Sirius, visually the brightest star in Earth's night sky, has an apparent magnitude of about -1.5, while the Andromeda Galaxy has an apparent magnitude of about +3.5. What is the ratio of their brightnesses, as seen by Earthbound observers?

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Quizplus · Accepted Answer

The apparent magnitude scale is logarithmic, with a difference of 5 magnitudes corresponding to a brightness ratio of 100. Sirius, at -1.5, and the Andromeda Galaxy, at +3.5, have a magnitude difference of 5, meaning Sirius is 100 times brighter than the Andromeda Galaxy.

Sirius, Visually the Brightest Star in Earth's Night Sky, Has