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Today I learned about the existence of the "gyrocompass".

A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and rotation of the Earth (or another planetary body if used elsewhere in the universe) to automatically find geographical direction (normally, true North).

It seems that these kind of compasses are better than regular compasses (especially when you want to orient yourself or to find true North) as they are not affected by ferromagnetic materials.

In spite of being objectively better than regular compasses, I had not heard of them until today. I believed there was only one type of compass (the magnetic one we all know).

I am wondering if there exist any other kind of compasses (magnetic or not) useful for navigation in particular, besides these two (the regular one and the gyrocompass) and also, which of them is the best for said purpose.

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    Gyrocompasses are better in some ways, but they have some severe drawbacks, especially in terms of precession. – Rory Alsop Feb 11 '17 at 21:44
  • Supplementing what @RoryAlsop said, "objectively better" is a very strong claim; in particular the wiki's statement about "cannot ordinarily be used for long-term marine navigation" shows one important way they're not "objectively better." – Kevin Feb 13 '17 at 3:15
  • Any hand-held "electronic" compass is likely a solid-state magnetic compass, using the Hall Effect to measure the Earth's magnetic field. Gyrocompasses (suitably corrected for precession) are useful in boats, but are not portable enough (especially when the power source is included) for most of our outdoor activities. – Toby Speight Feb 13 '17 at 11:03
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Beyond the ones you have mentioned, there are,

Solar Compasses

The solar compass, a surveying instrument that makes use of the sun's direction, was first invented and made by William Austin Burt.1

Burt’s solar compass is a precision instrument made of brass with a solar attachment that allows surveyors to determine the true north direction by reference to the sun rather than by reference to the magnetic north pole.[5]

It allowed surveyors to locate true north through viewing the sun and other astronomical observations and was not influenced by magnetism or iron ore or other ore materials.[3]

and,

Astrocompass

An astrocompass is a navigational tool for determining the direction of true north through the positions of various astronomical bodies.

There are certain circumstances when magnetic compasses and gyrocompasses are unreliable. The most obvious is in polar regions, where the force exerted on the needle of a magnetic compass is nearly vertical and gyrocompasses become unstable due to the rotation of the Earth. Magnetic compasses are also susceptible to disruption from magnetic fields other than the Earth's, such as those produced by the hulls of some metal vehicles or craft. Before the advent of electronic navigational aids such as GPS the most reliable way to ascertain north in such circumstances was through the use of an astrocompass.

As for which is best, that will depend on you usage and location. Some could be better and some worse depending on the situation.

  • I assume this form of solar compass needs an accurate local time to work. – Chris H Feb 12 '17 at 11:53
  • @ChrisH If you read the wiki description it only says aproximate local time – Charlie Brumbaugh Feb 12 '17 at 18:57
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There are some very crude outdoor compasses which tell us the direction of true north (and assume we can estimate angles from north). The following also assume we're in the northern hemisphere.

A sun-stick-shadow compass: If the sun shines, place a vertical stick in the ground. Every 15 minutes or so, mark the end of the stick's shadow. The line of shadow marks will lie in a west-to-east direction. And if you happen to do this at mid-day, the very shortest shadow points south.

A crescent moon compass: A morning moon looking like this "(" will have its bulge pointing east and an evening moon looking like this ")" will have its bulge pointing west. And the moon will be roughly in the south. More accurately, south is where a line joining the "horns" of the crescent extends down to and meets the horizon.

The pole star compass: On a clear night the star called Polaris is virtually exactly pointing north. (Not part of the question but useful to know: the elevation angle of Polaris above the horizon is your latitude.)

4

An analogue watch makes a useful compass combined with the sun. I've used this to good effect in cities as well as open country. This link is actually to a rather imprecise method. A more accurate way is given in a book I have, but requires a table of angles.

Of course if you only have a digital watch you can draw or imagine the equivalent analogue face.

3

In cartography, the concept of True North may be slightly different in different parts of the county, the state, or the country. When cartographers got together many years ago to hash out some of their different practices, they decided to essentially invent a system that would describe the earth's surface as an approximation of a spheroid.

They came up with the geoid. You are actually pretty familiar with one of the more recent geoids, because its ubiquity is now such that it is a part of your life.

That's because the US Navy, years ago, thought that their current navigation systems were a hodgepodge of ancient relics and technology that was ridiculous. And inaccurate. Even their early version of satellite navigation was pathetic. So they put a few satellites in the air and called the system NAVSTAR. You might know it as the Global Positioning System, GPS.

And so while naval vessels certainly have gyrocompasses galore, and they can break out the old celestial navigation instruments and books, the go-to way of determining position and compass heading is with very fast and very accurate position fixes from GPS.

But going back to the geoid, which is going to be "WGS 84" (1984) for most GPS fixes, the cartographers were able to successfully correlate a local position with a global position. So if "north" in Fairfax county is a few minutes off of true north, or if the "latitude" of positions in Arlington County tends to be 24.3 m south of the global geoid, then a cartographer can account for this.

So if a position needs to be offset in one region, and stretched in another region, the reference geoid is used for the "conversion" as bearing lines pass from one place to another. You will discover that most insular areas of a country have historical boundaries and waterways which are peculiar to that country. So in the US, there is a place allegedly called "Four Corners," which separates for states. It was pinpointed about "1807 feet east of where it should have been placed in 1875."

So to get back to your question, you may be surprised to learn that some old surveyors used literal links and chains, and that sometimes their compass was no more than the apparent line of sight from a "known" position to an unknown position that was halfway to another "known" position.

And due to historical errors, the "north-south" property line or the east-west state line near you could be a jagged, seemingly arbitrary, non-true anything.

One of the old types of satellite navigation which I failed to mention earlier utilized satellites in polar orbit. This type of orbit is quite a useful one, especially for cartography and communication. You can use this type of satellite on a clear night to find a north-south line. So while you may know how to do celestial navigation, or be able to follow a pole star, a satellite in low polar orbit will be visible, rapidly transiting the sky from north to south. This works in both hemispheres, too, in case you find yourself way down under.

So that gives you three more virtual compasses: 1. the cartographer's and surveyor's grid coordinate systems that trickle down to us as fence lines and national borders. 2. the geoid-inspired compass that's on your cell phone. And 3. the north-south path of polar orbiting satellites. #1 and #3 can be used without carrying anything with you.

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    Welcome uruiamme - cool answer! How do I determine the north-south path of polar orbiting satellites without any equipment? – imsodin Feb 12 '17 at 17:21
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    Do you have a source for the old type of satellite navigation? When and where was this used? As far as I understand, one can only see satellites around sunset /sunrise, so not during the night proper. And if I look up at a random position on the globe hoping to catch a satellite at the right time it might be an eastward traveling one. How would one know the difference between a polar and a non-polar satellite? – user2705196 Feb 12 '17 at 18:07
  • For imsodin, You will observe many things in the night sky besides the polar-orbiting satellites. In the Northern Hemisphere, we recognize Polaris as the North "Pole" star. This will get you started. Otherwise, the east-west drift of the moon across the ecliptic will orient you, too. Carefully observing the "rise" and "set" of any solar system object (the 4 brightest planets plus the moon) will give you east or west. Polar orbits cross this. At dawn and dusk, the brightest part of the sky is lit by the sun in the east or west, respectively. – uruiamme Feb 12 '17 at 21:43
  • You can look up the old US Navy System by reading the history of GPS at Wikipedia. The system was called TRANSIT, essentially because the Navy receivers used the Doppler Effect and lookup tables to obtain a fix from the transiting satellites. – uruiamme Feb 12 '17 at 21:46
  • For user2705196 You can look up the old US Navy System by reading the history of GPS at Wikipedia. The system was called TRANSIT, essentially because the Navy receivers used the Doppler Effect and lookup tables to obtain a fix from the transiting satellites. These satellites, like other (typically military) satellites tend to move extremely fast and all night. They can be mistaken for a "shooting star" although they are faint. And before/concurrent with TRANSIT, the Navy used LORAN, which was junk, which used land-based transmitters. To determine rough N-S direction, see my other comment. – uruiamme Feb 12 '17 at 21:52

protected by Charlie Brumbaugh Jun 28 '18 at 22:09

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