Astronomy 100-09 Exam 2 Fall 2022 Flashcards
the sun: what is the photosphere?
the photosphere is the sun’s visible disk that is produced by a thin layer of the sun
the sun: what are granulation and sun spots? ( surface phenomena)
- granulation: tops of convective cells
- sun spots: regions of intense magnetic energy and allow for convection allowing gas to cool down
the sun: what temperature is the suns surface?
11,000 degrees f or 5800 k
the sun: does the sun have a solid definite surface?
no
the sun: any possible fuel for the Sun must account for what 2 things?
-energy output per time (i.e. luminosity)
-duration of output
the sun: what is the formula for duration ( solar energy generation)
duration= amount of fuel / rate of consumption
the sun: what was the first clue to actual energy source came in 1905?
E=mc^2
the sun: what 3 things to you need enough of to sustain thermonuclear fusion?
temperature, pressure and density
the sun: what is hydrostatic equilibrium?
outward pressure is balanced by inward gravitational force
the sun: what is the random walk?
high density of plasma in the core and radiative envelope causes
repeated scattering of light as it passes amongst the atoms
light: what can we say about light as a physical phenomenon?
- fastest phenomena in the universe
186,000 mi/s or 299,792 km/s
-speed of light in a vacuum is a universal constant - white light is composed of a spectrum
roygbv ( red orange yellow green blue violet )
light: what is Newton’s definition of light?
-“corpuscular” theory; light is composed of undetectable particles
-explains propagation through a vacuum
light: what is Huygens’s definition of light?
-wave theory; light is a form of wave
* diffraction
* interference
light: what is Maxwell’s definition of light?
electromagnetic wave theory; light propagates as an oscillating electromagnetic field
light: what is a wavelength?
distance between two identical points on the waveform
light: what is the standard wavelength unit and what power does it equal to?
- the standard unit for wavelength is angstrom
- 10^-10 m
light: what do blue and red colors represent in wavelengths?
- red: longer wavelengths
-blue: shorter wavelengths
light: what is frequency and what is the formula?
-frequency (v): number of waves per second that pass a
stationary point
- v= c / wavelength
light: is wavelength and frequency inversely related?
yes
- high frequency means lower wavelength
- low frequency means long wavelength
light: how is frequency measured?
-measured in cycles per second: 1 Hertz (Hz) = 1/s
visible light estimates to 600 million MHz
light: how did Einstein define photons?
-light is composed of “packets of energy” (i.e. particles)
-every photon has a discrete amount of energy and momentum
light: what is the formula for photons?
E= hc / wavelength = hv
light: what does h represent and what does it equal to?
- Planck’s constant
- 6.626 x 10^-27 erg x s
light: what does 1 watt equal to?
10^7 ergs/s
light: what do visible photons equal to?
10^-12 erg
telescopes: why do astronomers use telescopes?
light gathering power and angular resolution
telescopes: what is light gathering power and what is the formula?
-greater area allows telescope to “catch” more light, it provides brighter images
- 𝐴𝑟𝑒𝑎∝𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟2
telescopes: what is angular resolution and what is the formula?
- (a”) describes the ability to resolve very fine detail and very small angles
- a”= 2.516 x10^5 9(wavelength) / D (telescope diameter)
telescopes: what does a” represent?
minimum angle that can be resolved, expressed in seconds of arc
telescopes: what is seeing?
-the distortion, or smearing, of an image caused by turbulence in Earth’s atmosphere above the telescope
⇒ Scintillation = “twinkling”
astronomical detectors: what consist of astronomical detectors?
1.) the human eye
2.) photographic plates
3.) photomultiplier tubes
4.) charged coupled devices
astronomical detectors: was the human eye the first astronomical detectors and characteristics ?
- yes, the human eye was the first astronomical detector
- characteristics
- wide dynamic range
- poor efficiency ( estimates to 1%)
- fair color response within very narrow range of wavelength
- highly subjective
- very short integration time ( estimates 0.1 to 0.2 seconds)
astronomical detectors: what are photographic plates and their characteristics?
- photochemical detectors; first used in astronomy in late 19th century
-photons striking silver molecules (emulsion) cause
chemical reactions and change opacity - characteristics
- Poor efficiency (estimates to 3% up to 10%)
- Excellent resolution
- Fair color response
- Very objective
astronomical detectors: what are the advantages and disadvantages of photographic plates?
- advantages
*ability to expose for long periods of time
*permanent, accurate, objective record of the observation - disadvantages
*suffer from reciprocity failure
astronomical detectors: what are photomultiplier tubes?
-employ a quantum mechanical principle
- the photoelectric effect; first developed
in 1907 (Joel Stebbins & F. C. Brown)
-when photons strike certain metals they liberate
electrons, which enables an electric current
⇒ The brighter the light, the greater the current
astronomical detectors: what are the advantages of photomultiplier tubes?
- excellent dynamic range
- moderate efficiency (up to 35%)
- poor color response
- very poor resolution
analysis of light: is speed of light the fastest phenomena in the universe and what is the speed of light in miles and km?
- yes
- c = 186,000 mi/s
- c = 299,792 km/s
analysis of light: what does the analysis of light reveal?
- the analysis of light reveals the physical properties of the
object or medium that is emitting or absorbing the light - note: the analysis of reflected light is very different from
the analysis of emitted or absorbed light
analysis of light: what is temperature?
-temperature: a measure of thermal energy content
-Kelvin scale (K)
-0 K =Zero energy
-K = °C + 273
analysis of light: what is Stefan-Boltzmann Law and the formula?
-Stefan-Boltzmann Law : relates the amount of energy a
body radiates to its temperature
- F(energy flux)= 5.67 x 10^5 ( Boltzmann constant) temperature ( kelvin)^4
analysis of light: what is Wien’s Law and the formula?
- Wien’s displacement law: relates wavelength of brightest emission ( wavelength max) to temperature
- wavelength max = 0.29/ t ( temperature)
analysis of light: if something is blue that means it’s temperature is?
- hotter
analysis of light: if something is red that means it’s temperature is?
- cooler
analysis of light: what is a blackbody?
-Blackbody: a hypothetical object that perfectly absorbs
all incident radiation and emits light solely according to
its temperature
- not the same thing as a black hole
-stars so not radiate exactly as a blackbody
analysis of light: what is a continuous spectrum and how is it produced?
- a continuous spectrum is a long colorful spectrum usually with no lines
- hot solids, and gasses under high pressure, produce a continuous spectrum
analysis of light: what is an emission spectrum and how is it produced?
- mainly black spectrum with thin color lines ( bright line spectrum)
- hot, low pressure, gasses seen in front of a cooler
background produce an emission spectrum
analysis of light: what is an absorption spectrum and how is it produced?
- mainly a colorful spectrum with thin black lines ( dark line spectrum)
-low pressure gasses seen in front of a hot blackbody
produce an absorption spectrum
analysis of light: does every element create a different spectrum and how?
- yes
- the pattern of spectral lines depends on the states in
which the electrons exist inside of the atoms
analysis of light: what is atomic transition?
-atomic transition: spectral lines are produced by electrons jumping between these levels
- photons absorbed or emitted by an atom have energies
that exactly match the energy differences between any
two electron energy levels
analysis of light: what type of lines does absorption spectrum produce?
- absorption lines are produced by upward transitions
analysis of light: what type of lines does an emission spectrum produce?
-emission lines are produced by downward transitions
analysis of light: what is the doppler effect?
- doppler effect: The observed wavelength of a spectral line is affected by relative motion between the source and the observer
analysis of light: what is redshift?
- redshift: when the wavelength subtracted by rest wavelength is greater than zero
- the source is receding ( decreasing or getting farther)
analysis of light: what is blueshift?
- blueshift: when the wavelength subtracted by the rest wavelength is less than zero
- the source is approaching ( increasing or getting closer)
analysis of light: what is the doppler shift?
- red and blue shift
- these shifts are called a doppler shift; they affect the
entire spectrum and allow astronomers to measure an
object’s radial velocity
analysis of light: what is radial velocity?
- radial velocity: the component of an object’s relative motion that is toward or away from the observer (i.e. parallel to the line of sight)
analysis of light: what is proper motion?
- proper motion: the component of an object’s relative motion that is toward or away from the observer (i.e. parallel to the line of sight)
stars: what is apparent magnitude?
- apparent magnitude: how bright a star (or other object) appears to an observer; is directly measurable
- 1 (bright) ⇒ 6 ( faint)
stars: what is parallax?
- parallax (pi” or p): the apparent angular shift of a “nearby” object wrt a distant background due to the observer’s own change in position
stars: what is the small angle approximation formula?
r ( distance pc)= 1/ pi” ( parallax in arc seconds)
stars: what is parsec and what does it equal?
- parsec (pc): the distance of an object with a parallax of
1 second of arc; the distance at which 1 AU subtends an
angle of 1 second of arc - 1 pc = 3.26 ly
3.1 = 10*13 km
= 20 trillion miles
stars: what is absolute magnitude and what 2 things are required to measure absolute magnitude?
- absolute magnitude: a star’s true brightness; expressed as how bright the star appears from a distance of 10 pc
- distance and apparent magnitude are needed to determine absolute magnitude
stars: what is inverse square law and formula?
- inverse square law: the intensity of light (i.e. brightness)
radiated uniformly by a point source decreases inversely
with the square of the distance - I ( intensity or brightness) ∝ 1 / r^2 ( distance)
stars: what is luminosity (L)?
- luminosity: total amount of energy radiated per second (ergs/s; or Watts); intrinsic to a star
stars: what is photometry?
- photometry: measures brightness of starlight very accurately in specific ranges of color (i.e. wavelengths)
stars: what are the categories for stars?
- blue = hot stars
- red = cool stars
- O ( hot) (2-9) mostly atoms ionized
- B (0-9)
-A (0-9) mostly hydrogen lines - F(0-9)
-G (0-9) many metal lines - K(0-9)
- M ( cool) (0-9) few atoms
stars: what two things rely on temperature?
- spectral type and luminosity
Hertzsprung-Russell (H-R) Diagram: what is the Hertzsprung-Russell (H-R) Diagram?
- c. 1911 Hertzsprung and Russell plotted stars according to
their calculated Mv and their observed spectral type - for stars known with measured parallax⇒ distance
- distance combined with apparent magnitude
Hertzsprung-Russell (H-R) Diagram: the diagram shows the relationship between what two physical properties?
- luminosity and temperature
Hertzsprung-Russell (H-R) Diagram: what is main sequence?
- main sequence: the majority of all stars adheres to this relationship; shows the most common relationship between luminosity and temperature
Hertzsprung-Russell (H-R) Diagram: what are giants?
- giants: populate only the upper right portion of the H-R diagram; commonly called red giants, cool but bright stars
Hertzsprung-Russell (H-R) Diagram: what are white dwarfs?
white dwarfs: populate the lower left portion of the H-R diagram, hot and faint stars
Hertzsprung-Russell (H-R) Diagram: what are the 5 classes of luminosity?
1.) super giants ( brightest at given spectral type )
2.) luminous giants
3.) giants
4.) sub giants
5.) main sequence ( faintest at given spectral type )
binary stars: what are binary stars?
- binary stars: two stars, gravitationally bound together, in mutual orbits around each other
binary stars: what are visual binaries?
- visual binaries: both stars can be resolved through a telescope as separate points of light
binary stars: what are spectroscopic binaries?
- spectroscopic binaries: stars are not resolved as separate points of light, but two sets of spectral lines are present, which vary over time as a result of a doppler shift
binary stars: what are eclipsing binaries?
- eclipsing binaries: when the orbit is seen nearly or exactly edge-on, eclipses are seen as the stars alternately pass in front of each other
binary stars: what do the eclipses cause?
- the eclipses cause a periodic change in the total light
received from the system; observations reveal a light curve
binary stars: what are first and second eclipses?
-primary eclipse: hotter star is eclipsed
-secondary eclipse: cooler star is eclipsed
