Use of Celestial Navigation Today

No, we can’t yet as it still is a requirement of the Solas (1997) Regulations, which states that all ships of over 150 tons gross tonnage, when engaged on International voyages, shall have onboard an efficient daylight signalling lamp which shall not be solely dependent upon the ship’s main source of electrical power.

If the GPS system fails and Loran is already no longer available the sextant is the only instrument left to get a position fix. But are mariners these days knowledgeable enough to make the necessary calculations? You have to train this technique but I doubt that this is done on a regular basis at the moment.

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I concur. Flashing light is an old technology probably best left dead and buried … just like the sextant? :slightly_smiling_face:




An ingenious solution is the CamSextant Iphone Sextant which makes use of the iPhone’s gyro sensor. There is a CamSextant app available.

Everybody had there own preferences for the calculations. On Dutch ship the Lieuwen’s Record Tables were often used. He was a nautical school teacher. Some used the Sight Reduction Tables HO249. Very popular also were the Ageton Tables which used to be in the Bowditch Almanac but not anymore. Not even an EMP can destroy a sextant, mechanical (!) clock and the 32 pages of the Ageton Tables. The hard part today is the regular training. The accuracy of the position fix depends entirely on the accuracy of the sextant measurements. Finding a good horizon is often the trickiest part and that must be trained. You also have to know your personal error, which most people have, which must be added or subtracted to the measurements.

The quickest method these days is I suppose to use the Starpilot program installed on one of those nifty scientific calculators.

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The scary part is if the sextant provides a different answer from what the person expects what are they going to believe. Both of us had completed years of sea time with nothing but else but a sextant ,echo sounder, a DF receiver that had been cleverly designed to receive no radio station that any young officer might like to listen to , and a dodgy radar.
At least I had it better than some of my buddies in another company where there was no radar or gyro compass and apart from the DF and echo sounder the only other electrical equipment on the bridge was the electric navigation light panel.


Is it really that hard to stay proficient in celnav? A gyro check by azimuth or amplitude will keep you up to snuff on the almanac and (in the case of an azimuth) Pub 229 or another method of solving the triangle. If you can get through an azimuth, the plug and chug of a reduction isn’t the hard part; proficiency in physically handling the sextant becomes the challenge.

All the more reason to break it out (weekly?) and keep the muscle memory intact. While celnav isn’t needed at my current job, I do bring my sextant to work in the summer and, when geography allows, try for sunlines and LAN or evening stars. If we are professionals, I see no reason to let that skill die. Shit happens and it is better to be prepared than caught flat footed.


From the project page:

Warnings before you start

  1. While the phone gyro is a nice piece of equipment, it is not nearly as precise as a marine sextant. In a rocking boat, the gyro response is even worse. So - if you want to practice celestial navigation - get yourself a marine sextant .
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you cant hack the celestrial navigation system

How about a high tech camera to follow the sky connected to computer, runs non stop, sun, moon, stars etc with gyro accelarometers etc for when it needs to DR?
Could give you DR worst case and could be accurate at other times.

I didnot consider this as a serious option, should have mentioned this.

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That was already years ago realized by this biscuit tin that contains a Nortronic Inertial Navigation System (INS) and Astro Navigation System (ANS) type NAS-14V2 that was on board the SR-71 Blackbird fighter jet that could fly at a speed of Mach 3.2. The entire project has since been declassified and some information is gradually becoming known. The INS is updated by the ANS. No vulnerable GPS is required for this. In any case, the constellations in the sky cannot be manipulated! It makes sense to have a navigation system that relies on something that cannot be hacked or spoofed - the stars.

This system was able to follow 58, later expanded to 61, stars even during the day even when it was still on the runway. I read somewhere that 4 - 8 of those navigable stars, depending on the sky position and the position of the aircraft, were followed. It has is a ‘blue light’ source star tracker, but it is not clear what this means, probably to track stars under daylight conditions.

While older CNS (Celestial Navigation System) had telescopes mounted on gimbals reading only 64 stars, a modern device could have an array of sensors tracking thousands of stars instead of 64. A device like this could place a fast-moving fighter within a 300 foot square in time and space.

Northrop Grumman placed one of the new generation CNS or Astro Trackers in their RC-135 surveillance plane called the “LN-120G Stellar-Inertial-GPS navigation system”. It is a combination of GPS and astro tracking embedded within an inertial navigation system (INS), giving it a triple redundancy.


Does it still have to be connected to a power source as well as the screen to get your position? If so, then a lightning strike could still knock out your GPS and the tracker unit? Could solar flares affect it with electromagnetic interference?

Just curious to know if it would be better to have a sextant which doesn’t rely on a power source/ still works if your vessel goes into partial blackout.


For a sextant to be of use one has to use it. It is an “art” as well as “science” No matter how you reduce that sight to a line of position the accuracy of the actual sun or star shot is of equal or more importance. An example is catching a distant wave top instead of the true horizon. The smaller the platform the more difficult the task. The beauty of the modern bridge is that ln learning the art part one has the advantage of knowing the current exact position. Before electronic navigation, we only knew where we had been. Even a round of morning or evening stars is old by the time it is worked out and plotted.
Here is a short manual from WW2 that may be all that is needed. Scroll down to the Navigation section if you don’t want to read it all.

If one wants to hone their skills for under $30.00:
My gear from 1981. Professionally I worked Tugs. For fun, I sailed Oceans on my 32 ft Ketch.


Call me old fashioned but what’s wrong with dead reckoning? Sure there are some small islands in the middle of nowhere but most ports are on continents. Continents are big.


Depending on how well you judge the set, you can end up pretty far from where you think you are in the span of an ocean. You need to see the island you’re aiming for or correctly identify a coastal feature, and countless ships have been lost because DR wasn’t precise enough. Granted, that sort of thing is more likely to happen when you drift around the doldrums for a few weeks, but I think it’s still a relevant consideration.

It’s been a long time since I actually checked my DR precision, and I very rarely plot estimated positions for any kind of serious distance, but my intuition tells me that I’m usually a couple of degrees off. How close do you manage to get?

Well, I can hit a gnats ass at 5000 miles but this isn’t about me, it’s about capt joe schmoe.

In any case I was referring to the scenario where a deep-sea ship lost GPS. Worse case scenario would be Singapore Straits where ships are four wide in the narrow lanes.

In mid-ocean adjust the track so that land-fall can be made somewhere free of dangers.

Also getting up to speed on celestial isn’t that hard. Cadets go from zero to adequate in three days.


One day west out of the Canary Islands we came across a small bulker eastbound. Every time we tried to open our CPA he would turn to close it again. When we finally got visual, they were down on the bow with a port list. When we got within a mile they contacted us on what seemed to be a walkie talkie. Is this the right way to the Canary Islands? I am not sure what his problems were but it sure ended the argument that in this day and age why do you need Celestial navigation

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Within easy radar range of shore, with VTS on the horn? My worst case scenario would be something like fire in heavy weather, causing propulsion loss for a couple of days and permanent electrical power loss. When you’re back up and running, you have only a vague idea of where you are, a magnetic heading reference, and insufficient fuel to overshoot St. Helena by more than a day or two.

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Well, yes, I should have said likely scenario. Of course it’s possible to imagine a scenario where a position was needed but no time to come up to speed. But standard risk analysis doesn’t work that way.

With regards to Singapore, not much room for error. if there was a sudden, unexpected system loss there is a high probability most ship’s officers are going to have difficulty shifting to terrestrial methods mid-stride. Be much less risk if the ship was mid-ocean.

Well, I’m a scenario construer :stuck_out_tongue:

I’ve had to switch to radar positioning mid-stride, in tight quarters and very low visibility, which was indeed much more stressful than having to plot a couple of estimated positions in open waters. Still, your scenario is one in which neither celestial navigation nor ded reckoning is the go-to tool.

Sustained loss of satellite positioning is one of those high consequence, low probability events that is tricky to analyze. However, I’d expect any risk / benefit analysis to conclude that you should carry a sextant and maintain currency, since the cost is very small compared to the potential consequence.


To do be able to do a sophisticated DR calculation it is obvious that a ship’s position is affected by influences besides its own course and speed, such as leeway and current. Especially container ships are getting larger and larger and the windage area for instance for ULCS’s is even between 13000 and 18000 square meters.

The drift angles due to wind force and speed are shown in the table. If it is the intention to reach a certain waypoint the course must be corrected for the relevant drift and current. For the dead reckoning the availability of a Doppler log is certainly benificial for the accuracy of the calculation. As far as the current is concerned, a lot of information is available and must be included in the DR.

In most cases it is not required to hit a waypoint. Consider Yokohama to U.S. West Coast for example The Aleutian Island chain is 1100 miles long. Plus they are volcanic, high and steep to. Put the radar on 48 mile scale they are going to be hard to miss.

Not to mention almost always overcast.