Astrophysics

• Rayleighs Criterion

  Two sources will be resolved if the central maximum of one diffraction pattern coincides with the first minimum of the other
• Collecting power

  Amount of light collected by aperture is proportional to diameter squared
• Luminosity

  total amount of energy emitted by a star every second
• Apparent Magnitude

  how bright a star appears to be compared to others
• Absolute Magnitude

  Brightness of a star as it would appear from a distance of 10 parsecs
• Intensity

  the power received by an observer per unit area
• Black Body

  An object that absorbs all radiation incident upon it, without reflecting or transmitting any
• Rayleigh Criterion

  minimum subtended angle between two object whose images can be resolved
• How does wavelength affect angular resolution?

  Shorter wavelengths result in better smaller angular resolution
• How does aperture affect angular resolution?

  Larger apertures result in better smaller angular resolution because they can collect more light and produce sharper images
• What is quantum efficiency?

  ratio of the number of photons falling on a device that produce a signal to the total number of photons falling on the device
• What is peak QE of the eye?

  5-10%
• What is the QE of CCDs?

  >70%
• Compare resolution between eye and CCD

  CCD have higher resolution
• Typical resolution of eye and CCD

  Eye- 100 micrometer

  CCs- 10 micrometer
• Apparent magnitude


  qualitative scale of brightness which decreases as the brightness increases
• Describe Hipparcos scale


  scale goes from 1 the brightest to 6 the dimmest
• What is the relationship for Hipparcos scale?

  from 6 going back x100^(1/5)
• What magnitude is the dimmest visible star?

  6
• Ratio of brightness


  2.51
• parsec


  distance which causes a parallax angle of 1 arcsecond to be observed
• Relationship between distance in parsecs and parallax

  d = 1/p
• Black Body Radiation Curve

  
• For BB radiation what will hottest temperature have

  shortest wavelength
• What is the relationship between temperature and intensity?

  for higher temperature, intensity is greater at every wavelength BUT it is not an equal increase
• What does it mean to have a shorter wavelength?

  greater increase in intensity at THAT wavelength
• What colour is hot peak wavelength?

  Blue
• What colour is cold peak wavelength?

  Red
• What is power proportional to?

  surface temperature ^ 4
• What is the assumption made for stars when calculating power?

  are black bodies
• Stefans Law


  $P =$$σT^4$
• Wien's displacement law


  $λ _{max} ​ T =$$2.9 × 1 0^ {− 3}   m K$
• Comparison of 2 stars to calculate ratio of diameters


  $\frac {d_1}{d_2} =$$\frac {(T_2)^2}{(T_1)^2}\sqrt{\frac{p_1}{p_2}}$
• What is meant by absorption spectrum?

  different wavelengths of energy which can be absorbed by the atom
• How is emission spectrum created?

  de-excitation

  atom emits photon
• How is absorption spectrum created?


  caused by excitation

  atom absorbs photons
• When can hydrogen absorption lines form?

  electrons need to be in n=2 state
• What can't Balmer lines do?

  give core properties as Balmer lines only give an indication of surface properties
• What does the intensity of Balmer lines depend on?

  Temperature of star
• inverse-square law


  intensity is inversely proportional to the square of the distance from the source