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Unit 1, Chap. 4 Astronomy Test for Jaunty30
Terms in this set (19)
Images can be formed through reflection or refraction
Differential refraction leads to chromatic aberration:
Image acquisition is by charge-coupled devices (CCDs) - an be read out and reset quickly. Images can
be further refined by computer smoothing.
Two reasons why larger telescopes are more desirable:
• Larger telescope has better resolution
• Larger telescope can gather more light.
Light-gathering power In-proves detail
Brightness is proportional to square of radius of the mirror
• Similar to optical reflecting telescopes
• Prime focus
• Less sensitive to imperfections (due to longer wavelength); can be made very large
• Largest Radio Telescope: 300-m dish at Arecibo, Puerto Rico.
• Longer Radio Wavelength means poorer angular resolution. However there are some real advantages
• Can observe 24 hours a day. Clouds, rain, and snow don't interfere
• Observations at different radio wave lengths get totally different information
• Interferometry can combine information from several widely-spread radio telescopes as if they came from a single dish. The resolution will be that of a dish whose diameter equals the largest separation between dishes.
• Interferometry can give radio images whose resolution is close to optical:
• Interferometry can also be done with visible and infrared light, but it is much harder due to shorter wavelengths:
There are many observatories now operating in space.
• Infrared radiation can often image where visible radiation is blocked; generally can use optical telescope mirrors and lenses
• Ultraviolet observing must be done in space, as the atmosphere absorbs almost all ultraviolet rays
• X rays will not reflect off normal mirrors but they will reflect at a very shallow angles; they can be focused with concentric cones.
Much can be learned from observing the same astronomical object at many wave-lengths. Here, the Milky Way.
Measuring the Velocity of Light
Distance is the measure path from the light source, to the rotating mirror, to the stationary mirror, back to the rotating mirror and to the observer.
Time is the time it takes for the spinning mirror turn between reflecting angles.
The velocity of light =
C = D/T = 500,000 km/sec
The wave nature of light
Refraction is a property of a wave that causes it to change direction as it passes through a different medium. The longer wavelengths are bent the least, the short are bent the most.
Diffraction allows the waves to interact with each other, sometimes cancelling and sometime reinforcing.
Visible light is part of an electromagnetic spectrum whose waves travel at the velocity of light. All parts of the spectrum have in common that their waves have both a magnetic and an electric component.
There is no limit to the lengths of the electro-magnetic waves from the very short gamma waves to the very long radio waves. The various sections of the spectrum have different names but they have many features in common.
When solids, liquids or gas at high pressure are heated to incandescence and viewed with at spectrograph the results are Continuous Curves of a characteristic shape. These results are also known as Black Body Curves or Thermal Curves.
Particle nature of light
Einstein described the second nature of light as a bundle of energy which was inversely proportional to the wavelength,
Spectral lines are images of the entrance slit on the photo plate in each of the colors contained in the original light.
The Niels Bohr model of the atom was a major leap forward in our understanding of atomic structure, but it was not the final answer. Bohr postulated that electron orbits about the nucleus are quantized.
Law 1: A hot opaque body, such as a perfect blackbody, or a hot, dense gas produces a continuous spectrum-a complete rainbow of colors without any spectral lines.
Law 2: A hot, transparent gas produces an emission line spectrum-a series of bright spectral lines against a dark background.
Law 3: A cool, transparent gas in front of a source of a continuous spectrum produces an absorption line spectrum-a series of dark spectral lines among the colors of continuous spectrum. Furthermore, the dark lines in the absorption spectrum of a particular gas occur at exactly the same wavelengths as the bright lines in the emission spectrum of that same gas.
LIGHT AND MATTER:
Photons: Produced and absorbed by electron transitions
Transitions: Movement of electrons between energy levels
Energy levels: Stable values of energies for electrons
Excitation: When an electron is in any level except the ground state by collisions between atoms or by absorption of photons.
Original Doppler Experiment
Doppler used friends with 'perfect pitch' to make the measurements.
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