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Using a Sextant

sextant is an instrument generally used to measure the altitude of a celestial object above the horizon. Making this measurement is known as sighting the object, shooting the object, or taking a sight. The angle, and the time when it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at noon to find one’s latitude. Held horizontally, the sextant can be used to measure the angle between any two objects, such as between two lighthouses, which will, similarly, allow for calculation of a line of position on a chart.

Celestial navigation continues to be used by private yachtsmen, and particularly by long-distance cruising yachts around the world. For small cruising boat crews, celestial navigation is generally considered an essential skill when venturing beyond visual range of land. Although GPS (Global Positioning System) technology is reliable, offshore yachtsmen use celestial navigation as either a primary navigational tool or as a backup.

using sextant

Wikipedia contributors, “Sextant,” Wikipedia, The Free Encyclopedia,

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This Post Has 4 Comments

  1. This is a very interesting device and it’s too bad more people have no idea what it is used for. Lots of people don’t realize that a mathematical analysis can be made of this instrument that can explain its
    usefulness. Unfortunately, this is not a new phenomenon but it appears to me that not much progress is being made to improve this. Recently, I came across an article that stated the United States is slipping in our reasoning ability. I feel that high school students need far more hands on exposure to devices such as this than they are now getting. I taught high school physics for eight years and I speak from experience. Thanks for this opportunity.

  2. When I was repairing some oceanographic instrumentation at the Naval Gun Factory yard in DC some time ago I set my instruments up on a large crate of sextants that were obviously no longer used for navigation. They were such a curiosity to me that only recently came to mind while reading “Longitude” by Dava Sobel. Now that I have a layman’s understanding of what it took to navigate in those times I am amazed that they were able to arrive at a destination at all given the information gleaned from sightings and the associated error.

    Having said that what an amazing education one can get about navigation of early times using the universe that surrounds us as our tiny planet hurtles through space. Possibly more amazing was man’s reasoning/ability using primitive tools to develop a sea stable chronometer and collect/record the heavens above for all seasons so that they could indeed sail the seas!

    1. I don’t respond to people much, but you said a lot there Joseph! Young people would definitely benefit from being exposed to and challenged by an instrument like the sextant. I’m learning about celestial navigation to give my mind something to chew on during a tough year of life! I live on the coast of NC and am no stranger to the sector of ocean that is beyond our continental shelf. But I have deep emotional ties to the ocean, like a lot of us, and the navigators of yore have always been my heros. Anyway, I do believe that high schools would see mental health improvements and could even prevent school shootings. Well said Joseph!

  3. It’s amazing the usefulness of a sextant. I’ve always dreamed of sailing but never had the chance too. But consequently because of my interest in navigation I taught myself from books how to use the sextant. One of the things I use to use the sextant for believe it or not was in my job of broadcasting engineering. I use to work with FM and TV broadcast towers, and the owner of the towers wanted a survey of all other customers on the tower which would lease tower space for two-way radio repeaters and microwave repeater hops. Since they charged their customers by height and space needed, the broadcasting facility owner would need an inventory of antennas and their respective heights on the tower. The sextant is not the ideal instrument, but certainly was portable enough to walk out into the field and get angle and distance from tower and easily calculate the height of each antenna on the broadcasting tower for the owner to a very close accuracy. So even though I never navigated and sailed, the sextant was a very useful instrument. I think anyone who enjoys mathematics and wants to impress upon the younger generation the importance of understanding math, to find such instruments like the sextant fascinating and useful.

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