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Homework Help: Magnitude of Sirius?

  1. Jun 6, 2017 #1
    1. The problem statement, all variables and given/known data
    Stars are observed through a triple window.
    Each surface reflects away 15% of the incident light.
    a) What is the magnitude of Sirius (m = -1.5) seen
    through the window?

    And I know that the solution is -0,97.

    2. Relevant equations

    3. The attempt at a solution
    I have no idea what to do...
  2. jcsd
  3. Jun 6, 2017 #2


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    Gold Member

    Ok, start by telling us what are the F1 and F2 in the equation.
  4. Jun 6, 2017 #3
    If 15% is deflected each time, then sirius's intensity, which let's say is 1 becomes 0.614 since (0.85)^3=0.614

    Then, log(1/0.614)*2.5=0.5295

    0.5295 is hence the difference between the apparnt magnitudes of the star after it has passed through the three windows. -1.5+0.5295=-0.9704

    There's the answer.
  5. Jun 6, 2017 #4
    I think those are called flux density in English. $$F=\frac{L}{4 \pi r^2}$$, where the L is luminosity and r is radius. $$ L= \omega r^2$$ where $$\omega$$ is solid angle?? and r is radius.
  6. Jun 6, 2017 #5
    Thank you! You saved my day :)
  7. Jun 6, 2017 #6


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    Please, do not provide full answers to questions posted in the homework forum. Spoon-feeding is against the rules.
  8. Jun 6, 2017 #7
    • Member warned not to use text-speak in posts.
    ;o, mb didn't kno rip
  9. Jun 6, 2017 #8


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    Staff: Mentor

    Text speak is also not permitted!
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