Magnitude of Sirius?

1. Jun 6, 2017

Jussi Lundahl

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
m1-m2=-2,5*log10*(F1/F2)

3. The attempt at a solution
I have no idea what to do...

2. Jun 6, 2017

Bandersnatch

Ok, start by telling us what are the F1 and F2 in the equation.

3. Jun 6, 2017

Voltageisntreal

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

4. Jun 6, 2017

Jussi Lundahl

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.

5. Jun 6, 2017

Jussi Lundahl

Thank you! You saved my day :)

6. Jun 6, 2017

Bandersnatch

Please, do not provide full answers to questions posted in the homework forum. Spoon-feeding is against the rules.

7. Jun 6, 2017

Voltageisntreal

• Member warned not to use text-speak in posts.
;o, mb didn't kno rip

8. Jun 6, 2017

Staff: Mentor

Text speak is also not permitted!