Orientation with a Viking sun-compass, a shadow-stick, and two calcite sunstones under various weather conditions
Summary (1 min read)
Greenland and Newfoundland without knowing about
- Based hyperbolic gnomonic line right under the shadow on this artifact, it has been hypothesized that Vikings tip.
- The major axis of the hyperbola points toward the true North.
- Sunstones are hypothesized to be dichroic crystals (e.g., tourmaline or cordierite) or birefringent crystals (e.g., calcite), that can be used to identify the direction of polarization of skylight [6, [14] [15] [16] .
- Theoretically, Vikings could use such a primitive skylight polarimetry to locate the occluded sun and use this information for navigation [6, 8, 15, 16] .
- The authors demonstrate here that the solar elevation angle can be assessed with satisfying accuracy even without dedicated instruments, and the shadow-stick functions perfectly in situations when the sun position can be estimated by the naked eye.
2. Materials and Methods
- (ii) The solar elevation angle was estimated either with bare hands, or with the round shield [Figs. 1E and 1F ]. (iii).
- The sun-compass was rotated until the gnomonic line fitted to the shadow tip, or to the tip of the shadow-stick, which pointed toward the presumed antisolar meridian [Figs. 1C and 1D ].
- After orientation, an assistant removed the cover of the magnetic compass without turning the dial-plate and took a photograph with a digital camera (Nikon CoolPix 8700) looking at the dial-plate in normal angle from 60 cm above it.
- The direction aand the length rof the mean vector of the directional angles considered as North were calculated.
- The uniformity of the directional angles considered as North was tested by Rayleigh test on the mean vector separately in all four weather categories.
4. Discussion
- On the other hand, the authors showed that calcite sunstones could not be used to locating the occluded sun in the overcast sky, this task requires more sophisticated instruments.
- If sunstones were used by medieval navigators, they could rather use them in periods when the sun was below the horizon, but clear patches of the sky could be seen [15, 16, 23] .
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Citations
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Cites methods from "Orientation with a Viking sun-compa..."
...By using a 2-component magnetic compass, we can obtain equation (7) as shown in Fig....
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...By substituting equation (6) and equation (7) forv and As respectively into equation (5), and ignoring the little deviation between UTC and UT1 we obtain equations (8) and (9)....
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References
42 citations
"Orientation with a Viking sun-compa..." refers background or methods in this paper
...Theoretically, Vikings could use such a primitive skylight polarimetry to locate the occluded sun and use this information for navigation [6,8,15,16]....
[...]
...Theoretically, the contrast sensitivity of the human eye should allow human observers to use calcite sunstones to identify the direction of polarization of light with an accuracy of 1°, even if its degree of polarization is very low [15]....
[...]
...If sunstones were used by medieval navigators, they could rather use them in periods when the sun was below the horizon, but clear patches of the sky could be seen [15,16,23]....
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...Calcite sunstones, forming the third element of our hypothesized toolkit, failed to increase the accuracy of orientation, although theoretical calculations, polarimetric surveys, and laboratory measurements predicted the contrary [12,13,15]....
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35 citations
"Orientation with a Viking sun-compa..." refers background in this paper
...Roslund and Beckman [18] criticized this theory, suggesting that the sun can be located inmost situations without skylight polarimetry, but the psychophysical survey by Barta et al....
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...Roslund and Beckman [18] criticized this theory, suggesting that the sun can be located inmost situations without skylight polarimetry, but the psychophysical survey by Barta et al. [19] proved that such estimations are unreliable....
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20 citations
Additional excerpts
...[19] proved that such estimations are unreliable....
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