Astronomy 1021 Chapter Notes - Chapter 12: Inverse-Square Law, Apparent Magnitude, Photosphere

• School: Western University
• Department: Astronomy
• Course: Astronomy 1021
• Professor: Reynold Silber

Document Summary

We use the unit solar luminosity (lsun) Two stars that have the same luminosity have the same total energy output and thus are producing the same amount of energy. More energy output means intrinsically brighter stars. We can very accurately measure the apparent brightness or magnitude of stars. Further the star is, the fainter it looks. The further away a star is, the fainter it looks: apparent brightness follows an inverse square law. If you double the distance, the brightness will decrease by a factor of 4. If you increase the distance by a factor of 10, the brightness will decrease by a factor of. So a brighter star might have a higher luminosity, but it might also just happen to be closer by. Q: john reads a paper while standing 2 meter from a table that has 1 light bulb of 100 watts on it. What need distance to know the luminosity.