Download Astronomy Today, Chapter 3 Radiation 3

Astronomy Today, Chapter 3
Radiation
3-1 Information from the Skies
Intro
1. Why is the study of light so important in astronomy?
a. Can’t possibly (?) go to or near many objects
b. Cheaper to sit here, record, and analyze
c. Even if we went there, emitted radiation gives a lot of information
Light and Radiation
2. What is radiation?
a. = transmission of energy without a physical connection
3. Describe forms of radiation are not electromagnetic.
a. Cosmic rays are very fast H and He nuclei entering the atmosphere
b. α-particles and β-particles
i. Radioactive decay products
ii. α-particles are He nuclei; β-particles are electrons
4. Order the common divisions of the electromagnetic spectrum from largest to
smallest.
a. Radio
b. Microwaves
c. Infrared
d. Visible
e. UV
f. X-rays
g. Gamma rays
Wave Motion
5. Describe the characteristics of waves.
a. Energy is transferred without the movement of materials
b. Both energy and information are transferred
6. On a diagram of a wave, label the undisturbed state, wavelength, and
amplitude.
a. 0 on the Y-axis = undisturbed state
b. #1 = amplitude
c. #4 = wavelength
[http://en.wikipedia.org/wiki/File:Sine_voltage.svg]
7. In practical terms, when do we use wavelength, amplitude, and frequency?
a. Wavelengths
i. Colors/forms of light
ii. Shorter is more energetic
b. Amplitude
i. Strength of the signal
ii. The height of the wave
b. Frequency
i. How many waves pass per second
ii. Used to specify radio signals (AM and FM)
Diffraction and Interference
8. Distinguish diffraction and interference.
a. Waves spread out when they goes through a small hole = diffraction
b. Intersecting waves add together = interference
i. Can make the signal stronger = TV towers equally spaced
ii. Can cancel one another = noise-canceling headphones
c. Ripple Tank Simulator
3-2 Waves in What?
Interactions Between Charged Particles
9. What generates electromagnetic waves?
a. Moving and vibrating charged particles
b. Motion starts a disturbance in the particles electrical field
10. How does the strength of an electrical field and its disturbances vary with
distance?
a. By the inverse square law
b. Just like gravitational fields
Electromagnetic Waves
11. How fast do electromagnetic waves travel?
a. 3.00 x 105 km/sec in a vacuum
3-3 The Electromagnetic Spectrum
Atmospheric Blockage
12. Describe the transparence of Earth’s atmosphere.
a. Very transparent to radio and visible
b. only transparent to infrared very close to visible
3-4 The Distribution of Radiation
The Blackbody Spectrum
13. Describe the shape graph of the intensity emitted by an object versus its
wavelength.
a. Peaked but not symmetrical
b. Intensity falls off rapidly at shorter wavelengths
The Radiation Laws
Astronomical Applications
14. How can we calculate an object’s temperature given its peak wavelength and
vice versa?
a. Wavelength (in nm) equals 3,000,000 divided by T (in Kelvins)
b. The vice versa part
i. λmax = 3,000,000/K
ii. K = 3,000,000/λmax
3-5 The Doppler Effect
15. How is the wavelength of emitted waves affected by the velocity of the emitting
object?
a. Shortened if it’s coming towards you
b. Lengthened if it’s going away from you
16. How do we calculate the velocity of an object if we know the shift in wavelength
a. Apparent wavelength/true wavelength = 1 + (recession velocity/wave speed)
Astronomy Today, Chapter 4
Spectroscopy
4-1 Spectral Lines
Intro
1. How do astronomers generate spectra?
a. Prism or diffraction grating
Emission Lines
2. Contrast continuous, emission, and absorption spectra?
a. Continuous: all colors, no spaces
b. Emission: mostly black spaces, a few sharp lines of color
c. Absorption: mostly continuous with a few sharp black lines
3. How do the spectra of elements differ?
a. Different combinations of emission lines
Absorption Lines
4. How were absorption lines discovered?
a. The Sun’s spectrum has sharp, black lines across it
b. Some colors are missing
Kirchhoff’s Laws
5. How are continuous, emission, and absorption spectra generated?
a. Continuous from a hot object
b. Emission from a low density gas
c. Absorption from a continuous spectrum passing through a gas
Astronomical Applications
4-2 The Formation of Spectral Lines
Intro
Atomic Structure
6. How are the emission and absorption lines of atoms related?
a. Absorption
i. An electron absorbs a specific wavelength
ii. It is boosted to a higher energy
b. Emission
i. An electron emits a specific wavelength
ii. It drops to a lower energy
7. Compare the absorption and emission lines of an element.
a. They match
b. The element’s electrons absorb and give off matching wavelengths
The Particle Nature of Radiation
8. What is a photon?
a. An individual packet of electromagnetic energy having a specific
energy
The Spectrum of Hydrogen
Astronomy Today, Chapter 5
Telescopes
5-1 Optical Telescopes
Introduction
Refracting and Reflecting Telescopes
1. What is refraction? What is its physical basis?
a. = bending of light when it enters a medium of different density
b. Light goes slower in different substances
2. Sketch the formation of an image by a pinhole tube and a lens.
3. Describe chromatic aberration.
a. = colors separate when refracted
4. List several disadvantages of refracting telescopes.
a. Chromatic aberration
b. Difficult to support objective at end of the tube
c. Lenses deform when supported by their edges
d. Difficult to make perfect glass with two polished surfaces
5. What is the shape of the objective mirror in a reflecting telescope?
a. Parabola
6. How does the use of mirrors overcome the problems of refracting telescopes?
a. No chromatic aberration - light doesn't go through the glass
b. Largest mirror goes at the bottom - easier to support
c. Doesn't sag as much - supported on whole back
d. Only one polished surface
Telescope Design
7. Distinguish telescopes using the Newtonian and Cassegrain focuses.
a. Newtonian: eyepiece out at the top side of the tube
b. Cassegrain: hole in the middle of the big mirror, eyepiece goes in the
back; more compact, easier to point
8. How does a sidereal drive permit longer observations and photographic
exposures?
a. Sidereal drive compensates for the Earth's rotation
9. Distinguish alt-azimuth and equatorial mountings.
a. Alt-azimuth: angle above the horizon, angle around the horizon
b. Equitorial: must be aligned with the Earth's axis
Images and Detectors
5-2 Telescope Size
Intro
Light-Gathering Power
10. Describe the powers of the telescope and rank them from most important to
least important.
a. Light-gathering: bigger telescope see dimmer objects
b. Resolving power: accurate telescopes see in more detail
c. Magnifying power: larger images help only if the telescope resolves
well
Resolving Power
Building Very Large Telescopes
11. Describe the largest single-mirror telescope.
a. 8.4 m across, binocular in Arizona
5-3 High-Resolution Astronomy
New Telescope Design
12. What alternatives are being utilized to reduce the weight and cost of large
telescope mirrors?
a. Mirrors in sections
b. Deformable mirrors = adaptive optics