Spectrum and temperature of the stars

Uploaded by martintzvetomirov on 15.02.2009

Martin and Yoana present
Spectrum and temperature of the stars
Stars are enormous gas clouds with core made of heavier elements
People have always been asking themselves
How far away are they?
Can we measure them?
Can we see what they're made of and how hot they are?
We can't just go to them.
Voyager would need 76,000 years to reach the nearest star - Proxima Centauri
Then how can we explore them?
They seem so tiny.
Scientist have succeeded in using the only thing coming from the stars -
their light, to learn more about them.
Using spectral analysis, one can discover what a star is made of.
By finding the most intense light colour, scientist can measure its temperature.
But how is it all done?
If an element gets hot enough, it starts emitting light.
If we disperse that light using a prism, we could observe bright fringes at some places
Because those spots are uniquely spaced
every single one must be due to a specific energy level inside the atom
If we look at a slice of an atom we will notice unique energy levels
Electrons move to a higher level when they receive extra energy
When electrons fall to a lower level, they loose energy in form of light
which in turn creates a characteristic spectrum of an atom
Because each element has a different atom structure, each one has a unique spectrum.
Historically, Isaac Newton is the first to use the term "spectrum" in 1671
He noticed that when a light beam goes through a glass prism,
part of the beam is reflected by the glass, and what remains goes through
splitting into different colours.
He speculated that light consisted of differently coloured particles
and differently coloured light must have different speed.
Modern day spectrometers still use a prism
to produce the spectrum of a light beam.
Sir William Huggins was the first to attempt
to disperse light from celestial bodies
by using a spectroscope.
He built the first spectroscope, capable of decomposing light from distant stars.
Huggins expected a continuous spectrum just like the one produced by white light
instead he noticed dark lines.
He concluded that this absorption spectrum is produced by gases inside stars
which block certain colours
These dark fringes can be used to calculate what an object is made of.
That's how in 1868 Helium was discovered
by the French astronomer Pierre Janssen
He observed the emission spectrum of our sun
then he discovered a bright fringe with wavelength 587.49 nm
Later that year an English astronomer Norman Lockyer
concluded that this fringe is due to an element still unknown on Earth
later named Helium after the Greek word for sun - Helios.
But stars are telling us even more.
Spectrum analysis can be used to discover the largest intensity wavelength
Using Wien's laws we can deduce even the temperature of a cosmic body.
That's how they measured that the sun's temperature is 4,000 °C
because green light coming from it has the brightest intensity.
That's why plants are green down on Earth.
Using the Doppler shift, we can deduce the speed of celestial bodies.
Waves travel in air.
When a plane moves, waves in front of it compress creating high pitched sound.
Waves behind the plane stretch creating low pitched sound.
When the plane passes near you
you'll hear the famous Doppler shift
Same applies for light.
When an object approaches, light before it contracts
we call that a blue shift since objects look blueish
When an object is moving away, light stretches
making the object look reddish. This is called a red shift.
When a planet orbits a star
a characteristic wobble occurs about the common centre of masses
Observing the star using Doppler shift scientists can deduce
the speed of that motion
and thus discover new planets
Some of them may be teeming with alien life
So far about 400 planets have been discovered
None of them is expected to have life
due to bad conditions
such as being too close to the star or too far away from it.
Doppler shift has been used to discover how matter was created.
Astronomers observed that galaxies looked redder than they should
That only meant that they were getting away from us.
That's how they realized that long time ago
everything was confined in a tiny spot from which the Big Bang was produced.
Since then the universe is expanding
and scientists have different opinions about its future.
And we know all that thanks to light
the only thing we get from the stars.
Martin Marinov & Yoana Sandinska
Produced for Science and Mathematical school "Akademik Ivan Tsenov"
Vratsa, Bulgaria 2009