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As was seen in previous units, distances within space are so huge that actually going to a star and observing it in location is impossible. Our knowledge of the Universe is entirely based on observations of emitted Electromagnetic radiation.
As was seen in previous units, distances within space are so huge that actually going to a star and observing it in location is impossible. Our knowledge of the Universe is entirely based on observations of emitted Electromagnetic radiation.
Note - As of May 2016, a second method to observe the Universe was discovered. Scientists have now proven that it is possible to observe the collision of two Black Holes by detecting the Gravitational waves the collision emits.
Note - As of May 2016, a second method to observe the Universe was discovered. Scientists have now proven that it is possible to observe the collision of two Black Holes by detecting the Gravitational waves the collision emits.
The Electromagnetic radiation that can be observed can, however, give a great deal of information about a star.
The Electromagnetic radiation that can be observed can, however, give a great deal of information about a star.
By simply observing the colour of a star, information about the Temperature (and therefore the composition/size) of a star can be found.
By simply observing the colour of a star, information about the Temperature (and therefore the composition/size) of a star can be found.
The diagram below shows the colour of some notable stars visible in the northern night sky :-
The diagram below shows the colour of some notable stars visible in the northern night sky :-
The colour of a star is directly related to its surface temperature, with red stars being relatively cool ( ~3,000 K ) and blue stars being relatively hot ( ~ 18,000 K ).
The colour of a star is directly related to its surface temperature, with red stars being relatively cool ( ~3,000 K ) and blue stars being relatively hot ( ~ 18,000 K ).
The image below is a time-lapse image of the constellation of Orion, in which the camera has been continually brought out of focus to emphasise the stars' colours :-
The image below is a time-lapse image of the constellation of Orion, in which the camera has been continually brought out of focus to emphasise the stars' colours :-
Black-Body Radiation
Black-Body Radiation
Any object with a Temperature above absolute zero will emit E-M Radiation. The Wavelength of this emitted radiation depends upon the Temperature. The higher the Temperature, the shorter the Wavelength of the peak emitted Wavelength.
Any object with a Temperature above absolute zero will emit E-M Radiation. The Wavelength of this emitted radiation depends upon the Temperature. The higher the Temperature, the shorter the Wavelength of the peak emitted Wavelength.
In order to describe qualitatively how the Temperature affects peak Wavelength, the concept of a class of object called a Black-Body object.
In order to describe qualitatively how the Temperature affects peak Wavelength, the concept of a class of object called a Black-Body object.
A Black-Body object is a hypothetical object that is a perfect absorber and radiator. This means that absolutely no E-M radiation is reflected from it.
A Black-Body object is a hypothetical object that is a perfect absorber and radiator. This means that absolutely no E-M radiation is reflected from it.
A Black-Body will emit radiation over a range of Frequencies, with a peak Wavelength which is dependant on to the Temperature of the object. The diagram shows a composite image of four Black Body radiation curves, each at a different Temperature:-
A Black-Body will emit radiation over a range of Frequencies, with a peak Wavelength which is dependant on to the Temperature of the object. The diagram shows a composite image of four Black Body radiation curves, each at a different Temperature:-
As can be seen in the above diagram, as the Temperature of the object increases, the peak Wavelength moves towards the shorter Wavelengths.
As can be seen in the above diagram, as the Temperature of the object increases, the peak Wavelength moves towards the shorter Wavelengths.
The video below shows a Steel nut being heated by an induction coil:-
The video below shows a Steel nut being heated by an induction coil:-
Note - As the Temperature of the nut increases, the colour of the peak emitted Wavelength shortens, giving the changing colour.
Note - As the Temperature of the nut increases, the colour of the peak emitted Wavelength shortens, giving the changing colour.
The diagram below shows how observing the colour of a star, the peak Wavelength can be identified and (if we assume the star acts as a Black-Body), its Temperature can be found:-
The diagram below shows how observing the colour of a star, the peak Wavelength can be identified and (if we assume the star acts as a Black-Body), its Temperature can be found:-
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