# Solar Luminosity

by vbillej
Tags: luminosity, solar
 P: 12 In a question is says that Brightness = Luminosity/4πr₂ (for a star). Procyon = 7L☉ and 11.41 light years as distance. the equation in B= 7L☉/ 4π(11.41)₂ the answer turned out to be 0.004 L☉ watts per square light year (its a textbook question). What i don't understand is what is 7L☉, what's its value. I read that L☉ is approx the suns luminosity so i did 7(3.839 × 10^26). but still getting the wrong answer. Thanks vbillej
P: 571
 Quote by vbillej In a question is says that Brightness = Luminosity/4πr₂ (for a star). Procyon = 7L☉ and 11.41 light years as distance. the equation in B= 7L☉/ 4π(11.41)₂ the answer turned out to be 0.004 L☉ watts per square light year (its a textbook question). What i don't understand is what is 7L☉, what's its value. I read that L☉ is approx the suns luminosity so i did 7(3.839 × 10^26). but still getting the wrong answer. Thanks vbillej
I don't exactly understand what the problem is.
 P: 12 I just don't get what 7L☉ is, i looked up L☉ but i still don't really understand how the answer was 0.004 L☉. Like how would i put 7L☉ into a calculator.
 Sci Advisor P: 2,193 Solar Luminosity L☉ is just a unit, specifically, the unit solar luminosity. Its value is defined to be the luminosity of the sun. You don't put 7L☉ into a calculator any more than you put 7 meters or 7 seconds into a calculator, you only calculate the numbers, the units are your responsibility. The equation you mentioned has units of L☉/ly^2, which is exactly what you wanted, is it not?
P: 571
 Quote by vbillej I just don't get what 7L☉ is, i looked up L☉ but i still don't really understand how the answer was 0.004 L☉. Like how would i put 7L☉ into a calculator.
$$f=\frac{L}{4\pi d^2}$$