Spectrum of Stars: Explaining the Spectral Lines of Stars

[ehabmozart]

I've been deep into this topic for a couple of days and it is becoming just more and more confusing. I am yet a beginner so i would like explanations to be detailed and easy. Moving directly, my doubt is.. We treat stars as black bodies which emit radiation... From where did the stars originally get their energy or atleast energy of all wavelength from.. Fusion?? .. Secondly, how do we detect the elctromagentic radiation.. Is it by naked eyes on a specific telescope or something.. Importantly, it is given in my book the spectral lines of different stars... O B A .etc... How u would clasify that for example all O class stars would have the same composition.. And i can see a trend in the lines from O to M class... I just need a detailed explanation of these spectral line.. And how would an object which orignally showed contionous spectrum would actually show and absorption spectrum?? I really really need the help.. It is urgent... Pass by any sentence.. It is worth reading every word in this topic... Please reply... Thanks in advance to whoever dominates in giving me the answer

 

[Drakkith]

I've been deep into this topic for a couple of days and it is becoming just more and more confusing. I am yet a beginner so i would like explanations to be detailed and easy. Moving directly, my doubt is.. We treat stars as black bodies which emit radiation... From where did the stars originally get their energy or atleast energy of all wavelength from.. Fusion?? ..

Initially each star was a huge cloud of gas and dust spread out in an area of space. At some point this gas was made to be unstable, perhaps by a supernova shock-wave in the interstellar medium, and began to collapse under the influence of gravity. As gas collapses or is compressed it heats up. An object that is above absolute zero emits a spectrum of radiation that depends mostly on it's temperature and a little bit on its composition. As the gas collapsed further the temperature rose higher and higher. Finally, once the gas had collapsed into a large spherical shape, the temperature finally reached the point where hydrogen could begin fusing in it's core, and thus the star is born.

One key thing here to understand is that the star gets its energy initially from gravitational collapse. Just like a falling object has energy, a collapsing gas cloud does too. Fusion effectively replaces the gravitational energy lost by radiation.

Secondly, how do we detect the elctromagentic radiation.. Is it by naked eyes on a specific telescope or something..

We use spectrographs on a telescope to separate the light into a spectrum, like a prism does to white light, and a camera to record the light itself.

Importantly, it is given in my book the spectral lines of different stars... O B A .etc... How u would clasify that for example all O class stars would have the same composition.. And i can see a trend in the lines from O to M class... I just need a detailed explanation of these spectral line..

See here: http://en.wikipedia.org/wiki/Stellar_classification

And how would an object which orignally showed contionous spectrum would actually show and absorption spectrum?? I really really need the help.. It is urgent... Pass by any sentence.. It is worth reading every word in this topic... Please reply... Thanks in advance to whoever dominates in giving me the answer

Stars do not show a continuous spectrum, although they may appear to if your instrument isn't sensitive enough to separate or record the lines.

 

[Chronos]

Actually, stars do emit a continuous spectrum, but, include both emission and absorption lines.