Abstract

The Norse discovery of Greenland is associated with the sighting of low barren islands called Gunnbjörn’s Skerries, which have never been satisfactorily identified. Here the historical references that connect the skerries to Greenland are reviewed. A mirage of the Greenland coast, arising specifically from optical ducting under a sharp temperature inversion, is used to explain the vision of skerries seen by the Norse mariners. Images from both ducting and uniform inversions are calculated. Under the assumption of a clean Rayleigh atmosphere, sufficient visibility remains to see the skerry image at a distance of 220 km. There is significant circumstantial evidence to indicate that the Norse were familiar with the skerrylike mirage and that they used it to discover new lands.

© 2000 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. G. Jones, The Norse Atlantic Saga (Oxford, London, 1964).
  2. K. Gjerset, History of Iceland (MacMillan, New York, 1924).
  3. F. Nansen, In Northern Mists, 2 Vols. (Heinemann, London, 1911; reprinted by AMS New York, 1969).
  4. F. Gad, The History of Greenland I: Earliest Times to 1700 (Hurst, London, 1970).
  5. K. A. Seaver, The Frozen Echo (Stanford University, Stanford, Calif., 1996).
  6. In Ref. 3, Vol. 1, p. 263, Nansen quotes Björn Jónsson’s Grönlands Annaler (1625) from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 88.
  7. G. Holm, “Gunbjørns-Skær og Korsøer,” Medd. Groenl. 56, 291–308 (1918), p. 292. Holm quotes from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 105.
  8. Ref. 1; p. 129.
  9. Ref. 1; 165.
  10. The Blosseville Coast consists of very high mountains (the Watkins Range), the highest of which, Gunnbjörns Fjæld, exceeds 3900 m.
  11. All geographical information is taken from the global digital elevation model GTOPO30. This public-domain digital elevation model, which covers the globe at a resolution of 30 arc sec, is obtainable at http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html . The map and the perspective images of Fig. 2 are produced with Generic Mapping Tools Version 3.2 (available from http://www.soest.hawaii.edu/gmt ). See also P. Wessel, W. H. F. Smith, “New, improved version of the Generic Mapping Tools released,” Eos Trans. Am. Geophys. Union 79, 579 (1998).
  12. J. Kr. Tornøe, “Hvitserk og Blåserk,” Nor. Geogr. Tidskr. 5, 429–443 (1935).
    [CrossRef]
  13. M. K. Hughes, H. F. Diaz, eds., “The Medieval Warm Period,” Clim. Change 26, 109–342 (1994).
  14. J. Jóhannesson, A History of the Old Icelandic Commonwealth (University of Manitoba, Winnipeg, Canada, 1974), pp. 106–107.
  15. Mt. Rigny, a mountain of elevation 2470 m, is located 35 km inland from the Greenland coast, nearly along the shortest line of sight from Iceland to Greenland. Its distance from Snæfjall (793 m) in Iceland is 357 km. In the standard atmosphere the horizon distance d (km) from either peak is approximately d = 3.9 h, where h is the elevation in meters. For an observer whose eye elevation is 3 m, a ray tangent to the horizon would meet the tips of Snæfjall and Mt. Rigny at distances 117 km and 201 km, respectively. The gap in intervisibility is thus 39 km. However, the distance to be sailed without a comfortable view of land (say, 5 arc min high) is somewhat longer, 62 km.
  16. J. Först, “Geschichte der Entdeckung Grönlands,” Ph.D. dissertation (Friedrich-Alexanders-Universität Erlangen, Erlangen, Germany, 1906), p. 9.
  17. Ref. 3, Vol. 1, p. 262; the account of Ivar Bardsson.
  18. W. H. Lehn, I. I. Schroeder, “Polar mirages as aids to Norse navigation,” Polarforschung 49, 173–187 (1979).
  19. Ref. 1, p. 38.
  20. J. M. Grove, The Little Ice Age (Methuen, London, 1988).
    [CrossRef]
  21. In Ref. 7, p. 298, Holm quotes Björn Jónsson’s Grönlands Annaler (1625) from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 127.
  22. John Ross, A Voyage of Discovery (Murray, London, 1819).
  23. W. H. Lehn, “The Novaya Zemlya effect: an arctic mirage,” J. Opt. Soc. Am. 69, 776–781 (1979).
    [CrossRef]
  24. F. Nansen, In Nacht und Eis (Die Norwegische Polarexpedition 1893–1896) (Brockhaus, Leipzig, 1897), Vol. 1, pp. 315–316.
  25. E. H. Shackleton, South–The Story of Shackleton’s Last Expedition 1914–1917 (MacMillan, New York, 1920), p. 49.
  26. G. H. Liljequist, “Refraction phenomena in the polar Atmosphere,” in Scientific Results: Norwegian–British–Swedish Antarctic Expedition 1949–1952 (Oslo University, Oslo, 1964), Vol. 2, Part 2.
  27. W. H. Lehn, W. Friesen, “Simulation of mirages,” Appl. Opt. 31, 1267–1273 (1992).
    [CrossRef] [PubMed]
  28. S. R. Church, “Atmospheric mirage and distortion modeling for IR target injection simulations,” in Meeting on Targets and Backgrounds: Characterization and Representation II, W. R. Watkins, ed., Proc. SPIE2742, 122–135 (1996).
  29. R. Cleasby, G. Vigfusson, An Icelandic/English Dictionary, 2nd ed. (Clarendon, Oxford, 1957). The word hillingar is defined as “upheaving, esp. of a mirage, when rocks and islands look as if lifted above the level of the sea.”
  30. T. Búason, “Mirages and vertical contraction of images of distant objects,” P.O. Box 273, 101 Reykjavik, Iceland (personal communication, 1998).
  31. W. H. Lehn, T. L. Legal, “Long-range superior mirages,” Appl. Opt. 37, 1489–1494 (1998).
    [CrossRef]
  32. G. Wyszecki, W. S. Stiles, Color Science, 2nd ed. (Wiley, New York, 1982), p. 569.
  33. W. G. Driscoll, W. Vaughan, eds., Handbook of Optics (McGraw-Hill, New York, 1978).
  34. G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.
  35. F. Baur, Meteorologisches Taschenbuch (Akademische Verlagsgesellschaft, Leipzig, 1970), Vol. 2, p. 525.
  36. M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1986), p. 95.
  37. W. E. K. Middleton, “Vision through the Atmosphere,” Handbuch der Physik (Springer, Berlin, 1957), Vol. 48, pp. 254–287. The distance at which the transmission factor equals 0.02 (the minimum contrast detectable by the human eye) gives Koschmieder’s visual range for a black object.

1998 (1)

1994 (1)

M. K. Hughes, H. F. Diaz, eds., “The Medieval Warm Period,” Clim. Change 26, 109–342 (1994).

1992 (1)

1980 (1)

G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.

1979 (2)

W. H. Lehn, I. I. Schroeder, “Polar mirages as aids to Norse navigation,” Polarforschung 49, 173–187 (1979).

W. H. Lehn, “The Novaya Zemlya effect: an arctic mirage,” J. Opt. Soc. Am. 69, 776–781 (1979).
[CrossRef]

1935 (1)

J. Kr. Tornøe, “Hvitserk og Blåserk,” Nor. Geogr. Tidskr. 5, 429–443 (1935).
[CrossRef]

1918 (1)

G. Holm, “Gunbjørns-Skær og Korsøer,” Medd. Groenl. 56, 291–308 (1918), p. 292. Holm quotes from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 105.

Baur, F.

F. Baur, Meteorologisches Taschenbuch (Akademische Verlagsgesellschaft, Leipzig, 1970), Vol. 2, p. 525.

Born, M.

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1986), p. 95.

Búason, T.

T. Búason, “Mirages and vertical contraction of images of distant objects,” P.O. Box 273, 101 Reykjavik, Iceland (personal communication, 1998).

Church, S. R.

S. R. Church, “Atmospheric mirage and distortion modeling for IR target injection simulations,” in Meeting on Targets and Backgrounds: Characterization and Representation II, W. R. Watkins, ed., Proc. SPIE2742, 122–135 (1996).

Cleasby, R.

R. Cleasby, G. Vigfusson, An Icelandic/English Dictionary, 2nd ed. (Clarendon, Oxford, 1957). The word hillingar is defined as “upheaving, esp. of a mirage, when rocks and islands look as if lifted above the level of the sea.”

Cosden, T. H.

G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.

Först, J.

J. Först, “Geschichte der Entdeckung Grönlands,” Ph.D. dissertation (Friedrich-Alexanders-Universität Erlangen, Erlangen, Germany, 1906), p. 9.

Friesen, W.

Gad, F.

F. Gad, The History of Greenland I: Earliest Times to 1700 (Hurst, London, 1970).

Gjerset, K.

K. Gjerset, History of Iceland (MacMillan, New York, 1924).

Grove, J. M.

J. M. Grove, The Little Ice Age (Methuen, London, 1988).
[CrossRef]

Holm, G.

G. Holm, “Gunbjørns-Skær og Korsøer,” Medd. Groenl. 56, 291–308 (1918), p. 292. Holm quotes from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 105.

Jóhannesson, J.

J. Jóhannesson, A History of the Old Icelandic Commonwealth (University of Manitoba, Winnipeg, Canada, 1974), pp. 106–107.

Jones, G.

G. Jones, The Norse Atlantic Saga (Oxford, London, 1964).

Legal, T. L.

Lehn, W. H.

Liljequist, G. H.

G. H. Liljequist, “Refraction phenomena in the polar Atmosphere,” in Scientific Results: Norwegian–British–Swedish Antarctic Expedition 1949–1952 (Oslo University, Oslo, 1964), Vol. 2, Part 2.

Middleton, W. E. K.

W. E. K. Middleton, “Vision through the Atmosphere,” Handbuch der Physik (Springer, Berlin, 1957), Vol. 48, pp. 254–287. The distance at which the transmission factor equals 0.02 (the minimum contrast detectable by the human eye) gives Koschmieder’s visual range for a black object.

Nansen, F.

F. Nansen, In Nacht und Eis (Die Norwegische Polarexpedition 1893–1896) (Brockhaus, Leipzig, 1897), Vol. 1, pp. 315–316.

F. Nansen, In Northern Mists, 2 Vols. (Heinemann, London, 1911; reprinted by AMS New York, 1969).

Ross, John

John Ross, A Voyage of Discovery (Murray, London, 1819).

Schroeder, I. I.

W. H. Lehn, I. I. Schroeder, “Polar mirages as aids to Norse navigation,” Polarforschung 49, 173–187 (1979).

Seaver, K. A.

K. A. Seaver, The Frozen Echo (Stanford University, Stanford, Calif., 1996).

Shackleton, E. H.

E. H. Shackleton, South–The Story of Shackleton’s Last Expedition 1914–1917 (MacMillan, New York, 1920), p. 49.

Stiles, W. S.

G. Wyszecki, W. S. Stiles, Color Science, 2nd ed. (Wiley, New York, 1982), p. 569.

Tornøe, J. Kr.

J. Kr. Tornøe, “Hvitserk og Blåserk,” Nor. Geogr. Tidskr. 5, 429–443 (1935).
[CrossRef]

Trusty, G. L.

G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.

Vigfusson, G.

R. Cleasby, G. Vigfusson, An Icelandic/English Dictionary, 2nd ed. (Clarendon, Oxford, 1957). The word hillingar is defined as “upheaving, esp. of a mirage, when rocks and islands look as if lifted above the level of the sea.”

Wolf, E.

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1986), p. 95.

Wyszecki, G.

G. Wyszecki, W. S. Stiles, Color Science, 2nd ed. (Wiley, New York, 1982), p. 569.

Appl. Opt. (2)

Clim. Change (1)

M. K. Hughes, H. F. Diaz, eds., “The Medieval Warm Period,” Clim. Change 26, 109–342 (1994).

J. Opt. Soc. Am. (2)

G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.

W. H. Lehn, “The Novaya Zemlya effect: an arctic mirage,” J. Opt. Soc. Am. 69, 776–781 (1979).
[CrossRef]

Medd. Groenl. (1)

G. Holm, “Gunbjørns-Skær og Korsøer,” Medd. Groenl. 56, 291–308 (1918), p. 292. Holm quotes from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 105.

Nor. Geogr. Tidskr. (1)

J. Kr. Tornøe, “Hvitserk og Blåserk,” Nor. Geogr. Tidskr. 5, 429–443 (1935).
[CrossRef]

Polarforschung (1)

W. H. Lehn, I. I. Schroeder, “Polar mirages as aids to Norse navigation,” Polarforschung 49, 173–187 (1979).

Other (29)

Ref. 1, p. 38.

J. M. Grove, The Little Ice Age (Methuen, London, 1988).
[CrossRef]

In Ref. 7, p. 298, Holm quotes Björn Jónsson’s Grönlands Annaler (1625) from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 127.

John Ross, A Voyage of Discovery (Murray, London, 1819).

J. Jóhannesson, A History of the Old Icelandic Commonwealth (University of Manitoba, Winnipeg, Canada, 1974), pp. 106–107.

Mt. Rigny, a mountain of elevation 2470 m, is located 35 km inland from the Greenland coast, nearly along the shortest line of sight from Iceland to Greenland. Its distance from Snæfjall (793 m) in Iceland is 357 km. In the standard atmosphere the horizon distance d (km) from either peak is approximately d = 3.9 h, where h is the elevation in meters. For an observer whose eye elevation is 3 m, a ray tangent to the horizon would meet the tips of Snæfjall and Mt. Rigny at distances 117 km and 201 km, respectively. The gap in intervisibility is thus 39 km. However, the distance to be sailed without a comfortable view of land (say, 5 arc min high) is somewhat longer, 62 km.

J. Först, “Geschichte der Entdeckung Grönlands,” Ph.D. dissertation (Friedrich-Alexanders-Universität Erlangen, Erlangen, Germany, 1906), p. 9.

Ref. 3, Vol. 1, p. 262; the account of Ivar Bardsson.

Ref. 1; p. 129.

Ref. 1; 165.

The Blosseville Coast consists of very high mountains (the Watkins Range), the highest of which, Gunnbjörns Fjæld, exceeds 3900 m.

All geographical information is taken from the global digital elevation model GTOPO30. This public-domain digital elevation model, which covers the globe at a resolution of 30 arc sec, is obtainable at http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html . The map and the perspective images of Fig. 2 are produced with Generic Mapping Tools Version 3.2 (available from http://www.soest.hawaii.edu/gmt ). See also P. Wessel, W. H. F. Smith, “New, improved version of the Generic Mapping Tools released,” Eos Trans. Am. Geophys. Union 79, 579 (1998).

G. Jones, The Norse Atlantic Saga (Oxford, London, 1964).

K. Gjerset, History of Iceland (MacMillan, New York, 1924).

F. Nansen, In Northern Mists, 2 Vols. (Heinemann, London, 1911; reprinted by AMS New York, 1969).

F. Gad, The History of Greenland I: Earliest Times to 1700 (Hurst, London, 1970).

K. A. Seaver, The Frozen Echo (Stanford University, Stanford, Calif., 1996).

In Ref. 3, Vol. 1, p. 263, Nansen quotes Björn Jónsson’s Grönlands Annaler (1625) from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 88.

G. Wyszecki, W. S. Stiles, Color Science, 2nd ed. (Wiley, New York, 1982), p. 569.

W. G. Driscoll, W. Vaughan, eds., Handbook of Optics (McGraw-Hill, New York, 1978).

F. Baur, Meteorologisches Taschenbuch (Akademische Verlagsgesellschaft, Leipzig, 1970), Vol. 2, p. 525.

M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1986), p. 95.

W. E. K. Middleton, “Vision through the Atmosphere,” Handbuch der Physik (Springer, Berlin, 1957), Vol. 48, pp. 254–287. The distance at which the transmission factor equals 0.02 (the minimum contrast detectable by the human eye) gives Koschmieder’s visual range for a black object.

F. Nansen, In Nacht und Eis (Die Norwegische Polarexpedition 1893–1896) (Brockhaus, Leipzig, 1897), Vol. 1, pp. 315–316.

E. H. Shackleton, South–The Story of Shackleton’s Last Expedition 1914–1917 (MacMillan, New York, 1920), p. 49.

G. H. Liljequist, “Refraction phenomena in the polar Atmosphere,” in Scientific Results: Norwegian–British–Swedish Antarctic Expedition 1949–1952 (Oslo University, Oslo, 1964), Vol. 2, Part 2.

S. R. Church, “Atmospheric mirage and distortion modeling for IR target injection simulations,” in Meeting on Targets and Backgrounds: Characterization and Representation II, W. R. Watkins, ed., Proc. SPIE2742, 122–135 (1996).

R. Cleasby, G. Vigfusson, An Icelandic/English Dictionary, 2nd ed. (Clarendon, Oxford, 1957). The word hillingar is defined as “upheaving, esp. of a mirage, when rocks and islands look as if lifted above the level of the sea.”

T. Búason, “Mirages and vertical contraction of images of distant objects,” P.O. Box 273, 101 Reykjavik, Iceland (personal communication, 1998).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (8)

Fig. 1
Fig. 1

The Denmark Strait separates Iceland and Greenland. The dotted line indicates the shortest distance between them, 285 km.

Fig. 2
Fig. 2

Images of the Greenland coast. These perspective views are calculated from GTOPO30 digital elevation data with Generic Mapping Tools software, which considers the Earth to be flat and the observer at infinite distance. (a) The region around Gunnbjörns Fjæld (3940 m), the highest peak in Greenland. (b) Portion of Greenland nearest to Iceland. The tick mark identifies the nearest point, at a distance of 285 km.

Fig. 3
Fig. 3

(a) Profile of a temperature inversion that creates an optical duct. (b) Light rays under a full duct that extends all the way to Greenland. The observer’s eye has an elevation of 3 m at the origin of the distance scale. At the observer the ray elevation angles span the range [-3′, +4′] in 1′ steps. At 220 km the rays intersect the Greenland coast, which rises almost vertically from the sea. The plot is curvature corrected so that the Earth shows as a flat plane. Straight rays then appear to curve upward.

Fig. 4
Fig. 4

Mirage of the nearest part of Greenland, calculated from the image of Fig. 2(b) and the rays of Fig. 3(b). The height of the mirage is 6 arc min, a size easily perceived by the human eye. This image is not compensated for loss of contrast due to atmospheric scattering.

Fig. 5
Fig. 5

Light rays for a partial duct of length 120 km. The inversion has a strength of 9 °C and a gradient of 0.6°/m, centered on an elevation of 60 m. Observer position and ray angles are the same as for Fig. 3(b). The standard atmosphere has a lapse rate of 0.006°/m.

Fig. 6
Fig. 6

Mirage of the nearest part of Greenland, as seen with the partial duct. The image is different from that of Fig. 4, because the rays intersect the landscape at higher elevations, but the mirage has the same height of 6 arc min. The image is not compensated for loss of contrast.

Fig. 7
Fig. 7

Inversion with no ducting. The inversion takes the form of a uniform temperature gradient of 0.112°/m, going from 0 °C at sea level to 13.44° at an elevation of 120 m. Beyond 120 km the atmosphere reverts to the standard atmosphere with lapse rate 0.006°/m. Ray angles at the observer are 0–4 arc min, in steps of 1 arc min.

Fig. 8
Fig. 8

Rays from Ritur in Iceland to the nearest part of Greenland. The inversion of Region II, which is the same as the inversion in Fig. 5, is flanked by two regions (I and III) of standard atmosphere. The rays at the observer’s eye have elevation angles from -38 to -35 arc min, in steps of 0.5 arc min.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

αλ=f 8π33ns2-12Ns2λ40d Ndx,
ns-1=A1+B/λ2,
αλ=d×σm.
qλ=exp-αλ.
B=Bh1-qλ,
B=B0qλ+Bh1-qλ.

Metrics