Telescopes
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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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Telescopes

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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

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


Refractor


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

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.


Chromatic aberration


Reflectors


Mt Palomar observing cage


Resolution

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


Alcor and Mizar


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

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.


“Seeing”

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

Good seeing is typically 1 arcsec.


Atmospheric distortion


Seeing


Atmospheric distortion


Discussion

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


Hubble Space Telescope


Mauna Kea


Keck primary mirror


Adaptive optics

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


Discussion

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


Discussion

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


Discussion

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


Atmospheric absorption


The Sun


Discussion

Why does the Sun emit light?


Discussion

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

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

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.


Discussion

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


Discussion

Where do you think that energy goes?


Discussion

Why isn’t the Sun a perfect blackbody?


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.


Discussion

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


Thermal equilibrium

The Sun is not measurably heating up or cooling down.


Discussion

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

As things contract gravitationally, they become hotter.


Discussion

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


Discussion

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

The Sun is not measurably expanding or contracting


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 – 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

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

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.


Discussion

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


Discussion

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


Discussion

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

1. Hydrostatic equilibrium

2. Thermal equilibrium


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.


Discussion

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


Discussion

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


Discussion

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


Discussion

What would happen if the Sun started to

contract? What would happen if the Sun

started to expand?


Discussion

What would happen if all fusion ended in the Sun?


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