Light and polarizationnotes

To examine this further, consider the transverse waves in the ropes shown in Figure 2.3.13. The oscillations in one rope are in a vertical plane and are said to be vertically polarized. Those in the other rope are in a horizontal plane and are horizontally polarized. If a vertical slit is placed on the first rope, the waves pass through. However, a vertical slit blocks the horizontally polarized waves. For EM waves, the direction of the electric field vector E is analogous to the disturbances on the ropes (Figure 2.3.14).

Polarizedandunpolarizedlight

Another interesting phenomenon associated with polarized light is the ability of some minerals and other crystals to split an unpolarized beam of light into two polarized beams (Figure 2.3.22). Such crystals are said to be birefringent.

In flat screen LCD televisions, there is a large light at the back of the TV. The light travels to the front screen through millions of tiny units called pixels (picture elements). One of these is shown in Figure 2.3.19 (a) and (b). Each unit has three cells, with red, blue, or green filters, each controlled independently. When the voltage across a liquid crystal is switched off, the liquid crystal passes the light through the particular filter. One can vary the picture contrast by varying the strength of the voltage applied to the liquid crystal.

“James Bradley’s discovery of stellar aberration, published 1729, eventually gave direct evidence excluding the possibility of all forms of geocentrism including Tycho’s.”

Light and polarizationdifference

As mentioned in my above graphic, please note that the lengths A and B (representing two of the most well-known, empirically-verifiable measurements in astronomy) are perfectly consistent, proportionally speaking. I recommend you verify this for yourself with a simple ruler that length B is 1.25 X larger than length A (since 50.3” is 1.25 X larger than 40”).

Watch the first 6 minutes of the video below to see a practical overview of plane polarized light, using crossed polarizers, and how a third polarizer (which is how many minerals act) can be used to increase light output from crossed polarizers.

Each of the separated rays has a specific polarization. One behaves normally and is called the ordinary ray (o or ω), whereas the other does not obey Snell’s law and is called the extraordinary ray (e or ε). Birefringent crystals can be used to produce polarized beams from unpolarized light. Some birefringent materials preferentially absorb one of the polarizations. These materials are called dichroic and can produce polarization by this preferential absorption. This is fundamentally how polarizing filters and other polarizers work. We will use the property of birefringence to help us identify and distinguish minerals in thin section!

Only the component of the EM wave parallel to the axis of a filter is passed. Let us call the angle between the direction of polarization and the axis of a filter θ. If the electric field has an amplitude E, then the transmitted part of the wave has an amplitude E cos θ (see Figure 2.3.18). Since the intensity of a wave is proportional to its amplitude squared, the intensity I of the transmitted wave is related to the incident wave by I = I0 cos2 θ, where I0 is the intensity of the polarized wave before passing through the filter.

Analytical Methods in Geosciences Copyright © by Elizabeth Johnson and Juhong Christie Liu is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

Polarizers are composed of long molecules aligned in one direction. Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 2.3.13).

Keeping in mind that these commensurate values rely on the core principles of the TYCHOS model (what with Earth’s annual 14,036-km-motion & the trochoidal path of earthly observers), the odds for all this to be entirely coincidental are, objectively speaking, beyond rational consideration.

Figure 2.3.16 illustrates how the component of the electric field parallel to the long molecules is absorbed. An electromagnetic wave is composed of oscillating electric and magnetic fields. The electric field is strong compared with the magnetic field and is more effective in exerting force on charges in the molecules. The most affected charged particles are the electrons in the molecules, since electron masses are small. If the electron is forced to oscillate, it can absorb energy from the EM wave. This reduces the fields in the wave and, hence, reduces its intensity. In long molecules, electrons can more easily oscillate parallel to the molecule than in the perpendicular direction. The electrons are bound to the molecule and are more restricted in their movement perpendicular to the molecule. Thus, the electrons can absorb EM waves that have a component of their electric field parallel to the molecule. The electrons are much less responsive to electric fields perpendicular to the molecule and will allow those fields to pass. Thus the axis of the polarizing filter is perpendicular to the length of the molecule.

Ellipticalpolarization

I will now illustrate exactly how — under the TYCHOS model — our North star Polaris will in fact reach its maximum elongation (from an earthly observer) over a 9-month (rather than a 6-month) period and why Polaris is observed to travel annually around a 40”-wide ellipse.

S-polarization vs ppolarization

“It is important to notice that the early attempts were at measuring what today would be called absolute parallax, rather than relative parallax, which is the parallax of a nearer star with respect to that of a distant star”.

Astronomer Royal James Bradley’s Aberration of starlight is widely celebrated as the definitive proof of Earth’s motion around the Sun as it supposedly hurtles at supersonic speeds along a 300 Mkm-wide orbit. For those who might (understandably) never have heard of the formidably contrived “Aberration of light” theory, here follow some basic descriptions of this arcane astronomical concept.

The almost comical “stellar aberration” theory which Bradley concocted (in his urge to justify otherwise inexplicable observations) has to be among the most contorted attempts at rescuing the doomed Copernican model. In hindsight, it is quite ironic that Bradley’s painstaking efforts very nearly ended up imploding the Copernican theory from within, since his (otherwise quite valid & correct) observations were in stark contradiction with the Copernically expected stellar motions.

Glass and plastic become optically active when stressed; the greater the stress, the greater the effect. Optical stress analysis on complicated shapes can be performed by making plastic models of them and observing them through crossed filters, as seen in Figure 2.3.21. It is apparent that the effect depends on wavelength as well as stress. The wavelength dependence is sometimes also used for artistic purposes.

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass. Polaroids have this ability because of a wave characteristic of light called polarization. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light.

Light and polarizationin physics

Many crystals and solutions rotate the plane of polarization of light passing through them. Such substances are said to be optically active. Examples include sugar water, insulin, and collagen (see Figure 2.3.20). In addition to depending on the type of substance, the amount and direction of rotation depends on a number of factors. Among these is the concentration of the substance, the distance the light travels through it, and the wavelength of light. Optical activity is due to the asymmetric shape of molecules in the substance, such as being helical. Measurements of the rotation of polarized light passing through substances can thus be used to measure concentrations, a standard technique for sugars. It can also give information on the shapes of molecules, such as proteins, and factors that affect their shapes, such as temperature and pH.

That’s right! Bradley and his peers found that, to their amazement, the maximum annual elongation of a circumpolar star from an earthly observer does not occur over the expected six-month time period but will, in fact, occur three months later. i.e.; nine months after the start of a year-long observation.

While you are undoubtedly aware of liquid crystal displays (LCDs) found in watches, calculators, computer screens, cellphones, flat screen televisions, and other myriad places, you may not be aware that they are based on polarization. Liquid crystals are so named because their molecules can be aligned even though they are in a liquid. Liquid crystals have the property that they can rotate the polarization of light passing through them by 90 degrees. Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure 2.3.19. It is possible to manipulate this characteristic quickly and in small well-defined regions to create the contrast patterns we see in so many LCD devices.

Polarizationoflightnotes PDF

Electromagnetic waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation and perpendicular to each other.

The Sun and many other light sources produce waves in which E (and B, though it is not shown) are not preferentially oriented – they exist in every direction perpendicular to the direction of propagation (see Figure 2.3.11). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization.

—p. 222, The Historical Search for Stellar Parallax (Continued)　by J. D. Fernie, from Journal of the Royal Astronomical Society of Canada, Vol. 69, pp.222-239

Difference betweenlight and polarization

In contrast, light that is plane polarized (also called linearly polarized) has E oriented in one specific direction in space (Figure 2.3.12).  The polarization direction is defined by the orientation of E (as opposed to B).

“James Bradley, (born March 1693, Sherborne, Gloucestershire, Eng.—died July 13, 1762, Chalford, Gloucestershire), English astronomer who in 1728 announced his discovery of the aberration of starlight, an apparent slight change in the positions of stars caused by the yearly motion of the Earth. That finding provided the first direct evidence for the revolution of the Earth around the Sun.”

“The aberration of starlight was discovered in 1727 by the astronomer James Bradley while he was searching for evidence of stellar parallax, which in principle ought to be observable if the Copernican theory of the solar system is correct. He succeeded in detecting an annual variation in the apparent positions of stars, but the variation was not consistent with parallax. The observed displacement was greatest for stars in the direction perpendicular to the orbital plane of the Earth, and most puzzling was the fact that the displacement was exactly three months (i.e., 90 degrees) out of phase with the effect that would result from parallax due to the annual change in the Earth’s position in orbit around the Sun.”

Figure 2.3.17 shows the effect of two polarizing filters on originally unpolarized light. The first filter polarizes the light along its axis. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes are perpendicular, no light is passed by the second.

“For instance Polaris, the pole star, seemed to travel annually around an ellipse whose width was 40”, 40 seconds of arc. […] However, the shifts in position did not occur at the times they were expected. The greatest shift of Polaris in any given direction [occurred] not when the Earth’s was at the opposite end of its orbit, as it should have been, but 3 months later. For instance, in the drawing above, the apparent position of Polaris should have been shifted the furthest in the direction of ‘December’ when Earth was in its ‘June’ position, which is far as it can go in the opposite direction. Instead, it happened in September, when the Earth had moved 90° from its position in June.”

Polarizing filters have a polarization axis that acts as a slit. This slit passes electromagnetic waves (often visible light) that have an electric field parallel to the axis. This is accomplished with long molecules aligned perpendicular to the axis as shown in Figure 2.3.15.

Keep in mind the above quote by J.D Fernie, as we shall soon get to the question of relative stellar parallax and its geoptical implications, which, as I shall thoroughly demonstrate, can only find a rational explanation within the TYCHOS model.

The below excerpt of another article neatly sums up Bradley’s puzzling observations, which had astronomers scratching their heads. Why does a star’s maximum elongation occurs in a nine month period, rather than (as Copernican astronomers would expect) a six month period? Furthermore, why would a circumpolar star such as Polaris be observed to travel around an ellipse of 40 seconds of arc, while stars level with Earth’s equatorial plane are all seen precessing annually by about 50.3 seconds of arc?