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.
“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..