# Spectral line

Hi,
here comes another solo post this time about spectral lines. Do you know how is it that we know the compounds of stars far away? Or what is the surface of Pluto even that we did not land on it? All of this and many other things have to do with spectral lines.

So spectral line is bright or dark electromagnetic radiation in the rest of the radiation. This means that when you have some light from some star coming to you, you will also have some planet few kilometers away which will be reflecting light and this light will be dimmer, that is spectral line and what you can get from this spectral line is what were those atoms that reflected the light towards you! This is incredibly powerful!
Ok so the first spectrum is the continuous spectrum which is the one I mentioned first. The second one is emitted spectrum. It it the one that planet reflected (emitted) towards you from the planet or something. The last is the absorbed radiation, the one which the planet absorbed by its surface.

So what scientists do with this is that they measure what wavelengths of radiation were emitted towards them and then they compare it with the stuff that is around us and what it emits. “Easily” they know what kind of element it was.

This is called spectroscopy!

Part of this is the red shift.
Red shift is the effect of Doppler effect which does not applies only to sound (train going towards and away from you). Even light when the object is moving fast enough can be observed to either go to red part (away from you) of spectrum or blue (towards you). Usually except the local cluster of galaxies, stuff in Universe is in red shift because it is going away from us.
Actually what I just realized is that when you are running everything in front of you is bluer (if you run towards it).

Ok finally here comes the math of red shift!

The amount of red shift is Z. You can get this value by few different ways and I dont understand some but you can look them up.

So if you want to count the speed in which the thing is going away from you there are two ways:
The less accurate applies only if Z is smaller than 1.
v=c*z — if z is bigger than or equal to 1 you would get that the thing is going in speed higher or equal to speed of light. For this the more accurate way comes:
(To know velocity just multiply both sides by speed of light)
You can see that the right side does very nice thing. Every time, no matter how big or small z is you will always get the difference numerator and denominator 2. BUT when you divide it, it is whole different story since 2/4 is much further from 1 then 998/1000. So as you increase z then the speed is coming closer and closer to speed of light.
I will add how it is with distance but I have some problems there with it which I have to figure out…
EDIT: ok I know it now so:
when you want to know distance from you of the object:
d=c*z/H
H is the Hubble constant which I will mention probably some time.

The largest observed red shift is the red shift of one quasar which has red shift 4.25 and is moving at the speed of 0.93 c … here is the calculator for red shift.

Dragallur