diff --git a/content/physics/thermodynamics.md b/content/physics/thermodynamics.md
index de6c9f1..b97e523 100644
--- a/content/physics/thermodynamics.md
+++ b/content/physics/thermodynamics.md
@@ -104,3 +104,13 @@ $$
 This is where the Boltzmann law comes in to play. In order to calculate the emissivity of an object, you first need bot: the power of emissions from the target object, and the Power that would be emitted by a black body of the same temperature. This value can be procured using the Stefan Boltzmann Law of Radiation. 
 
 Albedo, however, is a far simpler quantity, relying only on the input and output energies of the object.
+
+## Inverse Square Law and Apparent brightness
+
+If $b$ is the Power experienced at a radius $r$:
+
+$$
+b=\frac{L}{4\pi r^2}
+$$
+
+The above is true when $L$ is procured from the source, most likely using the Boltzmann's law.