Sunstone (medieval)

Iceland spar, possibly the Icelandic medieval sunstone used to locate the sun in the sky when obstructed from view.

The sunstone (Icelandic: sólarsteinn) is a type of mineral attested in several 13th–14th century written sources in Iceland, one of which describes its use to locate the sun in a completely overcast sky. Sunstones are also mentioned in the inventories of several churches and one monastery in 14th–15th century Iceland. A theory exists that the sunstone had polarizing attributes and was used as a navigation instrument by seafarers in the Viking Age.^[1]

Contents 1 Sources 2 Allegorical nature of the medieval texts 3 Sunstones for orientation and navigation? 4 See also 5 References 6 External links

Sources

One medieval source in Iceland, "Rauðúlfs þáttr",^[2][3] mentions the sunstone as a mineral by means of which the sun could be located in an overcast and snowy sky by holding it up and noting where it emitted, reflected or transmitted light (hvar geislaði úr honum).^[4] Sunstones are also mentioned in Hrafns saga Sveinbjarnarsonar (13th century)^[5] and in church and monastic inventories (14th–15th century) without discussing their attributes. The sunstone texts of Hrafns saga Sveinbjarnarsonar were copied to all four versions of the medieval hagiography Guðmundar saga góða.^[6]
The description in "Rauðúlfs þáttr" of the use of the sunstone is as follows:

Thorsteinn Vilhjalmsson translation: The weather was thick and snowy as Sigurður had predicted. Then the king summoned Sigurður and Dagur (Rauðúlfur's sons) to him. The king made people look out and they could nowhere see a clear sky. Then he asked Sigurður to tell where the sun was at that time. He gave a clear assertion. Then the king made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigurður’ s prediction.[7]

In Icelandic: "Veður var þykkt og drífanda sem Sigurður hafði sagt. Þá lét konungur kalla til sín Sigurð og Dag. Síðan lét konungur sjá út og sá hvergi himin skýlausan. Þá bað hann Sigurð segja hvar sól mundi þá komin. Hann kvað glöggt á. Þá lét konungur taka sólarstein og hélt upp og sá hann hvar geislaði úr steininum og markaði svo beint til sem Sigurður hafði sagt".[8]

Allegorical nature of the medieval texts

Two of the original medieval texts on the sunstone are allegorical. Hrafns saga Sveinbjarnarsonar contains a burst of purely allegorical material associated with Hrafn’s slaying. This involves a celestial vision with three highly cosmological knights, recalling the horsemen of the Apocalypse.^[5] It has been suggested^[9] that the horsemen of Hrafns saga contain allegorical allusions to the winter solstice and the four elements as an omen of Hrafn’s death, where the sunstone also appears.
"Rauðúlfs þáttr", a tale of Saint Olav, and the only medieval source mentioning how the sunstone was used, is a thoroughly allegorical work.^[10] A round and rotating house visited by Olav has been interpreted as a model of the cosmos and the human soul,^[11] as well as a prefiguration of the Church.^[12] The intention of the author was to achieve an apotheosis of St. Olav, through placing him in the symbolic seat of Christ.^[10] The house belongs to the genre of "abodes of the sun," which seemed widespread in medieval literature.^[3] St. Olav used the sunstone to confirm the time reckoning skill of his host right after leaving this allegorical house. He held the sunstone up against the snowy and completely overcast sky and noted where light was emitted from it (the Icelandic words used do not make it clear whether the light was reflected by the stone, emitted by it or transmitted through it). It has been suggested^[9][13] that in Rauðúlfs þáttr the sunstone was used as a symbol of the Virgin, following a widespread tradition in which the virgin birth of Christ is compared with glass letting a ray of the sun through.^[14]
The allegories of the above mentioned texts exploit the symbolic value of the sunstone, but the church and monastic inventories, however, show that something called sunstones did exist as physical objects in Iceland.^[15] The presence of the sunstone in "Rauðúlfs þáttr" may be entirely symbolic^[16] but its use is described in sufficient detail to show that the idea of using a stone to find the sun's position in overcast conditions was commonplace.^[9]

Sunstones for orientation and navigation?

Danish archaeologist Thorkild Ramskou posited that the sunstone could have been one of the minerals (cordierite or Iceland spar) that polarize light and by which the azimuth of the sun can be determined amid a partly overcast sky or when the sun is just below the horizon.^[1][17] The principle is used by many animals^[18] and was applied during polar flights before more advanced techniques became available.^[19][20] Ramskou further conjectured that the sunstone could have aided navigation in the open sea in the Viking period. This idea has become very popular,^[21] and despite no extant records of the use of a sunstone for navigation exist in the medieval literature, research as to how a sunstone could be used in nautical navigation is ongoing. Research in 2011 by Ropers et al. ^[22] , 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. The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye. The recovery of an Iceland spar sunstone from the Elizabethan ship Alderney that sank in 1592 suggests that the navigational technology may have persisted after the invention of the magnetic compass. While other scholars argue that a polarizing mineral only gives the horizontal angle of the sun (azimuth), which is only of marginal value when navigating the open sea.^[16]
Of course, if you can identify the solar azimuth, and you have some means to judge the time of day, it becomes easy to determine the direction of north to a fair degree of accuracy. Every boy scout is taught how to do this, so I will not insult the reader's intelligence by quoting a reference. Imagine a clock-face laid flat and oriented so that the solar azimuth passes through the twelve o'clock position, and suppose furthermore that the time is estimated to be three o'clock; then (in the northern hemisphere) the direction exactly halfway between twelve o'clock and three o'clock represents due south. We can only speculate whether the Vikings were familiar with this concept; but it would have been easy enough to estimate the time of day at sea: a simple water-clock or a graduated candle would have met their needs. The reader will readily understand that any bearing, at any time of day, can be easily extrapolated from these data. By "time of day" we would mean the exact proportion of the daylight hours which had elapsed since sunrise. If today's daylight span had consumed exactly four fillings of the water-clock, then tomorrow, after two fillings had been consumed, we could safely assume that the time was exactly mid-day, the sun was due south; and any other bearing could be extrapolated from that.
The next question is, how does one maintain the ship on heading, without taking a fresh sunstone bearing every five minutes? Well, perhaps some of the more cautious Vikings did just that, we don't know! But it seems unnecessary. To make best use of the wind, the set of sails must be trimmed very precisely. If it becomes obvious that the ship is no longer sailing efficiently, either the wind has changed, or the ship has wandered off course. Statistically, the latter is the more likely case. A wise commander would steady the ship and order the navigator to check the sunstone. For additional confirmation, a pennant (or other form of weathercock) could be worn at the masthead. Since a ship never travels as fast as the wind which is blowing it, the pennant will show the ship's bearing relative to wind direction very clearly.
It is understandable that the sunstone would have persisted into medieval ages as a backup navigational system; this would have nothing to do with the stage of development of compasses: it simply reflects the fact that, in any locality where magnetic variation has not yet been quantified (which meant nearly everywhere, at that time), the sunstone will provide more accurate bearings than can be achieved with a compass.
Beyond nautical navigation, a polarizing crystal would have been useful as a sundial, especially at high latitudes with extended hours of twilight, in mountainous areas or in partly overcast conditions. This use would require the polarizing crystal to be used in conjunction with known landmarks; churches and monasteries would have valued such an object as an aid to keep track of the canonical hours.^[9]

See also

• Allegory in the Middle Ages
• Solar compass

References

1. ^ ^{a b} Ramskou, Thorkild. 1967. Solstenen. Skalk. ISBN 91-29-56391-7. 2: 16–17.
2. ^ Turville-Petre, Joan E. (Trans.) (1947). "The story of Rauð and his sons. Payne Memorial Series II. Viking Society for Northern Research. ISBN 0-404-60014-X.
3. ^ ^{a b} Faulkes, Anthony. 1966. "Rauðúlfs þáttr: A study". Studia Islandica 25. Heimspekideild Háskóla Íslands og Bókaútgáfa Menningarsjóðs. Reykjavík. ISSN 0258-3828. 92 pp.
4. ^ Sample, Ian."Crystals may have aided Viking sailors". Guardian (Manchester, UK) p. 8. 7 February 2007. Retrieved December 27, 2010. "Tests aboard a research vessel in the Arctic ocean found that certain crystals can be used to reveal the position of the sun, a trick that would have allowed early explorers to ascertain their position and navigate, even if the sky was obscured by cloud or fog."
5. ^ ^{a b} Helgadóttir, Guðrún P (ed.). 1987. Hrafns Saga Sveinbjarnarsonar. Oxford: Clarendon Press. ISBN 0-19-811162-2. 267 pp.
6. ^ Karlsson, Stefán (ed.).1983. Guðmundar sögur biskups I: Ævi Guðmundar biskups, Guðmundar saga A. Editiones Arnamagnæanæ, Series B (6). København: C.A. Reitzels Forlag. ISBN 87-7421-387-3. 262 pp.
7. ^ Vilhjalmsson, Thorsteinn. 1997. "Time and Travel in Old Norse Society". Disputatio, (II): 89–114.
8. ^ Johnsen, Oscar Albert and Jón Helgason (eds.). 1941. Saga Óláfs konungs hins helga. Den store saga om Olav den hellige. Efter pergamenthandskrift i Kungliga Biblioteket i Stockholm nr. 2 4to med varianter fra andre handskrifter. ("Saga of King Olaf the Holy. The great saga of Olav the Holy. After the parchment manuscript no. 2 4to in the Royal Library in Stockholm with variants from other manuscripts.") Oslo: Norsk Historisk Kjeldeskrifts-Institutt, Vol. II. pp. 670–1
9. ^ ^{a b c d} Einarsson, Árni. 2010. Sólarsteinninn: tæki eða tákn. (Summary in English: Sunstone: fact or fiction). Gripla 21 (1) 281–97 Árni Magnússon Institute. ISSN 1018-5011.
10. ^ ^{a b} Einarsson, Árni. 1997. "Saint Olaf’s dream house. A medieval cosmological allegory". Skáldskaparmál 4: 179–209, Reykjavík: Stafaholt. ISSN 1026-213X
11. ^ Einarsson, Árni. 2001. The symbolic imagery of Hildegard of Bingen as a key to the allegorical Raudulfs thattr in Iceland. Erudiri Sapientia, Studien zum Mittelalter und zu seiner Rezeptionsgeschichte (Studies on the Middle Ages and their reception history); II: 377–400. ISSN 1615-441X
12. ^ Loescher, G. 1981. "Rauðúlfs þáttr". Zeitschrift für deutsches Altertum und Deutsche Literatur (ZfDA) 110: 253-266. ISSN 0044-2518
13. ^ Bragason, Úlfar 1988. "The structure and meaning of Hrafns saga Sveinbjarnarsonar". Scandinavian Studies 60: 267–292. ISSN 0036-5637
14. ^ Breeze, Andrew. 1999. "The Blessed Virgin and the Sunbeam Through Glass". Celtica 23: 19–29. ISSN 0069-1399
15. ^ Foote, Peter G. 1956. "Icelandic sólarsteinn and the Medieval Background". Arv. Nordic Yearbook of Folklore. 12: 26-40.
16. ^ ^{a b} Schnall, Uwe. 1975. Navigation der Wikinger. Nautische Probleme der Wikingerzeit im Spiegel der schriftlichen Quellen. Schr. Deutsch. Schiffahrtsmus. ("Navigation of the Vikings: Nautical Problems of the Viking Age in the Light of the Written Sources. Writings of the German Maritime Museum"). Band 6. Oldenburg and Hamburg: Stalling, p. 196. ISBN 3-7979-1871-2.
17. ^ Ramskou, Thorkild. 1969. Solstenen – Primitiv Navigation i Norden för Kompasset. Köbenhavn: Rhodos. 95 pp.
18. ^ Horváth, Gábor and Dezsö Varjú. 2004. Polarized Light in Animal Vision: Polarization Patterns in Nature. Springer. pp. 447. ISBN 3-540-40457-0.
19. ^ Moody, Alton B. 1950. "The Pfund Sky Compass"; (via page archive at WebCite). Navigation. 2 (7): 234–239. ISSN 0028-1522.
20. ^ Rogers, Francis M. 1971. "Precision Astrolabe Portuguese Navigators and Transoceanic Navigation - Kollsmann Sky Compass". Academia Internacional da Cultura Portugeusa (Lisbon, Portugal) pp. 288-291. Retrieved December 29, 2010.
21. ^ Hegedüs, Ramón, Åkesson, Susanne; Wehner, Rüdiger and Horváth, Gábor. 2007. "Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggy and cloudy skies". Proc. R. Soc. A 463 (2080): 1081–1095. doi:10.1098/rspa.2007.1811. ISSN 0962-8452.
22. ^ Ropars, G. et al., 2011. A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science. Available at: http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369.abstract [Accessed December 5, 2011].

External links

• The Fabled Viking Sunstone
• The Viking Sunstone Is the legend of the Sun-Stone true ?
  
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