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I'm looking to get started in basic celestial navigation, but I live in Colorado1. The first problem that gives me is the absence of an accurate horizon in any direction. To help address this I bought an "artificial horizon", which essentially consists of a small pot of water which creates an accurate reflection of the Sun such that determining the angle between the Sun and the image will give me exactly twice the altitude of the sun above horizontal. Unfortunately at this time of year and this latitude, the result is an angle far too great for the sextant to span at noon.

I'm wondering if there is another mechanism that I might use for taking sights while I start to practice. So far the nearest I've come up with, which involves expense I would prefer to avoid, is to get a laser level and somehow use that. It's far from obvious to me how I would make this work however.

Can anyone suggest something that I might be able to use to get a workably decent horizon reference under these circumstances? Or do I just have to wait until either the winter, or I find myself traveling to a place where ocean is visible?


1for example The Front Range of the Rocky Mountains near Denver, Colorado

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There are relatively simple practice bubble levels available for most sextants. I have used one of this type, consisting of a tube and bubble that replaces the standard eyepiece/telescope. It cannot be used in the dark since the bubble is unlit, but is ok for practice with the sun, or bright stars at the early part of twilight. It is a bit awkward to hold steady, and not recommended for navigation since accuracy is degraded by a couple of arc minutes.

I usually had more consistent results practicing from the shore or dock, but I live near the ocean. You might be able try sighting over a body of water like a lake or river to get a consistent level, even if the actual horizon is not visible.

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  • $\begingroup$ that's interesting thank you. Mine is the venerable (cheap!) Davis Mark 3, which I think is too low end to provide such an option. I shall, however, look around. And at the least it's good to know that such an option exists if I get to the point of upgrading. $\endgroup$ May 21, 2023 at 17:09
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You should divide up your practice and not focus so much on a noon sight. You can practice taking measurements with the sextant at any time, and verify it with planetarium software. Same with the mathematics part, take the readings from planetarium software, and use those to compute the position. Waiting to arrange perfect conditions will only limit the practice you get.

You don't need the ocean or other large body of water to get a horizon line. At 1 meter above the surface (e.g sitting), the horizon is 2.2 miles away. And 2 meters above the surface (e.g standing), the horizon is 3.1 miles away. And you can wade out into the water to get an even closer horizon. There may be trees or hills poking above the horizon, but they can simply be ignored.

Other options are to use the artificial horizon, but on lower objects like the stars, planets and the moon. You can also use a mirror (best to have a front surfaced mirror), and tilt it at a known angle (actually doing that can be tough to do accurately though), and use that as an artificial horizon. It's also possible to use a small body of water without a horizon, and just compute how much the far edge is below where the horizon would be.

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    $\begingroup$ I'm 1600 metres, 1 mile) above sea level, with 3000 metre moutains on one side of me (solid, north through south, it's the U.S. continental divide), and as steady descent of unknown (and naturally inconsistent) gradient in the other. There are some reservoirs (with dams all around, since they are flooded rivers), but they're around an hour's drive away, so not really conducive to a quick trip to try something out, and I can't arrange to be there at noon anyway. I know other bodies can be used, but since 'm completely new to this I would like to start with the sun at noon. $\endgroup$ May 21, 2023 at 20:27
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    $\begingroup$ You should divide up your practice and not focus so much on a noon sight. You can practice taking measurements with the sextant at any time, and verify it with planetarium software. Same with the mathematics part, take the readings from planetarium software, and use those to compute the position. Waiting to arrange perfect conditions will only limit the practice you get. $\endgroup$ May 22, 2023 at 4:04
  • $\begingroup$ Ah, that's an excellent plan, thanks. Would you like to make an answer of that, so I can accept it? $\endgroup$ May 22, 2023 at 11:32
  • $\begingroup$ I'll just add it to this one. $\endgroup$ May 22, 2023 at 12:39

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