Question Does emitted-light have different properties from reflected light?

Jan 25, 2020
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Does emitted-light have different properties from reflected light, and it is for this reason that we see the stars twinkle in the night sky while the planets do not? Note: I know the explanation that attributes the phenomenon to their variation in distance from Earth.
 
Aug 31, 2020
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This is a very important question and has deep implications. If you would like to read about a new theory of the reflection of light, you might like to read this thread. The question of why stars twinkle is as you suggest, due to the huge distances that the light travels and the refraction that light undergoes.
 
Jan 25, 2020
22
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535
This is a very important question and has deep implications. If you would like to read about a new theory of the reflection of light, you might like to read this thread. The question of why stars twinkle is as you suggest, due to the huge distances that the light travels and the refraction that light undergoes.
I think that the stars' light does not appear to twinkle for an onlooker from outer space: their twinkling is correlative with Earth's atmosphere, and, thus, the huge distance their light travels is not, in my opinion, a considered factor. I mean that the refraction the stars' light undergoes occures in the layers of our planets atmosphere, and, as this this refraction does not occure with light refracted by the planets and the Moon as well, it should indicate that there is diference in properties between refleted laight and emitted light. One of these diferences may be that refleted light travels in straight lines, not as a wave.
 
Aug 31, 2020
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The fact is the nearest star to earth is Alpha Centsuri which is approx 40 x 10^12 km distant while the moon is only 2.5 x 10^5 km distant, similarly the sun is 150 x 10^ 6 km distant. There is no comparison between these distances. Yes the earth's atmosphere might be the major cause for the twinkling of stars. But light, of a certain frequency, energy and wavelength is the same whether emitted or reflected.
 
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Jan 25, 2020
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A star 4 light-years from Earth, like Alpha Centauri, should twinkle in a different way from the farthest star visible to the naked eye, if it is a matter of distance.
 
Aug 31, 2020
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It all seems to come down to the earth's atmosphere. Astronauts on the space station see stars shining steadily. Stars seen from the space station do not twinkle.
 
Jan 25, 2020
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You wrote: "But light, of a certain frequency, energy and wavelength is the same whether emitted or reflected." I ask: is this proved mathematically or experimentally?
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Aug 31, 2020
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Light that is reflected is polarized light. That's the difference.
Partially polarised would be more accurate. This is in some part due to the nature of the material it is reflecting off having birefringent properties than anything else. Birefringence is when light falling on the material is dispersed or split into its individual colours. The degree of polarization depends on the angle of incidence and the index of refraction of the reflecting material.

The OP asks whether reflected light; light reflected from the moon and the planets is different from light from stars that is emitted and if this is the reason that stars twinkle. Obviously if reflection is the topic it is a longer discussion. For instance, if light reflects of metal surfaces it does not undergo polarisation and so on.
 
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Feb 19, 2020
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If the question is addressed to me, I have no expertise on that. But it would seem logical that polarized light in would be polarized out.
 
Jan 27, 2020
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When a star’s light pierces our atmosphere, each single stream of starlight is refracted – caused to change direction, slightly – by the various temperature gradients, density layers and turbulence in the Earth’s atmosphere. You might think of it as the star light traveling a zig-zag path to our eyes, instead of the straight path the light would travel if Earth didn’t have an atmosphere.

Stellar scintillation* is described as the effect produced by the scattering of light from refractive index variations in the Earth’s atmosphere. The refractive index variations cause changes in the phase of the light and these, in turn, lead to intensity variations. The intensity may vary spatially and temporally forming what is often referred to as a shadow pattern at the Earth’s surface. The twinkling of stars arises from the motion of this shadow pattern across the eye as well as from fluctuations in the pattern itself. Since our eyes are rather slow detectors, the twinkling is a time-integrated observation of the complete scintillation process.

The apparent position of the star is different from the actual position. As the atmosphere bends the starlight, the star will appear slightly higher when seen from the near the horizon. This position of star keeps on changing with the changing atmosphere because of its dynamic physical conditions.

Why-do-stars-twinkle-.png

Refraction in physics means a change in the direction of a wave (Lightwave, sound wave, and water waves) when it passes from one medium to another. Therefore when the light from the star undergoes refraction before entering the earth’s atmosphere because of change in the medium. As a result the refractive index changes gradually.

The refractive index or the index of refraction is the ratio of the speed of light in a vacuum to the speed of light in the material:

index-of-refraction-.png

Stars hugging the horizon will appear to twinkle more than other stars. This is because there are many more gradations of atmosphere between you and a star near the horizon than between you and a star higher in the sky.

stars.jpg
bhmpics.com

A star doesn't twinkle when seen from the near perfect vacuum on the Moon's surface or when viewed from a port on the International Space Station (ISS).

Planets shine with a steady light because they’re much closer to Earth and so appear not as pinpoints of light, but as tiny disks in our sky.

You can see planets as disks if you looked through a pair of good binoculars or a modest spotting telescope, a la Venus and its distinct phases (see blow), while stars still remain pinpoints. The light from these little planetary disks are also refracted by Earth’s atmosphere, as it travels toward our eyes. However – while the light from one edge of a planet’s disk might be forced to “zig” one way – light from the opposite edge of the disk might be “zagging” in an opposite way. The zigs and zags of light from a planetary disk cancel each other out, and that’s why planets appear to shine steadily.

venus 2.jpg
skymania.com

See: https://sciencequery.com/why-do-stars-twinkle/

* Scintillation: 1. the rapid fluctuations in the phase and amplitude of the wave. These are caused by local rapid variations in the refractive index of the medium through which the wave is traversing. 2. The act of scintillating. ... scintillation - the twinkling of the stars caused when changes in the density of the earth's atmosphere produce uneven refraction of starlight.

See: https://www.thefreedictionary.com/scintillations

Stars and planets and our friend, Old Mr Moon, are our nightly visitors. Some twinkle, while some burn with a steady reflected light, while the Moon is often bright enough to light our path.
Hartmann352
 
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Mar 4, 2020
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No one knows. We can only measure energy and the change in energy. AND we can only measure relatively SLOW changes in energy. Because of the response of our instruments.

If you ask for the rotation frequency of a proton or an electron, they will give you a figure, but that figure will be a math estimate, not a measured value.......we can't measure such things yet.

In the future, when we can chop time into much smaller units, we should be able to confirm or discredit present theories. For now, all we can do is compare math relationships.....and guess at the underlying meaning.

I believe we will find the truth of things a lot different from what we have been told.
 
Jul 29, 2021
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Reflected light has many studies and applications.

The most common:

  1. Reflected light changes polarization.
  2. Most of our experience of light reflection is seeing nearby objects. In this case reflected light is scattered due to rough surface (diffuse reflection).
  3. Scattering. Some light is scattered in all directions when it hits very small particles such as gas molecules or much larger particles such as dust or droplets of water.
The amount of scattering depends on how big the particle is compared to the wavelength of light that is hitting it. Smaller wavelengths are scattered more.

This is ‘Why the sky is blue’ part :)


In regards to another curious question ‘why stars twinkle’.

120 km of atmosphere with different temperature layers, turbulent flows, visibility does that.


And adding to the three most fascinating bliss to our eyes. During the dawn, near the horizon, the Sun, our star, is not a perfect disc. It’s edges also ‘twinkle’.
 

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