scholarly journals A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight

2011 ◽  
Vol 468 (2139) ◽  
pp. 671-684 ◽  
Author(s):  
Guy Ropars ◽  
Gabriel Gorre ◽  
Albert Le Floch ◽  
Jay Enoch ◽  
Vasudevan Lakshminarayanan
Keyword(s):  
Degree Of Polarization ◽  
The Sun ◽  
Calcite Crystal ◽  
Birefringent Crystal ◽  
Northern Latitudes ◽  
Polarization Of Light ◽  
Iceland Spar

Viking navigation from Norway to America in the northern latitudes remains a mystery for physicists, historians and archaeologists. Polarimetric methods using absorbing dichroic crystals as polarizers to detect a hidden Sun direction using the polarized skylight have led to controversies. Indeed, these techniques may lack in sensitivity, especially when the degree of polarization is low. Here, we demonstrate theoretically and experimentally that using the transparent common Iceland spar as a depolarizer, the Vikings could have performed a precise navigation under different conditions. Indeed, when simply rotated, such a birefringent crystal can completely depolarize, at the so-called isotropy point, any partially polarized state of light, allowing us to guess the direction of the Sun. By equalizing the intensities of the ordinary and extraordinary beams at the isotropy point, we show that the Sun direction can be determined easily, thanks to a simple sensitive differential two-image observation. A precision of a few degrees could be reached even under dark crepuscular conditions. The exciting recent discovery of such an Iceland spar in the Alderney Elizabethan ship that sank two centuries before the introduction of the polarization of light in optics may support the use of the calcite crystal for navigation purposes.

scholarly journals The sixteenth century Alderney crystal: a calcite as an efficient reference optical compass?

2013 ◽  
Vol 469 (2153) ◽  
pp. 20120651 ◽  
Author(s):  
Albert Le Floch ◽  
Guy Ropars ◽  
Jacques Lucas ◽  
Steve Wright ◽  
Trevor Davenport ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Sixteenth Century ◽  
Crucial Role ◽  
Sea Water ◽  
The Sun ◽  
Calcite Crystal ◽  
Sun Compass ◽  
Sand Abrasion ◽  
Iceland Spar

The crystal recently discovered in the 1592 sunken Elizabethan ship is shown to be an Iceland spar. We report that two main phenomena, with opposite effects, explain the good conservation and the evolution of this relatively fragile calcite crystal. We demonstrate that the Ca 2+ –Mg 2+ ion exchanges in such a crystal immersed in sea water play a crucial role by limiting the solubility, strengthening the mechanical properties of the calcite, while the sand abrasion alters the crystal by inducing roughness of its surface. Although both phenomena have reduced the transparency of the Alderney calcite crystal, we demonstrate that Alderney-like crystals could really have been used as an accurate optical sun compass as an aid to ancient navigation, when the Sun was hidden by clouds or below the horizon. To avoid the possibility of large magnetic errors, not understood before 1600, an optical compass could have helped in providing the sailors with an absolute reference. An Alderney-like crystal permits the observer to follow the azimuth of the Sun, far below the horizon, with an accuracy as great as ±1 ° . The evolution of the Alderney crystal lends hope for identifying other calcite crystals in Viking shipwrecks, burials or settlements.

scholarly journals On the variable intensity of ter­restrial magnetism, and the influence of the aurora borealis upon it

1837 ◽  
Vol 3 ◽  
pp. 37-38
Keyword(s):  
Magnetic Force ◽  
The Sun ◽  
South Pole ◽  
Variable Intensity ◽  
Aurora Borealis ◽  
The North ◽  
The Earth ◽  
Northern Latitudes ◽  
Snow Storms ◽  
Magnetic Needle

The author gives the results of a series of observations on the vibrations of the magnetic needle, which he undertook last summer, for the purpose of ascertaining whether the intensity of its directive force is affected by the changes in the earth’s distance from the sun, or by its declination with respect to the plane of its equator. He observed that the magnetic intensity is subject to frequent variations, which are sometimes sudden, and of short duration. These anomalies he has been unable to refer to any obvious cause, except when they were accompanied by the appearance of the aurora borealis, which evidently affected the needle on many occasions. He also thinks that the vibrations of the needle became less rapid with a moist atmosphere, and more so when it was very dry. Changes of the wind and snow storms appeared also to be attended with fluc­tuations in the intensity of the magnetism. He endeavoured to ascertain whether there existed any decided and constant difference in the directive force of each pole; conceiving that, on the hypothesis of a central magnetic force, the north pole of the magnet would, in these northern latitudes, be acted upon with much greater energy than the south pole. From his observing that the relative intensity of the two poles is not always the same, he infers the probability of the earth’s magnetism being derived from the agency of electric currents existing under its surface as well as above it, and that the rapid fluctuations in its intensity are owing to meteorological changes. The author is led to conclude that the aurora borealis is an elec­trical phenomenon, and that it usually moves during the night nearly from north to south, and in an opposite direction during the day ; that it is of the nature of positive electricity; and that its elevation above the earth is much greater than a thousand, and perhaps thou­sands of miles.

The Polarization of Thermal 'Solar Noise' and a Determination of the Sun's General Magnetic Field

1950 ◽  
Vol 3 (2) ◽  
pp. 265 ◽  
Author(s):  
SF Smerd
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Observational Evidence ◽  
Degree Of Polarization ◽  
The Sun ◽  
Maximum Phase ◽  
General Magnetic Field ◽  
Upper Limit ◽  
Surface Field

The equation of transfer of radiation and the magneto-ionic theory are used to derive expressions for the degree of polarization of thermal " solar noise " due to a general magnetic field of the sun. In particular, the net polarization of 600 Mc/s. (50 cm.) radiation corresponding to the maximum phase of the eclipse of November 1, 1948, as seen from Melbourne, Victoria, is evaluated theoretically and compared with observational evidence. This leads to an upper limit of 11 gauss for the surface field- strength at the solar poles at the time of observation.

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

2007 ◽  
Vol 463 (2080) ◽  
pp. 1081-1095 ◽  
Author(s):  
Ramón Hegedüs ◽  
Susanne Åkesson ◽  
Rüdiger Wehner ◽  
Gábor Horváth
Keyword(s):  
Linear Polarization ◽  
The Sun ◽  
Direct Sunlight ◽  
Birefringent Crystal ◽  
Clear Sky ◽  
Open Sea ◽  
Skylight Polarization ◽  
Imaging Polarimetry

In sunshine, the Vikings navigated on the open sea using sundials. According to a widespread hypothesis, when the Sun was occluded by fog or clouds the Vikings might have navigated by skylight polarization detected with an enigmatic birefringent crystal (sunstone). There are two atmospheric optical prerequisites for this alleged polarimetric Viking navigation under foggy/cloudy skies: (1) the degree of linear polarization p of skylight should be high enough and (2) at a given Sun position, the pattern of the angle of polarization α of the foggy/cloudy sky should be similar to that of the clear sky. Until now, these prerequisites have not been investigated. Using full-sky imaging polarimetry, we measured the p - and α -patterns of Arctic foggy and cloudy skies when the Sun was invisible. These patterns were compared with the polarization patterns of clear Arctic skies. We show here that although prerequisite (2) is always fulfilled under both foggy and cloudy conditions, if the fog layer is illuminated by direct sunlight, prerequisite (1) is usually satisfied only for cloudy skies. In sunlit fog, the Vikings could have navigated by polarization only, if p of light from the foggy sky was sufficiently high.

scholarly journals On the trail of Vikings with polarized skylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers

2011 ◽  
Vol 366 (1565) ◽  
pp. 772-782 ◽  
Author(s):  
Gábor Horváth ◽  
András Barta ◽  
István Pomozi ◽  
Bence Suhai ◽  
Ramón Hegedüs ◽  
...  
Keyword(s):  
North Atlantic ◽  
Laboratory Experiments ◽  
High Arctic ◽  
Exact Nature ◽  
The Sun ◽  
Birefringent Crystal ◽  
The North ◽  
Open Sea ◽  
Skylight Polarization ◽  
The North Atlantic

Between AD 900 and AD 1200 Vikings, being able to navigate skillfully across the open sea, were the dominant seafarers of the North Atlantic. When the Sun was shining, geographical north could be determined with a special sundial. However, how the Vikings could have navigated in cloudy or foggy situations, when the Sun's disc was unusable, is still not fully known. A hypothesis was formulated in 1967, which suggested that under foggy or cloudy conditions, Vikings might have been able to determine the azimuth direction of the Sun with the help of skylight polarization, just like some insects. This hypothesis has been widely accepted and is regularly cited by researchers, even though an experimental basis, so far, has not been forthcoming. According to this theory, the Vikings could have determined the direction of the skylight polarization with the help of an enigmatic birefringent crystal, functioning as a linearly polarizing filter. Such a crystal is referred to as ‘sunstone’ in one of the Viking's sagas, but its exact nature is unknown. Although accepted by many, the hypothesis of polarimetric navigation by Vikings also has numerous sceptics. In this paper, we summarize the results of our own celestial polarization measurements and psychophysical laboratory experiments, in which we studied the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic.

scholarly journals Polarization of white-light solar corona and sky polarization effect during total solar eclipse on March 29, 2006

2019 ◽  
pp. 83-87 ◽  
Author(s):  
V. Merzlyakov ◽  
Ts. Tsvetkov ◽  
L. Starkova ◽  
R. Miteva
Keyword(s):  
Solar Corona ◽  
Solar Eclipse ◽  
White Light ◽  
Linear Dependence ◽  
Polarization Effect ◽  
Thomson Scattering ◽  
Total Solar Eclipse ◽  
Degree Of Polarization ◽  
The Sun ◽  
Eclipse Observations

Ground-based total solar eclipse observations are still the key method for coronal investigations. The question about its white-light degree of polarization remains unanswered. There are hypotheses claiming that the degree of polarization in certain regions of the corona may be higher than the maximal theoretically predicted value determined by Thomson scattering. We present polarization of the white-light solar corona observations obtained by three different teams during the March 29, 2006 solar total eclipse. We give an interpretation on how the polarization of the sky impacts brightness of the polarized solar corona, depending on the landscape during the totality. Moreover, it is shown that the singular polarization points of the corona are in linear dependence with the height of the Sun above the horizon.

scholarly journals Optical polarimetry and photometry of young sun-like star LO Peg

2010 ◽  
Vol 6 (S273) ◽  
pp. 455-459
Author(s):  
J. C. Pandey ◽  
B. J. Medhi ◽  
R. Sagar
Keyword(s):  
Radiation Field ◽  
Position Angle ◽  
Degree Of Polarization ◽  
Circumstellar Envelope ◽  
The Sun ◽  
Photometric Study ◽  
V Band ◽  
Stellar Radiation ◽  
Photometric Observations

AbstractWe have carried out the B,V and R-band polarimetric and V-band photometric study of the star LO Peg. Our analysis reveal that LO Peg is highly polarized among the sun-like stars. The degree of polarization and polarization position angle are found to be rotationally modulated. The levels of polarization observed in LO Peg could be the result of scattering of an anisotropic stellar radiation field by an optically thin circumstellar envelope or scattering of the stellar radiation by prominence-like structures. The long term photometric observations of LO Peg indicate three independent groups of spots are present on the surface of LO Peg.

scholarly journals On the laws which regular the polarization of light by reflection from transparent bodies. By David Brewster, LL. D. F. R. S. Edin. and F. S. A. Edin. In a letter addressed to the Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S

1833 ◽  
Vol 2 ◽  
pp. 14-15 ◽  
Keyword(s):  
The Right ◽  
Polarization Of Light ◽  
Iceland Spar

Though Huygens, who first explained the laws that regulate the extraordinary refraction of light at a surface of Iceland spar, discovered that light thus separated has properties different from common light; and though Newton observed that light thus modified has permanent properties, with reference to the plane in which it has been refracted, and expressed this peculiarity by saying that these rays have sides according to which its subsequent refractions are regulated;—it was Malus who gave to this modification the name of polarization, a term by which he could conveniently express the various affections which such light undergoes by refraction or reflection in different directions; and could thereby most distinctly describe the various phenomena relating to his important discovery, that light may also by reflection acquire the same properties that are given by refraction through Iceland spar and other doubly refracting crystals. Malus ascertained, that when light is incident on the surface of water at a certain angle, that portion of it which is reflected is completely polarized; and that when light is incident on the surface of other media, the angle at which complete polarization of the reflected portion takes place will be different, being greater when the reflecting substance has a higher refractive. But Malus did not succeed in detecting the rule by which the requisite angles of incidence for different bodies could be inferred from their refractive powers.

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