Ships must practice celestial navigation
usni.org

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23 points

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HR01

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15 hours ago

15 comments

throw0101a ・ 9 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 ・ 6 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 ・ 5 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

_xerces_ ・ 11 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 ・ 11 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 ・ 7 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.

  • throw0101a ・ 8 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

  • quercusa ・ 10 hours ago

    And just how expensive is a bubble sextant?

    • wrycoder ・ 3 hours ago

      I have one I paid $150 for. But bubble sextants are usually only used on aircraft.

cafard ・ 8 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?

jas39 ・ 11 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 ・ 11 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 ・ 11 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 ・ 10 hours ago

        At that point though you are using a sextant and a fancy calculator =P

  • saulpw ・ 9 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?