quite easy to determine at sea. You simply measure the altitude of the Sun at noon. Noon is when the Sun is at it's highest, so you just measure it's altitude repeatedly for 5 minutes either sie of when you expect noon. The highest measured altitude was the noon altitude. From that you can calculate latitude. Sailors would sail to a specific latitude and then follow that line of latitude all the way across the ocean until the could see the coast on the other side.





Longitude is harder to measure and huge efforts were made to find a way to measure if accurately. The only way (it was established) is to have an accurate clock (a chronometer) on board. Since the Earth is a sphere of 360 degrees all round, every hour of time difference represents 15 degrees. By using the chronometer to keep the time of your departure location and using your noon sights to determine local time you can work out your longitude.





That's how they did it, and often how we still do it!|||With compasses and Sextants it became easy to find Latitude. In the northern hemisphere if you can find Polaris, you can estimate its elevation over the northern horizon, this angle would equal your latitude. Longitude required knowing your time and the time at Greenwich England. If it is noon in Greenwich and 6 AM where you are, you are 6 x 15 degrees west of Greenwich or 90 degrees West longitude. This required a chronometer or an astronomical method. Hence the formation of the US Naval Observatory to determine the precise time for astronomical events like the orbits of Jupiter's Galilean moons. See the book "Longitude" by Dava Sobel.|||They used a chronometer (a very accurate clock), a sextant (a device for measuring the angle between the Sun or other stars and the horizon), and a reference book called the Nautical Almanac. The technique is known as "celestial navigation" and is extremely accurate.|||One of these:





http://www.definaauctions.com/Ships%20co鈥?/a>





http://www.infovisual.info/05/076_en.htm鈥?/a>|||a whole bunch of new instruments.


you can probably find some in a world history textbook.


i don't remember the names.|||several things were used it is as to what time period your referring to.the starts were used first as was the sun then the sundial and compass|||Star charts were piloted so ships could circumnavigate the globe.


A sextant was the instrument used.|||Radio waves and radar.





Chronometers, compasses, sextants, astrolabes|||Compasses.


Sextants.


The stars.