8 ms·

Exactly how would this work when the sun has set?

by rexreed 14y ago

colanderman 14y ago
I'm assuming they mean during twilight (i.e. after the sun has set but before it has ceased to illuminate the local atmosphere).
rua12yearold 14y ago
Did you know that in summer toward the Arctic Circle the Sun sets but it does not get dark? It is about as light as a cloudy day, all night long.
defrost 14y ago
The sun below the horizon is still a source of diffuse light, the crystal is used to find the angle to a source of light and in northern latitudes with long twilights the sun produces a glow long after it has set. See: http://www.livescience.com/16831-viking-sunstone-crystal-compass.html http://www.livescience.com/16831-viking-sunstone-crystal-com...
- contingencies 14y ago
  Nice. First 3D-printed replica wins my vote as a teaching aid and generally cool retro hack. We need more of this offline tech stuff. Combine a compass and other navigational tools, and I see an interesting evolution as a sort of retro, creative-commons, git-forkable hacker-army object.
  - jff 14y ago
    When you figure out how to 3d print a birefringent material, let me know. In fact, when you get a hobby-grade 3d printer to print something you can actually see through, let me know.
    - contingencies 14y ago
      Sure. Obviously not everything comes from a machine. One can probably rely on people finding some crystal separately and/or if feasible order bulk-printed 3D transparent material (no idea of light properties of those, though I know they exist... just saw some this morning!).
      - jff 14y ago
        If you find the crystal separately, there's nothing left to print. The tool is fully functional as nothing more than a lump of crystal.
        contingencies 14y ago
        My understanding from the image is that the operation is based upon the combination of two directional light beams through holes driven by an opaque piece with a rotating disc. Whether this was used at the time or not, it still seems a clear way to demonstrate the concepts. At the very least the operation could perhaps be usefully modelled three dimensionally using raytracing, perhaps also with the capacity to vary basic optical properties of the transparent crystal feature such as reflectiveness, refractiveness and average opacity, as well as atmospheric conditions encountered in the seas ancient European seafaring peoples are known to have sailed.
  - keithpeter 14y ago
    OK, have a look at the Bris 'sextant'. http://en.wikipedia.org/wiki/Bris_sextant http://en.wikipedia.org/wiki/Bris_sextant Elegant device that enables you to get an accurate Sun altitude at specific times of day, and hence a position fix. No moving parts. I think the 'hack' here is to think through the navigation requirements of someone sailing across an ocean. Do they need to be able to find a position at an arbitrary time (the proper sextant) or would the ability to find a position at some time during daylight be enough? The result is a device that is robust and that can be kept in a 35mm film cassette.
- splitbrain 14y ago
  So it depends on polarizing the sun light, right? Could one build something like this from a typical polarizing camera filter? Would it need a linear or circular filter? I guess the former.
- ryandvm 14y ago
  I think the claim that this could be used at dusk and twilight is a little silly. Maybe it could have, but then again, figuring out where the sun just set, even under cloud cover, doesn't exactly require a "sunstone". (Hint: it's that glowy part of the sky.)
  - Zikes 14y ago
    The key here is that it is within a few degrees, which make a huge difference over long distances on the sea.
BerislavLopac 14y ago
According to the Wikipedia article on the Iceland spar (http://en.wikipedia.org/wiki/Iceland_spar http://en.wikipedia.org/wiki/Iceland_spar): "Further research in 2011 by Ropers et al., confirms that identifying the direction of the sun to within a few degrees in both cloudy and twilight conditions was possible using the sunstone and the naked eye." So it could probably work closely after sunset or before sunrise, but not at night.
- gtufano 14y ago
  Well, they probably sailed mostly on summer (because of weather) when, at northern latitudes, twilight conditions are persistent for most of the "night".

Exactly how would this work when the sun has set?

by rexreed 14y ago

Exactly how would this work when the sun has set?

I'm assuming they mean during twilight (i.e. after the sun has set but before it has ceased to illuminate the local atmosphere).

rua12yearold 14y ago

Did you know that in summer toward the Arctic Circle the Sun sets but it does not get dark? It is about as light as a cloudy day, all night long.

defrost 14y ago

The sun below the horizon is still a source of diffuse light, the crystal is used to find the angle to a source of light and in northern latitudes with long twilights the sun produces a glow long after it has set. See: http://www.livescience.com/16831-viking-sunstone-crystal-compass.html http://www.livescience.com/16831-viking-sunstone-crystal-com...

contingencies 14y ago
Nice. First 3D-printed replica wins my vote as a teaching aid and generally cool retro hack. We need more of this offline tech stuff. Combine a compass and other navigational tools, and I see an interesting evolution as a sort of retro, creative-commons, git-forkable hacker-army object.
- jff 14y ago
  When you figure out how to 3d print a birefringent material, let me know. In fact, when you get a hobby-grade 3d printer to print something you can actually see through, let me know.
  - contingencies 14y ago
    Sure. Obviously not everything comes from a machine. One can probably rely on people finding some crystal separately and/or if feasible order bulk-printed 3D transparent material (no idea of light properties of those, though I know they exist... just saw some this morning!).
    - jff 14y ago
      If you find the crystal separately, there's nothing left to print. The tool is fully functional as nothing more than a lump of crystal.
      - contingencies 14y ago
        My understanding from the image is that the operation is based upon the combination of two directional light beams through holes driven by an opaque piece with a rotating disc. Whether this was used at the time or not, it still seems a clear way to demonstrate the concepts. At the very least the operation could perhaps be usefully modelled three dimensionally using raytracing, perhaps also with the capacity to vary basic optical properties of the transparent crystal feature such as reflectiveness, refractiveness and average opacity, as well as atmospheric conditions encountered in the seas ancient European seafaring peoples are known to have sailed.
- keithpeter 14y ago
  OK, have a look at the Bris 'sextant'. http://en.wikipedia.org/wiki/Bris_sextant http://en.wikipedia.org/wiki/Bris_sextant Elegant device that enables you to get an accurate Sun altitude at specific times of day, and hence a position fix. No moving parts. I think the 'hack' here is to think through the navigation requirements of someone sailing across an ocean. Do they need to be able to find a position at an arbitrary time (the proper sextant) or would the ability to find a position at some time during daylight be enough? The result is a device that is robust and that can be kept in a 35mm film cassette.
splitbrain 14y ago
So it depends on polarizing the sun light, right? Could one build something like this from a typical polarizing camera filter? Would it need a linear or circular filter? I guess the former.
ryandvm 14y ago
I think the claim that this could be used at dusk and twilight is a little silly. Maybe it could have, but then again, figuring out where the sun just set, even under cloud cover, doesn't exactly require a "sunstone". (Hint: it's that glowy part of the sky.)
- Zikes 14y ago
  The key here is that it is within a few degrees, which make a huge difference over long distances on the sea.

BerislavLopac 14y ago

According to the Wikipedia article on the Iceland spar (http://en.wikipedia.org/wiki/Iceland_spar http://en.wikipedia.org/wiki/Iceland_spar): "Further research in 2011 by Ropers et al., confirms that identifying the direction of the sun to within a few degrees in both cloudy and twilight conditions was possible using the sunstone and the naked eye." So it could probably work closely after sunset or before sunrise, but not at night.

gtufano 14y ago
Well, they probably sailed mostly on summer (because of weather) when, at northern latitudes, twilight conditions are persistent for most of the "night".