Chapter 5 - Chapter 6 Flashcards
What causes the changes in tides?
The differential gravitational force from the Moon stretched the Earth, raising symmetric tidal bulges.
What do tides affect?
Tides affect both water and land, but since water flows more readily we mostly observe changes in water level
two tidal bulges model?
- take the total gravitational force from the moon
- Differential gravitational force from the moon (subtract the average force)
This causes the water to rush to locations along the Earth-moon axis. to add to this the earth is also rotating
How does Earth’s rotation affect the two tidal bulges model?
Earth’s rotation causes friction. Friction pulls the tidal bulges slightly below the Earth and Moon axis.
What about the Moon’s tides?
Moon is smaller, so the difference in force between the Earth-side and far side is smaller. Also no easily moved water on the moon.
What forces affect tides and the moon?
The moon’s gravity on earth’s tidal bulges acts as a torque to change the Earth’s angular momentum. In the past the Moon rotated faster, causing a similar misalignment of its tidal bulges.
How did earths forces affect the moons rotation?
Torque from the Earth’s gravity slowed the Moon’s rotation and locked into synchronous rotation. Once the Moon’s rotation slowed enough that it was equivalent to its orbital period, the bulges are now perfectly aligned, so no further slowing occurs
What are two properties of Light?
- Light behaves like a wave, creating an interference pattern.
- Under other circumstances it behaves like individual particles (photons)
Wavelength vs frequency?
wavelength is the distance between peaks. Frequency is the number of times each second that the electric (and magnetic) field vibrates up and down at any point.
Wavelength formula
lamda * f = c
lamda is wavelength
f is frequency
c is the speed of light
Light as a Photon
light also behaves as a particle called a photon. Each photon carries a tiny fixed amount of energy proportional to its frequency.
Energy formula
E = hf
E = h(c/f)
h is Planck’s constant
E is the photon energy in joules or EV
The Electromagnetic Spectrum
gamma rays, x-rays, ultraviolet, visible, infrared, microwave, and radio. (shorter wavelength = highest energy and highest frequency)
How does matter interact with light?
matter emits light.
matter absorbs and reflects light.
matter transmits light.
What is a spectrum
A spectrum is a plot showing how much light is emitted at each wavelength
2 laws of thermal emission
- A hotter object emits more light per unit surface area than a cooler object at all wavelengths
- the peak wavelength is shorter (bluer)for hotter objects and longer (redder) for cooling objects.
What is Wein’s Law?
hotter temperature objects have their peak emission at smaller wavelengths. (therefore are blue)
Why is the sun white?
the sun’s peak wavelength is green but it emits all of the colours of visible light looking white.
Why is the sky blue?
Air molecules in Earth’s atmosphere scatter shorter wavelengths, Blue and purple light bounces around the atmosphere before reaching us
transitions from one energy level to another
energy level refers to the amount of KE and PE of an electron. Transitions require the exact amount of energy. photons passing through (wavelength) can excite a transition.
What do absorption line spectra show?
absorption lines spectra show where the light of a specific wavelength has been absorbed
What do emission line spectra show?
Emission line spectra show us where lines at specific wavelengths are emitted
How are emissions and absorption spectra linked?
Emission and absorptions lines occur at the same wavelength for the same element/molecule
But light waves also undergo the doppler effect
Redshift: object is moving, Rest Frame: object is at rest relative to us. Blueshift: object is moving towards us.
When does the doppler effect happen
Only when it is in line with where you are standing
Classical Doppler Shift Formula
((delta)lamda)/ lamda = v/c
(Delta)lamda) = shift in wavelength
lamda = rest wavelength
v = velocity of the emitter
c = speed of light
Why is the Doppler shift important
We measure the Doppler shift in stellar spectral absorption lines to determine the star’s velocity of about the center of mass.
Two main properties of a telescope
- Collecting Area: how many photons can it collect per second?
- Resolution: how crisp of an image can it produce?
Both depend on the size of the telescope, for telescopes, “size” = “diameter of primary optic”
What is the angular separation
we can distinguish that there are two stars, not just one
The diffraction limit
because of the diffraction of light, the best possible angular resolution for a telescope is related to the wavelength of light and the size of diameter of the telescope
Angular Resolution of smaller/larger telescopes
Larger telescopes have better angular resolutions
What is the link between wavelength and telescopes?
Different wavelengths show us different features
What about magnification?
We can use additional lenses to control the magnification and field of view of the image. But, just like zooming, you can’t get past the resolution limit.
Refracting Telescope?
Refracting telescope: Use lenses to focus light.
- Lenses were easier to make therefore the refracting telescopes were first.
- Refractors are very long since light follows a fairly straight path through them.
- Lenses very large are very impractical (super heavy)
Reflection Telescope?
Reflective telescope: Use mirrors to focus light.
- Mirrors are made of glass with a thin coating.
- Since the light path can reflect back and forth, these don’t need to be as long.
- Large modern telescopes are reflectors.
- Also sag under their own weight, or due to temperature/wind
- Largest telescopes are segmented
- Solution is to build smaller segments and use computers, sensors, and motors to control their shape.
