Astrophysics

• Luminosity

  Total energy emitted as EM radiation per second
• Luminosity/ Power output units

  Watts
• Brightness aka Intensity
• Brightness/Intensity


  A measure of the power per unit area
• Apparent Magnitude


  The brightness of an object from Earth
• What kind of scale is the Hipparchus Scale?

  Logarithmic scale (2.51)
• Apparent Magnitude: the lower the number...

  The brighter the star
• Intensity Equation 


  I=P/4πr^2
• Absolute Magnitude


  The brightness of an object as it would appear at a distance of 10pc from Earth
• Magnitude Equation 


  m-M=5log(d/10)
• Astronomical Unit (AU)


  The average distance between the Sun and the Earth
• 1AU 


  1.5x10^11
• Light Year


  The distance travelled by light in a year
• 1ly


  9.46x10^15
• Parsec


  The distance when the angle of parallax is 1 arc second
• 1 arcsecond


  1/3600 degrees
• Black Body


  A body that absorbs all electromagnetic radiation of all wavelengths and can emit all wavelengths of electromagnetic radiation
• Black Body Curves


  The peak of the curve moves towards the shorter wavelengths as temperature increases
• Wien's Law


  The temperature of a star is inversely proportional to the wavelength of EM radiation emitted
• Wien's Constant


  2.9x10^-3
• Stefan's Law 


  The power output of a star is proportional to the fourth power of the stars surface temperature and is directly proportional to the surface area
• Wein's Law equation


  λmaxT=2.9x10^-3
• Stefan's Law equation


  P=σAT^4
• Inverse Square Law Assumptions

  • The star is spherical
  • It gives out an even amount of power in every direction
• Hydrogen Balmer Lines


  The balmer lines are seen in stellar spectra where light emitted by the star has been absorbed by Hydrogen atoms in the stellar atmosphere
• What properties does the spectral classification ignore?

  • Absolute magnitude
  • Apparent magnitude
  • Distance
• Spectral Classes


  O, B, A, F, G, K, M
• What temperature is class: O?

  25000-50000K
• What temperature is class: B?

  11000-25000K
• What temperature is class: A?

  7500-11000K
• What temperature is class: F?

  6000-7500K
• What temperature is class: G?

  5000-6000K
• What temperature is class: K?

  3500-5000
• What temperature is class: M?

  <3500K
• What colour is class: O?

  Blue
• What colour is class: B?

  Blue
• What colour is class: A?


  Blue/White
• What colour is class: F?

  White
• What colour is class: G?

  Yellow/White
• What colour is class: K?

  Orange