Whats HR diagram and what does it tell us about stars?
Flux, Luminosity and Inverse Square Law Luminosity and Flux Here we review the definitions of some important quantities that we will use often in the course. Luminosity, L, is the total energy radiated from an object per second, measured in Watts. Energy flux is the flow of energy out of a surface, measured in Watts/m2. The observed flux (apparent brightness) of an object is the power we receive from it, depending on the distance to the object, measured in W/m2. We often just use the term flux without the “energy” or “observed” qualifier. The unspecified qualifier is determined by the context. Inverse Square Law How is the Observed Flux determined? Make a sphere of radius, d, around an object which is radiating power (such as the sun or a light bulb). All energy radiated from the object does not depend on the size of the sphere. However, the flow of energy per m2 passing through the sphere decreases as the size of the sphere increases. where, R = radius of the object L = luminosity of
