light

Why do stars twinkle (and planets not)?

Hi,
I felt so embarassed that I finally had to find it out and now I am writing this short post about it. For few years, roughly, I am studying astronomy yet, I never knew why stars twinkle and planets not. I confess.

Stars twinkle because the light that reaches us goes through atmosphere and atmosphere is not very homogenous – smooth. Air refracts light and there is different temperature once in a while, humidity and so on, I think that lot of factors play the role. This causes the light of star to scatter a bit and creates the twinkling effect.

Planets do not do it. This is great because you can identify them extremely fast on the sky and you do not mistake them for some other bright star. Why? Their light still goes through atmosphere. Because they are not “point sources”. Stars are so far away that even with best telescopes we see them only as points. Planets with simple telescope on backyard already have shape. Some of their light scatters one direction, some the other and it basically cancels out creating nice image. This is also why it is better to go star-gazing in the winter, colder air does not create so much “noise” on the picture.

Dragallur

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Optics: 7) So is it wave?

Hi,
in last post I was talking about the experiment that proved that light is wave, it is creating interference in the double slit experiment instead of two lines which one would assume if it was behaving as a particle. (You can imagine bullets instead of particles).

double-slit-bullets

If light was behaving as particle

So I found out that the particle part of light is bit more complicated so I wont try to explain it so much in the PRO sense but rather in few words, if you are more interested check out this page: 1)

With this theory that light is just a wave there were finally find some problems.

If you would very accurately measure light on some spot and this light would be dimmer and dimmer, you should get dimmer and dimmer picture. But at one point there were just dots!

ccd-spot

As the light is getting dimmer, with very good camera you can see that some pixels get much more energy than other.

As you might understand this was quite confusing. Wave should not make pattern like this.

Soon it was found out that when you measure brightness you can find bumps that should not be there if light would be wave, rather it should be quite uniform.

Finally what was concluded from this is that light behaves both as wave and particle, the attribute is called particle-wave duality.

What was also found at this time (something like beginning of 20th century) is that light comes in quantas. This has very interesting effect. If you would walk away from candle and would be able to distinquish individual photons at one point the candle would not shine less and less because at one point there will be only one quantum coming to you and quantum is not divisible so it would start to disappear more and more often but it would always shine. More detail here:

It was also found that not only photon but also other subatomical particles behave like waves and particles. In 20th century it was tested with electrons and sure! They also made this interference pattern on detector.

Dragallur

PS: This is my 200th post!

 

 

 

 

 

Optics: 6) Experiment that changed our thinking

Hi,
today I will again write about optics but I have to return at the very beginning of 19th century when Thomas Young proved that light is behaving like a wave.

So there was this problem.

Newton thought that light has to be lot of particles, he called them corpuscles.

At the same time Huygens thought that light is behaving like a wave.

Then came this smart guy called Young. He conducted easy experiment to prove this.

The experiment is based on phenomena called interference of light. Imagine two people calling. When they both call at the same time. The called person is more likely to hear the call because they amplify the sound together. Now imagine that they want the person to hear some word that they are repeating again and again, such a word could be: RETURN!

When they call both at the same time it will make mega RETURN! And you can be sure that the person will hear it. But if one of them is slower by just a fraction of the time that it takes to say the word, whole message is destroyed:

1st person:   |return!|
–>  RETURN!
2nd person: |return!|
1st person:   |return!|
–> retuRneturn
2nd person:         |return!|
From the second example you can clearly see that if it is just a little windy the message may end up some thing like: “ertueruterut” and that is something you do not want. So light behaves in the same way. If both lasers are calling “red” at the same time you will get mega red (amplyfied red, with higher amplitude). If not well, you know what happens!

But analogies can take as only so far. There is one more problem. In my example if one person would call: “return” and the other “go away” the message should be destroyed. But with light, nothing happens, the words (colors) do not interact at all (in this way) because to interact the frequency has to be the same, this is called coherence of light.

So how did he use the interference of light to prove that light behaves like a wave? In his experiment imagine having a dark room with one small hole that leads to another two holes like this:

As the light passes through both slits it creates interesting pattern that is unique for waves.

If light would be particle you would see two lines on the right. But instead what happened was that at some places the amplitude was increased, as both sources (both slits) were calling (shining) at the same time or they were just moved by one word (one top of wave).[1] So some of the light is in consctructive interference (peaks on the black line) and some parts of the wave is in destructive (bottoms of the black line). This creates lighter parts and darker parts:

The double-slit experiment

And finally animation:

The light passing through both slits, green part is destructive, blue, red and yellow constructive.

Dragallur

If you are not still sure about this, watch the video below:

[1]By this I mean that one person starts calling: “return return return” and the second joins for the second return so they are moved by one period.

 

 

 

Cycling faster than light

Hi,
so while I was learning some optics, I bumped into this page that talked about refractive index which I was just studying. I wondered what is the highest refractive index ever found and there it was, not in number though I think we can calculate it.

Refractive index

Since you probably have not read my post about refractive index or you have not heard about it, it is dimensionless value that shows how much is light (electromagnetic radiation) slow in the medium where it travels and also how much it will change its direction when traveling through one medium into the other. You can calculate the index like this:

n=c/v

Where n is the refractive index, c is speed of light in vacuum and v is the velocity in the medium you are talking about. From this, it is easy to see that vacuum and only vacuum has the refractive index exactly 1 because there is nothing that blocks its way and you just divide speed of light in vacuum by speed of light in vacuum.

So as the index of refraction increases the only thing that can change is velocity in the medium and it is decreasing.

I found that scientists were able to create stuff in which the light was traveling in “only” 17 meters per second! This is 61.2 kilometers per hour. From steep hill or if you are really good cyclist you can be faster than that, though I think it is bit more easier and safer to do it in car.

So what is the refractive index of this miraclous stuff? Roughly 17,647,059. While normally n lies somewhere between 1 to 3.

What is this thing made of? 

… gas of sodium atoms – a high-tech version of the insides of the bulbs of street lamps – cooled to within a fraction of a degree above absolute zero … the effect of cooling reduces thermal effects, and this in itself contributes to the retardation of light.

There is also special state of matter created that packs those atoms closer together.

Dragallur

 

How to! 4) Go stargazing for the first time

Hi,
since I went out stargazing couple of times already, I would like to mention few things here for you, when you decide to go alone or maybe with your boyfriend/girlfriend stargazing. While I live on northern hemisphere all of these tips will be useful to south people.

Preparation

Check out the time when the sun sets where you live. This page is quite useful for that, you just need to insert your location.

It is quite useful to know what these terms mean, astronomical dusk is what you are looking for.

So you need to watch out for the time when first stars/planets appear which will be some time after the dusk, of course there must be clear sky which you need to check on Google forecast [1] or in TV.

Then while it depends on the time of year, it is good to take some extra clothes, because most probably you will be standing still for some time, so you might get cold.

How to stargaze

First option: take some sky map on paper with you. You can print some from internet but check if you are printing the right hemisphere. For this, you will need also some light, but not white, since you would never build night vision, take red, eyes are not so sensitive to it.

Second option: take your smartphone and download application with stars, I use Star Walk 2 Free and it is pretty good, especially because there is option for night vision so it is red, this is very useful though you must never lock your phone, because when you want to use it again the light from you display would pretty much destroy the night vision you build up.

What is night vision anyway? It is the activation of all your non color sensors in eyes and the adjusting of your vision in darkness by enlarging the part that collects light, it take about 30 minutes though you may see the effect even after 4 or 5.

Pick a good location

Be sure to pick a good location. If you are in big city, than make sure to drive to countryside because the light pollution would just waste your time.

Best is hill though it is good to be on some field or place where there are no trees.

Keep away from any buildings and streets. It is important for you to keep the night vision, one single mistake when you look in street light could destroy the whole process.

Enjoy 😉

Dragallur

PS: it is better to go stargazing when there is new moon, otherwise, full moon spoils the view of huge part of sky.

[1] To get in Google forecast just type “weather” and “your location”.

How does atom looks like?

Hi,
this was a question that friend of mine asked me on one contest I was this weekend. I was sure with the answer but after I said it I was not able to come up with the reason for it, at least I was not sure enough to say something clear.

So what exactly needs to happen for you to see it? There must be a photon which is reflected off the surface. How does this look like anyway on the atomic level? Well the light hits some electron in its way. There is lot of free space so this is why things that are not transparent can be if they are thin enough. The electron absorbs the photon, jumps to higher level (excitation), then it emits photon. Now on what you see depends upon its wavelength. So different materials will like to absorb different wavelengths making the object to have color. You can only change in what orbital you will have the electron so I guess that this is the fundamental difference between various colors of objects (though I did not check it).

So when electron emits the photon you simply do not know what the electron looked like. The only thing that you can get is just photon of some wavelength and there simply is not any way to look on some kind of surface of electron. Another factor is that the light has too big wavelength and you can not observe surface with that because the photon kind of just flows around and when you get to wavelength of the size of atom or smaller, the energy of the photon is so huge that the electron is anyway blown away.

There is nucleus too of course and normally photons do not get there because of this electron cloud around and nucleus is tiny. Otherwise from what I found it seems that again the proton and nucleus as whole is way too small and you can not actually map the surface.

 

But I was talking only about electrons and nucleus. You can actually see atom as whole. Not by microscope because visible light is way to huge. There is what is called Abbé difraction limit so you have to look for atoms in different way, using for example electrons (electron microscopes[1]) and then recreate the image using some cool physics, this is for example picture of silicon carbide:

And the one below is picture made by IBM of individual atoms that are shaped like the letters of IBM.

So while you can not see the atom, you can observe, not electron though or even the nucleus at least in ordinary way. You can for example measure energy or calculate the shape but you can not see them as physical objects.

Dragallur

[1]Electron microscopes observe how electrons bounce of the surface just like photons.

Read more: 1) 2) 3)

pearshaped-2WEB.jpg

The shape of Radium-224 nucleus

 

Optics 2) Snell`s law

Hi,
here it comes, here it goes! This is gonna be probably my first post where some real physics is involved (actually it is far too easy)! I am going to write about Snell`s law which is the law describing how light changes the angle of traveling when it enters to different medium.

First of all I have an experiment for you which goes as follows: you take a bowl which for the start will be empty except some small thing that will sink in water later on.
1) place your chin on the edge of table and move the bowl so you can see what is inside.

2) move it on the place where the edge will block your view and then place a water inside.

3) You should see the thing inside again!
This is because the light changes its angle of traveling which makes for example straw in bottle of water look so distorted (or hunter`s eye cheated when he is seeing the fish on different place then where it actually is (this makes water not look so deep as it actually is)), as that the higher part is not even connected sometimes to the lower one.
On the picture on the left you can see that the lower and upper part does not match which is because of the light which change the angle of traveling when entering glass then water then glass and air.

Fine, so what depends on how much will the angle change?
It is the difference between the speeds of light in both medium.

There is thing which is called refractive index: n. All mediums (which do let some light through) have some refractive index. Vacuum has 1, it does not change the angle of light. Air has about 1,0003 so you will usually see 1 also. But water has 1.33 and refractive index of glass ranges from 1.5 to 1.9 and the highest index known is for germanium=4.

When light enters another medium Snells law comes!

\frac{\sin\alpha_1}{\sin\alpha_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}
Btw. if you want to know n.. n=c/v (c is speed of light and v is the speed of light in current medium)

On the left you can see the example of light ray traveling from one thing to another. So for example if you did not know the angle in which it will fly in the second medium (water now) you would do this:
alfa=50°
beta=?
n(air)=1
n(water)=1.33

sin 50°/sin beta=1.33/1
sin 50°/1.33=sin beta
0.77/1.33=sin beta
0.58=sin beta
beta=sin^-1(0.58)
beta=35.5°
This is all beta about which I am talking here would represent theta two on the picture. So if you have enough information you can either get the angles or the speeds of light in mediums or the refractive indexes.

On the gif you can see pretty neat animation of how the waves of light are slower in the water and the red line clearly represents how the light is refracted.

Dragallur

Pictures except the first one are from wikipedia pages about refractive index and Snell`s law.
If you want to check out my first post about optics click here.
1st picture source

 

Optics: 1) Reflection

Hi,
here it comes, here it goes. I realized that if I want to really know something about astronomy I have to use physics. For now my first goal is to learn something about optics and particularly about binoculars and how they work and what is the math involved! Today I will write about very basics and it is reflection of light. Probably I will add something to it on my YouTube channel with some examples and I bet it will be fun!

When we are talking about optics and stuff around we assume that light or electromagnetic radiation behaves as particle (on the level where I am), the thing is that as rest of the really small particles like quarks and electrons and neutrinos, light behaves both as particle and wave which called wave-particle duality. This is very interesting but let it be for now.

As you see on the first picture from wikipedia article reflection, there is laser pointed on mirror which as you can see is reflected to the right.
This is important, the light gets reflected from mirror because photons bounce in the same angle from which the came.
On the right you can see the ray of light starting at P, reflecting from O and flying to Q. Both of the angles are are same from imaginative line that has 90° angle with the mirror. θr=θi  … r stands for reflected and i stands for incident. This also means that the angle of the ray and the mirror equals to the one on the other side. This is for mirror but of course other things are reflecting light too but because their surface is not smooth photons are flying all around and you want get the exact image of the thing that was emitting/reflecting the light first even if it is not absorbing any spectrum like snow. This is also the reason why it is dangerous to not wear anything across your eyes when you are a long time on place where is snow because over time all of this light can blind you.

This can happen in matter of couple of seconds if you look directly into Sun since the inside of the eye can be sun-burned in similar way like your skin and the damage may be permanent so watch out!

Dragallur

Why can not we travel faster than light?

Hi,
today I will write just a fun post about why we can not travel faster than light (even then it is desirable… as is written on mathbloggers cool blog: https://mathblogger101.wordpress.com/ ).

So there are some things that will start to happen when you go really fast.
First of all I would like to say that speed cannot be added because it would couse some trouble (like putting headlight of your car ON while driving).
There is simple equation which you can find on internet which says how speeds works when you are “adding” them.
Well another thing is that stuff is gaining mass while it goes faster but there is some effect only in higher speeds. (Athlete girls should not check their weight while running, they could be disappointed.)
It is exponential so you would need to give infinite amount of energy to system to get that speed, which would release infinite amount of heat and that would destroy everything, you just can not take that much of coal.
There is also another problem about which you maybe did not know.
Because this is electromagnetism whem moving around. If you read that post about EM you know that electromagnetic force carrier is photon.
What is the speed of photon? 300 000km/s
That means that photon which is responsible for your moving can not move you faster than it is traveling!
I will not be able to run faster with bricks for building if my maximal speed is 2m/s.

VSauce1 made a awesome point of what would happen with car traveling at speed of light and pushing its headlights on. If you know what is Doppler effect you can come up with the answer really quickly.. It is that WWWWŽŽŽŽŽMMMM of train or car traveling towards and than away from you but with sound. Same thing would happen to car at speed of light. For passenger inside nothing would happen, time would not happen because nothing like lenght which can travel light in one second would not happen for him because from his view light would not move any distance in one second…

Dragallur
PS: if you know about any reason why speed of light is 300 000km/s let me know because I dont