Although a lot of tools have been digitized and consolidated into our smartphones, from cameras, music players, calendars, alarm clocks, flashlights, and of course phones, perhaps none are as useful as the GPS and navigational capabilities. The major weakness here, though, is that this is a single point of failure. If there’s no cell service, if the battery dies, or you find yourself flying a bomber during World War II then you’re going to need another way to navigate, possibly using something like this Astro Compass.
The compass, as its name implies, also doesn’t rely on using the Earth’s magnetic field since that would have been difficult or impossible inside of an airplane. Instead, it can use various celestial bodies to get a heading. But it’s not quite as simple as pointing it at a star and heading off into the wild blue yonder. First you’ll need to know the current time and date and look those up in a companion chart. The chart lists the global hour angle and the declination for a number of celestial bodies which can be put into the compass. From there the latitude is set and the local hour angle is calculated and set, and then the compass is rotated until the object is sighted. After all of that effort, a compass heading will be shown.
For all its complexity, a tool like this can be indispensable in situations where modern technology fails. While it does rely on precise tabulated astrometric data to be on hand, as long as that’s available it’s almost failsafe, especially compared to a modern smartphone. Of course, you’ll also need a fairly accurate way of timekeeping which can be difficult in some situations.
Its purpose is for navigation near the polar regions. Light aircraft and older heavies still use magnetic compasses every day. Properly compensated, they work fine. Until you get near the Arctic Circle. Then there are minor issues such as N being down and the longitude and latitude shifting over time.
Thanks for this. Every plane I’ve been in and flown has a compass, like a regular old magnetic one. That was even used to set the gyro heading indicator.
I knew bombers mostly used celestial navigation and dead reckoning and it makes sense that a lot of those routes would be over or near the pole. From reading up even “normal” celestial navigation gets weird near the poles.
Not just for the polar regions, it’s for determining location worldwide. Despite the name of ‘astro compass’, it’s not for determining just the compass bearing. If you know the time of day and the apparent position of a star, then you can calculate both your longitude & latitude.
I have one an old one of these, from an Astro Lancaster used by the RAAF. Australians in WWII did not need to navigate near the poles :-)
Also, fun fact, it’s highly radioactive! They daubed it liberally in radium paint so it could be used in pitch black even if the cabin lights failed.
Actually I take that back a bit. It’s been ages since I read the manual. Turns out it seems to be primarily used for finding your true heading, and doesn’t mention finding your lat/long after all.
But again, super useful worldwide.
Thanks for pointing out that it is an aircraft sextant. It was the only way to navigate oceanic routes until LORAN & GPS. I was offered one by a friend who had been Chief Pilot SW Pacific air transport under McArthur and circumnavigated in a 37’ ketch after retiring from flying for the airlines. I turned it down for the simple reason I was in grad school and really could not cope with more stuff. We discussed my decision at some length as he was disappointed that I turned it down. I hoped to go cruising, but it never happened.
They are definitely in the uber cool category though not quite in the league with my recently acquired Kern DKM1 autocollimating 5 second theodolite. Now I’d love to have it. But my situation 45 years ago was a bit different. A plastic Davis marine sextant would do for learning celestial navigation and they were cheap the moment I had reason to buy an ephemeris. Which were NOT cheap and had to constantly be replaced.
The bubble levels provide the required artificial horizon for the star shots and everything else is just like a boat. You need time, tables and multiple observations to determine your location. That’s why large planes carried a navigator who typically also served as the bombardier. Before Chain Home this was all the lead navigator for a night run had. And even with radio assistance, the navigator would always be checking as German interference with Chain Home would have resulted in loss of the plane and crew.
Fairly quickly after the war LORAN took over the heavy lifting for position and compass compensation became the dominant use case. So you were entirely correct. Same instrument, but newer and different manual. The primary use case merely changed. I’ve got about 100 hours of “ball and compass” time which is why I had to cry foul.
Very nifty! And I feel your pain at having to turn it down.
I did actually buy one of those Davis sextants a few years ago, but never got around to using it in anger.
After playing with both the astro compass and the sextant, I have a ton of respect for anyone that had to sit in the navigator’s seat at 3am and be responsible for everyone’s being able to find home safe. Calculations that seem easy & trivial when sitting at home in a comfy chair suddenly become rather important to do right.
Is the Horror Fraught sextant actually useful?
I know they have a disclaimer on the box that it it shouldn’t be used for navigation, or that it was meant only to be a decoration, but it looks the part.
As you mention Chain Home; I’m currently reading “Most Secret War” by R. V. Jones. A very interesting person and the science work done to protect Great Britain, its citizens, and military during WWII.
https://www.goodreads.com/book/show/1127842.Most_Secret_War
I started with a davis plastic sextant and it was such hot garbage I almost quit entirely. Never held calibration to remotely be repeatable or usable and the solar filter design was terrible. Go to flip up one filter and the stack of them goes up instead and you are looking through a telescope at the sun. Not that the telescope is even remotely good- plastic kids binoculars from the zoo are about as good. No thanks. Fortunately I worked an extra shift, bought an eBay special older Astra iiib and boy what a delight proper instruments are. Truly a joy to use. Very glad I stuck with it.
“If there’s no cell service, if the battery dies, or you find yourself flying a bomber during World War II then you’re going to need another way to navigate, possibly using something like this Astro Compass.”
Why, were the British isles so difficult to find? Asking for a friend..
Well the British Isles couldn’t have been that difficult to find. I mean “Wrong Way” Corrigan found them.
Night bombing, cloud cover, fog of war…
“Your” side had their share of troubles navigating aircraft back then too!
Read the book I mentioned above, it explains a LOT!
I recall a proposal from when the Pinephone was new for a non-GPS navigation app. Using the clock, gyros, and camera it should be reasonably easy to track at least the sun and moon and reduce that to a CEP of probably a few hundred meters if elevation can be established. Not good enough for turn-by-turn but good enough to help a right seat navigator if they can see street signs. Probably pretty great for nav in a boat, Cessna, or wilderness hike.
I understand that there is no working GPS in the middle east right now to deprive Iran one route of accurate tracking after their last few long range ballistic missile salvos.
I recall a proposal from when the Pinephone was new for a non-GPS navigation app. Using the clock, gyros, and camera it should be reasonably easy to track at least the sun and moon and reduce that to a CEP of probably a few hundred meters if elevation can be established. Not good enough for turn-by-turn but good enough to help a right seat navigator if they can see street signs. Probably pretty great for nav in a boat, Cessna, or wilderness hike.
I understand that there is no working GPS in the middle east right now to deprive Iran one route of accurate tracking after their last few long range ballistic missile salvos.
Celestial navigation involves taking angular measurements at precise times. Each measurement provides a single piece of information, that you are somewhere on a circle of a certain diameter with a center at a particular latitude and longitude. A noon shot will give latitude only unless you have absolute time and an ephemeris. You can interpolate noon by taking multiple shots before and after noon using only relative time. But with accurate time, a pair of shots separated by a few hours will put you on a pair of circles which intersect at 2 places. One is your current position and the other is very far away.
A running fix is a bit more involved as you have to adjust for course and speed between shots. I never actually learned all the details, but studied the problem until I understood the mathematics properly.
Celestial navigation would be very effective with an ephemeris program and camera pointed at the sky as a jam proof drone guidance system, though with weather limitations.
a good example of why flight crew size has shrunk over time.
Back in the day prior to GNSS, Land surveyors used instruments that would measure horizontal and vertical angles such as Theodolites and Transits to find unknowns. If any two of latitude, longitude, time or azimuth were known, any two unknowns could be found using the techniques of field astronomy.
GPS on a phone does NOT require cell service to work. You can get self contained GPS units with no phone or other internet connection, these were the standard before GPS was integrated into phones.
Where navigation on a mobile phone may require an internet service, is to display maps, however, Google Maps (and presumably other maps apps) can also cache maps on the phone. So provided you have some idea where you are intending to go, you just need to ensure that you download the maps covering the expected region, plus an extended region if you expect to deviate from your planned route! Plain paper maps will also work just as well, if less conveniently if you know how to use them and remembered to pack them!
Not quite true. Almanac and Ephemeris (especially very accurate) data can be downloaded from the internet, as well as approximate position and time from the cell tower. These may or may not be required, depending on how long you want to wait. The Satellites transmit the data frames really slowly ( 300 bps ? 50 ?)
Back in the day, there were chip sets that offloaded all the work, so they needed communications, even post processing.
-Gar.