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Telescopes. Discussion. If you had a Coke bottle and you wished to fill it with rainwater falling from the sky, how would you do it?. Telescopes Serve 3 Functions. To collect light To resolve fine detail To magnify the image. Discussion.

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If you had a Coke bottle and you wished to fill it with rainwater falling from the sky, how would you do it?

Telescopes serve 3 functions
Telescopes Serve 3 Functions

  • To collect light

  • To resolve fine detail

  • To magnify the image


Of the three telescope functions which do you think is the most important in astronomy and why?

Refraction(Marching Band Analogy)

What happens to the marching band if it hits a muddy part which causes the individual band members to slow?

Refraction(Marching Band Analogy)

Refraction(Marching Band Analogy)

Refraction(Marching Band Analogy)

Speed of light in glass
Speed of light in glass

Light moves slower in glass than in a vacuum

Speed of light through glass is different for different frequencies and each frequency has a slightly different focus.


The ability to separate two closely spaced objects, such as a double star.

The bigger your telescope objective the better your resolution will be.

Resolution and the atmosphere
Resolution and the atmosphere

Atmospheric turbulence limits the resolution of even the largest telescopes on Earth to about that of a 6 inch telescope.

Points of light
Points of light

Stars are so far away that they appear as points of light no matter how big a telescope you observe them with.

Bigger stars in photographs are simply brighter.


The apparent size of the stars as viewed through the telescope.

Good seeing is typically 1 arcsec.


What can astronomers do to try and improve resolution of their observations?

Adaptive optics
Adaptive optics

Actuators deform the primary mirror hundreds of times a second to try and remove atmospheric distortion.


Adaptive optic telescopes work best in the infrared region of the spectrum and not in the visible. Why do you think that is?


What do you think happens when very high energy gamma rays from space hit the Earth’s atmosphere?


Why can’t the very long wavelength radio waves make it to Earth’s surface?


Why does the Sun emit light?


How do you know the Sun is hot?

  • The setting Sun is red because

  • The Earth is rotating away from the Sun, so it is redshifted.

  • The setting Sun is cooler at sunset, so Wien’s law says the frequency of maximum emission shifts to lower frequencies thus appears redder.

  • At sunset the light has to travel through more of the Earth’s atmosphere, which has lots of absorption lines in the blue portion of the spectrum.

  • None of the above

Solar data
Solar Data

Radius: 109 Earth radii

Mass: 333,000 Earth masses

Mean density: 1.41 g/cm3

Composition: 74% hydrogen

25% helium

Luminosity: 3.86  1026 Watts

The sun as a big cosmic light bulb
The Sun as a big cosmic light bulb

Suppose every human being on Earth turned on

1000 100-watt light bulbs. With about 6 billion

people this would only be 6  1014 watts. We

would need 670 billion more Earth’s doing the

same thing to equal the energy output of the Sun.


Why is there less solar intensity at sea level than there is at the top of Earth’s atmosphere?


Where do you think that energy goes?


Why isn’t the Sun a perfect blackbody?

Line blanketing
Line blanketing

More heavy elements in a star’s atmosphere means more absorption lines, the redder a star will appear as higher frequency light is absorbed and re-emitted at lower frequencies.


The Sun releases lots of energy each second, what if it were cooling down over time. How could we tell?

Thermal equilibrium
Thermal equilibrium

The Sun is not measurably heating up or cooling down.


Given the composition of the Sun, why is it unlikely that it could be heated by the burning of wood or coal?

Kelvin helmoltz contraction
Kelvin-Helmoltz contraction

As things contract gravitationally, they become hotter.


Why do you think gravitational contraction leads to a temperature increase?


If the Sun is getting its energy from Kelvin-Helmoltz contraction, how could you prove this? Do you think this is an easy thing to do? Explain.

Hydrostatic equilibrium
Hydrostatic Equilibrium

The Sun is not measurably expanding or contracting

E m c 2
E = m c2

From Einstein’s Special theory of relativity, energy equals the mass times the speed of

light squared.

Matter is a form of frozen energy.

H and he
H and He

H – one proton

He – two protons and two neutrons

Neutrons are electrically neutral protons with slightly more mass

Fusion converts the sun s mass into energy
Fusion converts the Sun’s Mass into Energy

4 hydrogen atoms have a mass of 6.693  10-27 kg

1 helium atom has a mass of 6.645  10-27 kg

Thus, 0.048  10-27 kg are converted into energy.

Free neutrons are unstable
Free neutrons are unstable

A neutron, left by itself will decay into a proton, an electron and a neutrino.

Likewise a proton can change into a neutron by emitting a positron and a neutrino.

You can think of a neutron as a proton/electron pair.


Why must matter be so hot, 10 million K, for H to fuse into He?


How can atoms with more than one proton in the nucleus stay together? Why don’t they just fly apart?


Fusion keeps the Sun hot, but fusion requires the Sun to be hot. How did the Sun ever get hot enough to start fusion?

Modeling the sun
Modeling the Sun

1. Hydrostatic equilibrium

2. Thermal equilibrium

Pressure increases toward the center of the sun
Pressure increases toward the center of the Sun

To maintain equilibrium, the pressure below each

layer of the Sun must be greater than the pressure

above that layer.


What does this tell you about how the density changes with depth in the Sun?


What does this tell you about how the temperature changes with depth in the Sun?


According to the previous graphs, where is fusion taking place in the Sun? Explain.


What would happen if the Sun started to

contract? What would happen if the Sun

started to expand?


What would happen if all fusion ended in the Sun?