Polarization Polarization SundialsSundials

Montgomery College PlanetariumMontgomery College Planetarium

by Dr. Harold Williamsby Dr. Harold Williams

http://montgomerycollege.edu/Departments/planet/http://montgomerycollege.edu/Departments/planet/ http://montgomerycollege.edu/Departments/planet/planet/polarsun.hthttp://montgomerycollege.edu/Departments/planet/planet/polarsun.htmlml

All SundialsAll Sundials All sundials tell time by the position of the sun in All sundials tell time by the position of the sun in

the sky. Mostly they tell local apparent sun time.the sky. Mostly they tell local apparent sun time. At sunrise the sun is just coming up on the At sunrise the sun is just coming up on the

horizon.horizon. At midday, noon, the sun is crossing the At midday, noon, the sun is crossing the

meridian, the line that runs from north to south meridian, the line that runs from north to south through the zeinth, (the point over head).through the zeinth, (the point over head).

At sunset the sun is just going down on the At sunset the sun is just going down on the horizon.horizon.

Most SundialsMost Sundials

Most sundials work by casting Most sundials work by casting shadows with a “gnome,” shadows with a “gnome,” shadow caster.shadow caster.

The shadow is projected on a The shadow is projected on a surface that is a dial face surface that is a dial face telling you the time.telling you the time.

Polarization SundialsPolarization Sundials

Determine the position of the sun by Determine the position of the sun by measuring the polarization of the sky.measuring the polarization of the sky.

The polarization of scattered sunlight in The polarization of scattered sunlight in our atmosphere tells us where the sun is our atmosphere tells us where the sun is even when the sun has no shadows even when the sun has no shadows because it is covered by a cloud or you because it is covered by a cloud or you are shadowed by a building. are shadowed by a building.

But people can not see polarization so But people can not see polarization so how do you measure it in the sky! how do you measure it in the sky!

What is Polarization and how can What is Polarization and how can you see it to measure it?you see it to measure it?

Most light sources produce unpolarized light, or Most light sources produce unpolarized light, or light with both polarization states mixed equally.light with both polarization states mixed equally.

So you must have an analyzer to see So you must have an analyzer to see polarization, unless you are an bee or some polarization, unless you are an bee or some other insects or octopus, squid, cuttlefish, or other insects or octopus, squid, cuttlefish, or mantis shrimp, but evidently not pigeons then mantis shrimp, but evidently not pigeons then you have an analyzer in your eye already you have an analyzer in your eye already evolved. evolved.

Haidinger'sHaidinger's brush brush, some people can be trained , some people can be trained to see polarization weekly!to see polarization weekly!

Visible LightVisible Light

Visible light is electromagnetic radiation of Visible light is electromagnetic radiation of a limited frequency and wavelength.a limited frequency and wavelength.

All electromagnetic radiation: radio waves, All electromagnetic radiation: radio waves, micro waves, infrared, visible light, micro waves, infrared, visible light, ultraviolet, x-ray, through gamma rays, has ultraviolet, x-ray, through gamma rays, has twotwo polarization states! polarization states!

http://en.wikipedia.org/wiki/Polarizationhttp://en.wikipedia.org/wiki/Polarization

Linear Circular Elliptical

Polarization is perpendicular to the plane Polarization is perpendicular to the plane containing the sky point, the sun, and the containing the sky point, the sun, and the

observer.observer.

Maximum polarization in the sky occur at a point Maximum polarization in the sky occur at a point 90 degrees from the sun in the plane containing 90 degrees from the sun in the plane containing

the sun observer and zenith.the sun observer and zenith.

The plane containing the sun, observer, and the celestial The plane containing the sun, observer, and the celestial pole rotate counter clockwise uniformly about the celestial pole rotate counter clockwise uniformly about the celestial

pole making one turn in a local apparent solar day. The pole making one turn in a local apparent solar day. The major polarization vector is always 90 degrees to the plane.major polarization vector is always 90 degrees to the plane.

So it should be possible to make a gnomeless, no shadow caster,sundial using the polarization pattern in the sky. This should be easiest if you use the polarization pattern around the celestial pole since it rotates uniformly. Sort of like an equatorial gnomned sundial has uniform dial with hours 15 degrees apart since 15 degrees/hour x 24 hours/revolution=360 degrees/revolution.

Equatorial Sundial with Gnome Equatorial Sundial with Gnome pointing toward the polepointing toward the pole

Equatorial Sundials across the Equatorial Sundials across the planetplanet

Equatorial Sundial SummerEquatorial Sundial Summer

Equatorial Sundial WinterEquatorial Sundial Winter

History of PolarizationHistory of Polarization Etienne-Louis Malus (1775-1812) Etienne-Louis Malus (1775-1812)

Discovered polarization in 1808Discovered polarization in 1808 François Arago (1786-1853) discovered François Arago (1786-1853) discovered

polarization of the sky in 1809polarization of the sky in 1809 Babinet, Brewster, and others Babinet, Brewster, and others

extended sky polarization extended sky polarization Charles Wheatstone (1802-1875) Charles Wheatstone (1802-1875)

actual built a polarization sundial in actual built a polarization sundial in 18481848

EventuallyEventually John William Strutt alias John William Strutt alias Lord Lord Rayleigh (1842-1919) in 1870s Rayleigh Rayleigh (1842-1919) in 1870s Rayleigh scattering in the sky scattering in the sky

Wheatstone’s polarizing sundial Wheatstone’s polarizing sundial at the Science Museum, Londonat the Science Museum, London

Folding-pattern polarization Folding-pattern polarization sundial designed for demo by sundial designed for demo by

Charles WheatstoneCharles Wheatstone

So how come polarization So how come polarization sundials are not commonsundials are not common

Improvement in technology has made Improvement in technology has made polarization sundials much easier and cheaper to polarization sundials much easier and cheaper to make now than in Wheatstone's time when Nicol make now than in Wheatstone's time when Nicol prism (calcite prism where one polarization prism (calcite prism where one polarization encountered black paint) were used.  encountered black paint) were used. 

Edwin Land discovers how to embed iodosulphate Edwin Land discovers how to embed iodosulphate of quinine (herapathite) microscopic crystals, of quinine (herapathite) microscopic crystals, which are dichroic crystals which are both which are dichroic crystals which are both birefringent and colored, aligning them by birefringent and colored, aligning them by stretching them in polyvinyl alcohol films stretching them in polyvinyl alcohol films between sheets of cellulose acetate-butyrate between sheets of cellulose acetate-butyrate (CAB)HN32 linear polarizer, Polaroid.(CAB)HN32 linear polarizer, Polaroid.

All references in the Literature are in All references in the Literature are in obscure English Journals. obscure English Journals.

Of course why build sundial at Of course why build sundial at all when we have ephemeral all when we have ephemeral

watches and clockswatches and clocksTo teach physical principles about the To teach physical principles about the

movement of the sun and the earth, the movement of the sun and the earth, the day and the seasons, in the case of day and the seasons, in the case of shadow sundials.shadow sundials.

Polarization sundials besides teaching Polarization sundials besides teaching about daily motion can be used to about daily motion can be used to explain spooky facts about polarization.explain spooky facts about polarization.

Spooky PolarizationSpooky Polarization

Regeneration of polarization by putting the third Regeneration of polarization by putting the third Polaroid between the two crossed Polaroids.Polaroid between the two crossed Polaroids.

Quantum mechanics in action Quantum mechanics in action 2. The 2. The polarization of photonspolarization of photons pages 4-7 in the 4th pages 4-7 in the 4th edition of edition of Quantum MechanicsQuantum Mechanics by P.A.M. Dirac. by P.A.M. Dirac. This is in the first chapter on The Principle of This is in the first chapter on The Principle of Superpositon after Superpositon after 1. The need for a quantum 1. The need for a quantum theorytheory section. Polarization is a true quantum section. Polarization is a true quantum mechanical effect! In the limit of h goes zero mechanical effect! In the limit of h goes zero there is no polarization.there is no polarization.

Novelty factor of making a Novelty factor of making a simple instrument to do sciencesimple instrument to do science

This sundial works when it is in the shadows This sundial works when it is in the shadows since it does not use shadows. So the sun since it does not use shadows. So the sun behind a cloud is no problem. Works in behind a cloud is no problem. Works in courtyards, too, with a patch of blue sky courtyards, too, with a patch of blue sky available.available.

The sun being down is also no problem for an The sun being down is also no problem for an hour before sunrise and an hour after sunset.hour before sunrise and an hour after sunset.

When won’t it work? White clouds depolarized When won’t it work? White clouds depolarized sunlight. So you do need a patch of blue in the sunlight. So you do need a patch of blue in the north for the simplest type of polarization sundial north for the simplest type of polarization sundial to work. to work.

An astro-compass dating from An astro-compass dating from World War IIWorld War II

Half-Shade AnalyzerHalf-Shade Analyzer

Holder for Polaroid and ScaleHolder for Polaroid and Scale

AssemblyAssembly

Putting it togetherPutting it together

Reference ListReference List David Colchester, “A Polarized Skylight Sundial,” David Colchester, “A Polarized Skylight Sundial,”

Bulletin of the British Sundial Society, Bulletin of the British Sundial Society, 96.396.3, pp. , pp. 1315 (1996)1315 (1996)

Allan A. Mills, “The Sellotape Sundial,” Bulletin of Allan A. Mills, “The Sellotape Sundial,” Bulletin of the British Sundial Society, the British Sundial Society, 98.198.1, pp. 3-9 (1998), pp. 3-9 (1998)

Allan A. Mills, “Polarization of Light from the Sky, Allan A. Mills, “Polarization of Light from the Sky, and its application to timetelling and and its application to timetelling and Navigation,” Bulletin of the Scientific Instrument Navigation,” Bulletin of the Scientific Instrument Society, No. Society, No. 3333, pp. 8-14 (1992), pp. 8-14 (1992)

A.H. Pfund, “A Polaroid Half-Shade Analyzer,” A.H. Pfund, “A Polaroid Half-Shade Analyzer,” Journal of the Optical Society of America, Journal of the Optical Society of America, 2626, p. , p. 453 (1936)453 (1936)