Ships must practice celestial navigation
28 points by HR01 a day ago | 20 comments
  • jas39 21 hours ago |
    A smartphone has all the sensors: tilt, clock, camera. Even compass, though hardly needed. This should be enough to build an app to determine position at sea.
    • bhhaskin 21 hours ago |
      Those likely aren't anywhere near accurate enough. And accuracy matters when being off by a few degrees can mean hundreds of miles.
      • UniverseHacker 21 hours ago |
        You’re right, but they can be used together with a sextant to instantly preform calculations that can be time consuming and difficult at sea.

        I use an app to double check my hand calculations.

        • bhhaskin 20 hours ago |
          At that point though you are using a sextant and a fancy calculator =P
    • saulpw 18 hours ago |
      But what happens when the smartphone is bricked by an EMP, or hacked by a nation-state virus? Haven't you ever seen Battlestar Galactica?
  • _xerces_ 21 hours ago |
    Curious how navigation at night was not possible without expensive equipment, sounds like they were relying only on starts in the morning and evening? Are the measuring something like angle of those morning/evening stars or their set/rise times with respect to the sun?
    • UniverseHacker 20 hours ago |
      It is not true- the authors sound very inexperienced with celestial navigation. There are many ways including the lunar distance method to get a position at night with regular equipment. The math is more complex than a simple noon solar sighting, but it can be done with just a regular cheap plastic sextant and a watch.

      It’s also no big deal to go 12 hours with no position. If you know your speed and heading you can accurately estimate your position much longer than that.

      Overall, they also made it sound almost impossibly difficult for a large team of professionals, when solo and otherwise short handed recreational sailors have been reliably sailing around the world with celestial navigation for more than a century- through all possible conditions.

      • danielvf 16 hours ago |
        Note that they were staying roughly 2 miles within the actual track, while having the bulk of the work being done by a combo of officers and newbs that they had just trained. That's high accuracy standards for celestial nav, not even counting that this is most of other people's first time doing this in anger.
    • quercusa 20 hours ago |
      And just how expensive is a bubble sextant?
      • wrycoder 13 hours ago |
        I have one I paid $150 for. But bubble sextants are usually only used on aircraft.
    • throw0101a 18 hours ago |
      > Curious how navigation at night was not possible without expensive equipment, sounds like they were relying only on starts in the morning and evening?

      As a sibling comment notes, it is possible. There are tables for lunar distance:

      * https://thenauticalalmanac.com/Lunar_Distance_Tables.html

      * https://en.wikipedia.org/wiki/Lunar_distance_(navigation)

      * https://www.starpath.com/resources2/brunner-lunars.pdf

      The planets Venus, Mars, Jupiter, and Saturn can be used, as well as several dozen planets (lookup tables in an almanac)

      * https://en.wikipedia.org/wiki/Nautical_almanac

      * https://thenauticalalmanac.com

      Two US military videos explaining the theory (ground points/GP, circle of position, etc):

      * USAF: https://www.youtube.com/watch?v=UV1V9-nnaAs

      * Army: https://www.youtube.com/watch?v=G4DRBi66cOA

      The USAF has a video because that's how planes used to do navigation outside of radio range—sextants on the ceiling of the cockpit:

      * https://www.youtube.com/watch?v=C7gAiI79nOY

      * https://www.youtube.com/watch?v=xc3rAlCDf54

  • throw0101a 18 hours ago |
    Training for this was discontinued, but brought back in 2016:

    * https://www.npr.org/2016/02/22/467210492/u-s-navy-brings-bac...

    Now if only the US (and others) would get their act together and build out a backup system to GNSS. China, for example, has built out an eLoran system:

    * https://rntfnd.org/2024/10/03/china-completes-national-elora...

    An old USAF video explaining how the theory works (it assumes a geocentric worldview: the Earth is the centre of the universe (but it's not flat :)):

    * https://www.youtube.com/watch?v=UV1V9-nnaAs

    • dzhiurgis 16 hours ago |
      > Now if only the US (and others) would get their act together and build out a backup system to GNSS

      They are moving towards quantum navigation (esp subs)

      • throw0101a 15 hours ago |
        > They are moving towards quantum navigation (esp subs)

        How does that help the merchant marine that is part of the logistical supply chain? Are container ships going to get this quantum nav boxes too? The US pays airlines a retainer to be a reserve fleet [1]: will they get these boxes as well in case of emergency?

        What happens to all the civilian infrastructure that need navigation and timing signals?

        Considering only the "military" ramifications of GNSS disruption is myopic.

        [1] https://en.wikipedia.org/wiki/Civil_Reserve_Air_Fleet

  • cafard 17 hours ago |
    > when celestial navigation is all but impossible without advanced, expensive equipment (i.e., a bubble sextant).

    Compared to what the Navy usually steers by, how advanced and expensive are bubble sextants?

  • arter4 8 hours ago |
    >As The American Practical Navigator (aka “Bowditch”) states, “No navigator should ever become completely dependent on electronic methods. The navigator who regularly navigates by blindly pushing buttons and reading the coordinates from ‘black boxes’ will not be prepared to use basic principles to improvise solutions in an emergency.”

    I wonder if this mindset is also applied, for example, to the rest of the military. Does the Army regularly practice land navigation? I know they get at least one landnav class, but it is a perishable skill. If you don't practice, you'll soon forget about it.

    I guess this could also be useful to civilians. Being able to do stuff without relying too much on electronics.

  • rickcarlino 16 minutes ago |
    Have there been any computer vision systems that can approximate celestial navigation using common sensors like a camera, An electronic compass, and a tilt sensor? Something like a computer vision based auto sextant. This is an idea I have thought about for a while but I have zero background in this area.