Lots of critical military devices still use star based navigation, and likely even more will in the future, since it's become obvious we can't rely on NAVSTAR GPS to be working if we go to war.

ICBM's inclusive. I've always thought it poetic that if humanity destroys itself, one of its final acts of comprehension will be that of a robot contemplating the heavens. We end as we began.

I pine for a commercial/hobbyist grade celestial navigation system (point CCD at sky, get position). If anyone has any recommendations or pointers, would love them.

Would this potentially work during the day, or do you need to be able to see stars? If you can see the Sun I guess that should be good enough, if the sensor can even handle that without clipping to hell?

Do you also have to be able to accurately measure angle to the horizon too? I'm not all that familiar with celestial navigation in practice.

You don't measure angle to the horizon, but angle from gravitational/geodetic "up", so you'd need probably a good leveling mechanism plus an inertial device, (if you want to be moving). And a reference to correct geodetic up to elliptical up (similar to a magnetic declination, but for gravity).

But even military quality geodetic transits can only get your longitude +/-100yds, plus they weigh a few hundred pounds, need to be manually set up, leveled, and a person has to do the actual observation (click a button as a star passes through the crosshair).

Granted this is decades old technology, (and I think actually used a electronic-mechanical computer) but I don't know that much has changed since then, at least in the unclassified world.

I believe ships at sea doing it manually with a sextant or similar device are only going for accuracy in the magnitude of 1-10 nautical miles.

So depending on what you're trying to do, it's questionable how much this might help you.

To me, there's something profound about the idea of locating yourself in 3D space using light from stars light years away. GPS is great, but the universe is inherently providing beacons (not just stars, but also pulsars [2]) for positioning and guidance. That's very cool!

[1] https://timeandnavigation.si.edu/multimedia-asset/nortronics... (Nortronics NAS-14V2 Astroinertial Navigation System: Mounted behind the SR-71’s cockpit, this unit, affectionately known as “R2-D2,” computed navigational fixes using stars sighted through the lens in the top of the unit. These fixes were used to update the inertial navigation system and provided course guidance with an accuracy of at least 90 meters (300 feet). Some current aircraft and missile systems use improved versions as a backup to GPS.")

[2] https://directory.eoportal.org/web/eoportal/satellite-missio... (ISS Utilization: NICER/SEXTANT)

(I have not acquired nor reversed engineering any military grade celestial navigation equipment or systems, please don't sic ITAR on me)

Yup. In the 18th century figuring out a way to get accurate enough time at sea to allow accurate navigation was one of the most pressing problems for the various countries trying to establish themselves as major players in the New World.

Whichever country figured it out first would gain a significant military and economic advantage for as long as they could keep it secret.

An excellent book about this is "Longitude" by Dava Sobel [1].

[1] https://en.wikipedia.org/wiki/Longitude_(book)

With two points that should narrow down the position to two possible locations (with rather large uncertainty).

Edit: thinking about it further knowing north would reduce it down to 1 point. You also need to know where you are in the world to know which way magnetic north is pointing. It would be 1 very fuzzy spot.

If you find Polaris, you have both a vector to north and an angle to calculate latitude. No other info needed for that.

So you only need 1 overhead star plus a clock to figure out approx longitude.

Magnetic north is only useful if you need help finding Polaris.

For celestial objects, The math is rather simple. It is the intersection of 2 circles. The refence between the two objects would resolve which intersection is the correct one.

For magnetic north and 1 celestial object, the math is much more complex. Magnetic declination changes depending on where you are. You have to know roughly where you are before you start using it.

Polaris is important because it doesn't move, relative to the rest of the sky rotating around it.

You measure the angle from Polaris to geodetic "up" and that's the complimentary angle to your latitude. There is no complex math, just 90-x=y

If you have the time in London, and can observe the sun at its peak (solar noon) then you have longitude (after converting hours to degrees, and keeping minutes and seconds).

Or with an almanac, you can measure pretty much any known ID'd star or the sun at any time, and look up longitude from that.

Reinventing the wheel isn't needed, it's been the same process for centuries.

Whether the instruments being used are precise enough for any of this to matter is a different story. I’m quite curious whether military clocks correct their own relativistic errors. Military satellites almost certainly do.

It's not that they can or can't make adjustments vs any other standard of keeping time, it's that they don't have to.

Whatever may (or may not) make sense today, we adjust to Navy time, because that's what's official, and that's what GPS time is ultimately based on.

Re, relativistic corrections, I don't know the answer for sure, but they average the time between multiple (I think cesium?) atomic clocks. If those clocks all shared the ~same reference frame, I'd think, by definition, you'd not need to make a relativistic adjustment. The frame you'd reference to is the one you're already in.

Doesn't it convert to within some margin for error? Checking Wikipedia, I see that the delta between TAI and Unix time has only drifted 27 seconds since 1972. That should be more than sufficient for your average mundane human readable purpose.

It's easier to just keep high noon at the Greenwich observatory as the defining datum, since most worldwide coordinates ultimately reference back to it, being 0deg longitude.

Ultimately, either time or location would need to be adjusted, and it's easier to do time. Plus it's consistent with what's been done historically.

And this kind of thing can never be undone. See: NTSC "60" Hz actually being 59.94 Hz due to the transition between black and white and color TV. Monitors today still have this lasting effect for consistency's sake.

But those dozen IT people think the trade off is really worth it (for them)!

https://en.wikipedia.org/wiki/Leap_second#International_prop...