Category: light

Ask Ethan: Why Aren’t Rays Of Sunshine P…

Ask Ethan: Why Aren’t Rays Of Sunshine Parallel?

“I understand the sun is a really long distance from the earth, such that the paths photons take that strike the earth are pretty much in parallel. So why, when I see “rays of sunshine”, produced (I assume) by the sun shining through differing cloud densities, are they radial with their point of origin being at the apparent location of the sun in our sky?”

Seen poking through a cloud, trees or other opaque materials, sunbeams are one of the most surprising natural phenomena, when you think about it. There’s always scattered, ambient sunlight in all directions, and the bright sunshine is never visible as a ray when there aren’t clouds. Moreover, the light almost always appears to diverge away from the beam’s point of origin, rather than seeming to be the parallel rays you’d expect. So why is this the case? Why aren’t rays of sunshine parallel, like you’d expect? The fact of the matter is that the rays actually are parallel, even if they don’t appear so to your eyes. 

Seeing is believing, sure, but you won’t want to miss the actual physics of what’s happening!

Screens, Lasers and Symmetry

A couple of weeks ago, we discussed about the famous Photograph-51 and how
that led to the discovery of the Double Helix structure of DNA.

We
mentioned in that post that the best way to visualize that diffraction
pattern is by using a laser and pointing it on a helix from a ballpoint
pen.

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And in the previous post on pixels, we learned about how the RGB pixels arranged on a screen come together to render those beautiful images on your screen.

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                                        Source : Microworld

The pixel arrangement on a screen need not be periodic like shown above. In fact ,most manufacturers have their own unique type of representation ( see below )and the type varies with the type of application as well.

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As an amateur physicist you do not have a microscope but only a green laser as your tool, how would you go about finding which one of these arrangement your smartphone has ?

Visualizing pixel spacing using a LASER

For a fact, you know that:

if you shine a red light on a green or blue object, it will
appear black.

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                                              Source    

So if you take your green laser pointer and shine it on any of those pixel blocks, you know that you are only going to get green light from the green filter.

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The other two filters will absorb the green light.

And using that you can find out the type of pixel arrangement your smartphone has.

We will be testing it out with Samsung Galaxy S4 whose  pixel arrangement on the screen looks like so:

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Notice the oval nature of the green dots.

Let’s shine a green laser on the screen observe the resulting diffraction  pattern:

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The diffraction pattern that you obtain is the following:

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Observe that the dots on the image are not circles but ovals instead. This is due to the nature of the pixel arrangement on the Galaxy S4.

If you had a good red laser (which we did not) and tried this same experiment, you would get a pattern like so:

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You are also welcome to try it on a smartphone of your choice or any electronic display and compare it with the pixel arrangement of that particular device.

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This paper (from which the above image has been taken) runs through some more examples of the diffraction pattern that one obtains from common electronic components.

Have fun!

Related Interesting videos:

LCD Technology: How it Works

How a TV Works in Slow Motion – The Slow Mo Guys

* As with any diffraction pattern, you can measure the distance between the two dots and calculate the distance between two consequent pixels using the wavelength of the light source as given.

Shadows are not always black!Shadows are absolutely fascinating…

Shadows are not always black!

Shadows are absolutely
fascinating to play around with.

In this Exploratorium demonstration
you can see that a black shadow is only a subset of shadows that can be
formed on the screen.

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If you have multiple sources of light with different colors, then you can additively combine colors to get shadows of various shades.

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In this case where you have multiple sources of light, only when the object blocks off light from all three colored light sources do you get a black shadow.

Since we do not deal with multiple colored sources of light on a daily basis, go ahead, give this simple experiment a try. It’s totally worth it!

Have a good one!

** Other FYP explorations in Shadow : On disappearing shadows of Birds and airplanes

     

NASA Kepler’s Scientists Are Doing What …

NASA Kepler’s Scientists Are Doing What Seems Impossible: Turning Pixels Into Planets

“It isn’t the image itself that gives you this information, but rather how the light from image changes over time, both relative to all the other stars and relative to itself. The other stars out there in our galaxy have sunspots, planets, and rich solar systems all their own. As Kepler heads towards its final retirement and prepares to be replaced by TESS, take a moment to reflect on just how it’s revolutionized our view of the Universe. Never before has such a small amount of information taught us so much.”

When you think about exoplanets, or planets around stars other than the Sun, you probably visualize them like we do our own Solar System. Yet direct images of these worlds are exceedingly rare, with less than 1% of the detected exoplanets having any sort of visual confirmation. The way most planets have been found has been from the Kepler spacecraft, which gives you the very, very unimpressive image of the star you see featured at the top. Yet just by watching that star, the light coming from it, and the rest of the field-of-view over time, we can infer the existence of sunspots, flares, and periodic “dips” in brightness that correspond to the presence of a planet. In fact, we can figure out the radius, orbital period, and sometimes even the mass of the planet, too, all from this single point of light.

How do we do it? There’s an incredible science in turning pixels into planets, and that’s what made NASA’s Kepler mission so successful!

If the size of raindrops are uniformly small *(~0.5mm);  nature…

If the size of raindrops are uniformly small *(~0.5mm);  nature treats you with these exotic green, pink and purple fringes inside the bright primary rainbow, known as Supernumerary rainbows.

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We were able to observe these rainbows yesterday but it lasted only
for a couple of minutes. The above images have been corrected for
saturation in order to make the fringes predominant.

What makes these supernumerary rainbows really interesting is that you can’t use geometric optics to explain their formation and are forced to acknowledge the wave nature of light.

To know about the physics behind Supernumerary Rainbows, click here and explore. It’s truly amazing!

* When raindrops have different sizes, the differently spaced fringes overlap to a blur.

Why pilots use non polarized sunglasses ?

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Polarized lenses are not recommended for use in the aviation
environment.

While useful for blocking reflected light from horizontal
surfaces such as water or snow,

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polarization can reduce or eliminate the
visibility of instruments that incorporate anti-glare filters.

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Polarized lenses may also interfere with visibility through an aircraft
windscreen by enhancing striations in laminated materials (known as photoelasticity)

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     Photoelastic visualization of contact stresses on a marble in a C-clamp.

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and mask the
sparkle of light that reflects off shiny surfaces such as another
aircraft’s wing or windscreen, which can reduce the time a pilot has to
react in a “see-and-avoid” traffic situation.

– FAA

*Source:  Polarized v/s non polarized cockpit images

To light a candle is to cast a shadow, Shadows are fascinating…

To light a candle is to cast a shadow,

Shadows are fascinating to all living creatures; the subtle fear and curiousness of an entity that always follows you around everywhere you go  makes shadows extremely thrilling to explore.

How are shadows formed ?

Shadow is just a region where no light of rays are able to enter. 

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                             Relative sizes of the planets and the sun

When one pictures the sun one might be tempted to think (from its small apparent size in our skies) that it as a point source of light, but the size of the sun is HUGE!

If it were only a point source of light, one would never get the familiar umbras and penumbras that we see during an eclipse.

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In addition to the Umbras and Penumbras, there is another classification to these shadows – Antumbras

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If you were standing in the Antumbral region, you would experience an annular eclipse, in which a bright ring is visible around the eclipsing body

This is NOT the ‘shadow’ of the ISS

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                                Photo credit: NASA/Joel Kowsky

As you can see from the ray diagram, the ISS DOES cast a shadow and if you were on the ISS you would most certainly see it (orange box – umbra region)

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But
what you are witnessing from Earth in that amazing ISS photobomb of the 2017 Solar
eclipse is NOT a shadow but just the outline of the ISS against the
surface of the sun: An annular eclipse of the ISS.

On disappearing shadows of Birds and airplanes

The shadows of airplanes and birds when they are closer to the land are definitely a common sight.

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                                                    Source

But it seems as if that when these birds and airplanes are flying way up in the sky, they are not casting any shadows to the ground !

Although it is incorrect to say that they don’t cast shadows at all, it is true that their ‘shadows’ never reach the ground. Here’s an illustration:

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                                                    Source

How does one place a screen near an object flying 30000ft above the ground to witness the shadows?

Well, the clouds in the sky can most certainly act as screens to capture the shadows of the airplane when its flying high up in the sky. ( This is an optical phenomenon known as ‘Glory’. )

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Shadows are just breathtaking, aren’t they?

fuckyeahphysica: Try bringing two of your fingers closer in the…

fuckyeahphysica:

Try bringing two of your fingers closer in the back drop of a light source and you would observe this:

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Long before your fingers actually touch, the edges magically seem to touch each other. How is this even possible?

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Transit of Venus

When scientists were observing the transit of Venus from Earth i.e when the planet Venus passes directly between the Sun and Earth,they faced a similar problem. 

At the moment when Venus should
nearly touch the edge of the sun, the circular planet began to elongate.

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                                                PC: NASA

And they noticed the same phenomenon for Mercury as well (which has no atmosphere).


What is causing this optical phenomenon?

The physics behind this beautifully bizarre optical phenomenon will be revealed tomorrow on FYP!.

But since this is something that you can all try at home, we strongly encourage you to play around with this and get a feel for it. It requires only your hands and a source of light.

Once you do, try to hypothesize  a solution for this behavior.

Have fun!

The black drop effect

Let’s take a closer look at this optical phenomenon by projecting your hand on to a screen and bringing the fingers closer together.

Observe the behavior of the penumbral region of the shadow i.e the less darker region:

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Ahhaa… Notice that even though my fingers are not touching each other in the last image, if you see the shadow it seems as though they are!

This is because of when two penumbral regions of the shadow overlap, you get a much darker region in the middle. Here’s an illustration:

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Yes in reality, you do observe gradients of darkness in between the two objects like so:

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BUT our eyes are not that great at handling such fine contrasts in darkness; It clips off the less darker regions between the two shadows and replaces it with the surrounding darker region.

A similar response is rendered by the camera’s noise suppression algorithm too. That’s why you get that bulge connecting the two umbras irrespective whether you view it through your eye or through the camera.

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In the case of the camera, this can be rectified using the appropriate tools and processing, whereas in the case of the eye you are stuck with it.

The case for Venus Transit

You can observe the same clipping phenomenon (called Black drop effect) that we talked about if we project the image onto a camera instead of a screen:

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If the light source were the sun, the object were Venus instead of your fingers, and the screen were your eyes, you get this fuzzy shadow behavior commonly observed during the transit of Venus.

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This is not a droplet, but the black drop effect observed during the  transit of Venus

The case for Diffraction (OPEN DISCUSSION):

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When I posed this question to a lot of my friends, their first response was Diffraction but honestly I couldn’t visualize this phenomenon with Diffraction.

I spent a lot of time playing with a laser module trying to figure out how Diffraction would fit into this explained but I am unable to come up with a reasonable argument for it.

If you have a valid explanation of this using Diffraction(or other), please enlighten me and the rest of the community. I personally would really love to know.

Thanks and have fun!

** If this fascinated you, check out this stackexchange post for more

Try bringing two of your fingers closer in the back drop of a…

Try bringing two of your fingers closer in the back drop of a light source and you would observe this:

image

Long before your fingers actually touch, the edges magically seem to touch each other. How is this even possible?

image
image

Transit of Venus

When scientists were observing the transit of Venus from Earth i.e when the planet Venus passes directly between the Sun and Earth,they faced a similar problem. 

At the moment when Venus should
nearly touch the edge of the sun, the circular planet began to elongate.

image
image

                                                PC: NASA

And they noticed the same phenomenon for Mercury as well (which has no atmosphere).


What is causing this optical phenomenon?

The physics behind this beautifully bizarre optical phenomenon will be revealed tomorrow on FYP!.

But since this is something that you can all try at home, we strongly encourage you to play around with this and get a feel for it. It requires only your hands and a source of light.

Once you do, try to hypothesize  a solution for this behavior.

Have fun!

Shadows of Mount Everest  & K2 at SunriseMount Everest might…

Shadows of Mount Everest  & K2 at Sunrise

Mount Everest might be tiny when compared to the size of the earth and as a result we might not be able see it’s shadows on the moon.

But it would be crazy not to acknowledge the breathtaking shadows that it casts during sunrise.

* Previous post: Why don’t we see the shadow of the Everest on the moon?