Brightness and Apparent Magnitude

• What is apparent magnitude defined as?

  The perceived brightness of a star from Earth
• What is the unit of apparent magnitude?

  It has no unit
• What is apparent magnitude?

  The perceived brightness of a star as seen from Earth
• What is the range of the Hipparcos scale of apparent magnitude?

  1.0 to 6.0
• What does the Hipparcos scale of apparent magnitude represent?

  Brightness of stars that can be seen with the naked eye

  
• What is the relationship between a change of 1 order of magnitude in apparent magnitude and the change in brightness?

  Magnitude decreases by 1, brightness increases by a factor of 100$\frac{1}{5}$ ≈ 2.51

  
• If the apparent magnitude of object A is 3 and the apparent magnitude of object B is 6, what is the ratio of their intensities?

  $\frac{I_A}{I_B} =$$2.51^{(6-3)} =$$2.51^3 =$$15.85$
• What is the relationship between apparent magnitude and brightness?

  The more negative the apparent magnitude, the brighter an object appears. The more positive the apparent magnitude, the fainter an object appears.

  
• What is the faintest object that can be detected by the naked eye?

  Magnitude +6
• What is the faintest object that can be detected by the Hubble Space Telescope?

  Magnitude +31
• If the faintest object detected by the Hubble Space Telescope is magnitude +31 and the faintest object detected by the naked eye is magnitude +6, what is the ratio of their brightness?

  $\frac{I_{Hubble}}{I_{Naked Eye}} =$$2.51^{(31-6)} =$$2.51^{25} \approx 10^7$
• What are the apparent magnitudes of common astronomical objects?

  • Sun: -26
  • Venus: -4
  • Polaris: +2
  • Pluto: +15

  
• How do the stars in the Centaurus constellation appear to a naked-eye observer on Earth?

  • Alpha Centauri A and B appear as a single star
  • Beta Centauri Aa, Ab, and B appear as a single star
  • Proxima Centauri is not visible to the naked eye
  • Alpha Centauri AB appears 2.25 times brighter than Beta Centauri

  
• What is the ratio of brightness between Alpha Centauri AB and Beta Centauri?

  $\frac{I_{Alpha Centauri AB}}{I_{Beta Centauri}} =$$2.51^{(0.61 - (-0.27)} =$$2.51^{0.88} \approx 2.25$
• What is the formula to compare the brightness of two objects A and B?

  $\frac{I_A}{I_B} =$$2.51^{(m_B - m_A)}$
• How does the brightness comparison formula relate to the change in apparent magnitude?

  A change of 1 order of magnitude in apparent magnitude corresponds to a change in brightness by a factor of 2.51
• What is the Hipparcos scale of apparent magnitude?

  A logarithmic scale that classifies the brightness of stars from 1.0 (brightest) to 6.0 (dimmest)
• Why is the Hipparcos scale of apparent magnitude a logarithmic scale?

  To allow stars to be compared meaningfully in terms of their brightness or intensity

  
• What is the relationship between a change of 1 order of magnitude in apparent magnitude and the change in brightness?

  Magnitude decreases by 1, brightness increases by a factor of 100$\frac{1}{5}$ ≈ 2.51

  
• If the apparent magnitude of object A is 2 and the apparent magnitude of object B is 5, what is the ratio of their intensities?

  $\frac{I_A}{I_B} =$$2.51^{(5-2)} =$$2.51^3 =$$15.85$
• How does the brightness comparison formula relate to the Hipparcos scale of apparent magnitude?

  The formula allows you to quantify the difference in brightness between objects with different apparent magnitudes

  
• What is the resolution limit of the naked eye?

  Magnitude +6
• What is the resolution limit of the Hubble Space Telescope?

  Magnitude +31

  
• How much dimmer is the faintest object detectable by the Hubble Space Telescope compared to the faintest object detectable by the naked eye?

  The faintest object detectable by the Hubble Space Telescope is approximately 10^7 times dimmer than the faintest object detectable by the naked eye