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Have you ever seen stars through a telescope or 

images of stars on the internet?   Have you ever 

wondered what stars are made of or if they are 

moving?

Telescopes are not the only way we can learn about celestial bodies.   

Scientists and astronomers use spectroscopy to learn more about 

objects in the sky.

Light from the Sun or another star, passes through a spectroscope or 

diffraction grating, which splits the light and produces a spectrum.

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There are three types of spectra that can be produced when light is 

passed through a spectroscope or diffraction grating.

A continuous spectrum is a complete, non-stop flow of colour.

An emission spectrum is a continuous spectrum with only precise bright 

bands, or emitted sections of light.

An absorption spectrum is a continuous spectrum, with dark lines, or       

areas of the spectrum that are absorbed.

All starlight will produce a spectrum, but each spectrum is unique, both 

in the type of spectrum produced, and the pattern of lines seen in the 

spectrum.

The three different spectra are produced, depending on the conditions 

in which the light is produced, or viewed.

What type of spectrum do you think our Sun emits?

When viewing a hot object directly, a continuous spectrum is 

produced.

When an object is heated to glowing, or viewed through a hot 

gas, an emission spectrum is produced.

When the source is viewed through a cool gas, an absorption 

spectrum is produced.

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Because we view our 

Sun through the 

atmosphere, which 

is much cooler than 

the Sun, we see its 

spectrum as an 

absorption 

spectrum.   In fact 

most stars will have 

an absorption 

spectrum when 

viewed on Earth.

But it is not only stars that produce spectral patterns.  

Any object heated to glowing and viewed through a 

spectroscope will produce a spectrum.

Chemists discovered that if they heated elements to glowing,   

or caused them to burn, each one would produce its own 

unique spectral pattern.

  These are simplified spectral patterns for a few elements.

   hydrogen

   helium

   calcium

   sodium

We can use the spectral patterns of stars to determine their 

composition.  By studying the unique lines of a star's absorption 

spectrum, and comparing it to known elements, we can tell what the 

star is made of.

Can you identify the two elements from the spectra on the previous 

page that are present in the spectrum of this mystery star?

If you identified hydrogen and sodium, you are correct.  

In these diagrams, hydrogen has three distinct lines: one in the red, one 

in the blue and one in the purple end of the spectrum.   Sodium has a 

very distinct pair of lines in the green-yellow area of the spectrum.

By lining up the spectra for hydrogen, sodium and the 

mystery star, we can see the patterns are the same.

   hydrogen

   sodium

  mystery star

We can also use spectral patterns to figure out if a star is 

moving towards us or away from us.

We can identify this movement by applying the principles of 

the Doppler Effect.  

The Doppler Effect is when a wave, like a wave of light, 

appears to be shorter or longer because it is moving towards 

or away from the viewer.

When a wave moves away                  

from the viewer, it appears                 

to stretch out or get longer. 

This is called a red shift.         

When a wave moves

towards the viewer, it 

appears to get pushed

together, or shorter. 

This is called a blue shift. 

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