Calculating Luminosity from Brightness: Where Did I Go Wrong?

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SUMMARY

The discussion centers on calculating the luminosity of Gliese 581 using the equation F = (L/(4*pi*r^2)). The user initially inputs the absolute brightness of 11.6 and the distance of 1.89210568 × 10^17 meters, resulting in an incorrect luminosity of 5.21 * 10^36 watts. The correct luminosity should be approximately 6.38 * 10^24 watts. The error arises from using the absolute brightness in incorrect units, necessitating conversion to flux in watts per square meter (W/m²).

PREREQUISITES
  • Understanding of the equation for luminosity: F = (L/(4*pi*r^2))
  • Knowledge of units of measurement, specifically flux in W/m²
  • Familiarity with astronomical concepts such as absolute brightness and luminosity
  • Basic skills in unit conversion
NEXT STEPS
  • Learn how to convert absolute brightness to flux in W/m²
  • Study the implications of distance on luminosity calculations
  • Explore the properties of Gliese 581 and its significance in astronomy
  • Investigate common errors in astrophysical calculations and how to avoid them
USEFUL FOR

Astronomy students, astrophysicists, and anyone involved in stellar luminosity calculations will benefit from this discussion.

bearsfan654
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Hello,

I've been trying to solve for the luminosity of Gliese 581 using its brightness. I've been using the equation below:

WkICx65.gif


F = (L/(4*pi*r^2))

I have the flux as the absolute brightness of Gliese 581, which is 11.6. The distance, r, to the star is 1.89210568 × 10^17 meters. However, when I input all of that into the equation, I get 5.21 * 10^36 watts. That does not seem even close to the correct answer, which should be about 6.38 * 10^24 watts. What did I do wrong?
 
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bearsfan654 said:
F = (L/(4*pi*r^2)) I have the flux as the absolute brightness of Gliese 581, which is 11.6.
In which units?
bearsfan654 said:
The distance, r, to the star is 1.89210568 × 10^17 meters. However, when I input all of that into the equation, I get 5.21 * 10^36 watts. That does not seem even close to the correct answer, which should be about 6.38 * 10^24 watts. What did I do wrong?
You need F in units if W/mˇ2
How do you get that?
Because that "absolute brightness 11,6" is in different units - not W/m2.
 
How can I convert the absolute brightness of 11.6 into flux?
 

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