Spectroscopy.

 When you look up at the stars, what can you know? You might have heard that blue stars are hotter, the red ones are cooler and will be able to catalogue them as hot and cold. But what if I told you that just by analysing starlight, astronomers are able to know so much more such as their densities, their motion and things like that?This is where spectroscopy comes in.Spectroscopy deals with splitting up light and analyzing it. It is, undoubtebly, one of the most useful tools in the hands of scientists.

There are three types of spectra that can be produced by a body

1. Continuous spectra

2. Emission spectra

3. Absorption spectra


Kirchhoff’s laws
There are three laws known as Kirchoff’s laws of spectroscopy. These state the conditions that are required to obtain the spectra of different types.They are
1. In order to get a continuous spectrum,there has to be a hot material under high pressure. If you were to take the spectra of an object like a lightbulb, you will get a continuous spectra.
2. To get an emission line spectrum, there is need of an excited gas under low pressure that has a low density.(an excited state is when electrons jump from a lower energy level, or its ground state, to a higher energy level)
3. You get an absorption line spectrum when ER from a hot energy source passes through a gas with low density. In other words, light from a source of a continuous spectrum passes through this gas. Stars happen to have absorption spectrums.
 
 Kirchoff’s laws state the conditions for each kind of spectra to be formed. So, the next time you look at any spectra, you know how it is formed.
Now coming to the most interesting part What can spectroscopy tell us about?
Composition
Each element absorbs or emit only certain wavelengths of light. So, if you know the mark of these elements, you can figure out the chemical composition of the object observed. Given below is the absorption spectra of Hydrogen.

temperature
We can figure out the temperature of a star by using something called a blackbody curve. Wien’s law- This law states that the maximum wavelength is inversely proportional to the
Temperature of the body. The formula is,
λpeak = b T
Where b is the Wien’s constant ,T is the temperature and λ is the wavelength.
When you plot something called a blackbody curve, just figure out the maximum wavelength emitted. By that you know what the surface temparature of the object you observe.
Density
A star with more density in its outer layers will have smudged spectral lines.Stars that have a relatively uniform density are going to have thinner,clearer lines.
Motion
To calculate if an object’s motion relative to the Earth.
You might be familiar with the Doppler effect. This effect also applies to the forms of electromagnetic radiation. If a particular object is moving away from us, its wavelength
 
 decreases. This would cause the object’s spectral lines to shift towards the blue end of the spectrum. An object that shows this effect is said to be blue shifted.The opposite is true too. An object moving away from us would have its spectral lines shifted towards the opposite end, the red side of the spectrum. If you want to calculate how fast it is moving, measure that teeny change in its spectral lines
What if you saw the spectrum of an object that has thick lines?
Imagine a ferris wheel. Two of your friends are riding on its opposite ends. When the wheel starts rotating, at times, friend A would be at the top and friend B would be at the opposite end . You will notice that friend A is moving away from you, while friend B is coming closer to you. Something similar happens to rotating objects in space.One part is shifting toward the blue end while the other is moving towards the red end of the spectrum. This causes spectral lines to be thicker as the object is both moving towards and away from us.
In other words, the object is rotating.

That is why spectroscopy is so amazing! 

Thanks for reading!

Credits; Image 1 taken from- https://www.pinterest.co.uk/pin/545217098627952623/

Image 2 taken from- https://physics.stackexchange.com/questions/238236/why-absorption-spectum-is-not-identical-t o-emission-spectrum


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