Difficulties in using the magnitude scale in Observational Astronomy

Q: Why is it difficult to understand the magnitude scale system?

Stars drawn to magnitude in a star chart

A: It works backwards with brighter objects having smaller and negative values. Also each magnitude difference gives a brightness difference of 2.5. For instance, a star with a magnitude of 4 is 2.5 times brighter than a star with magnitude 5. And when there is a difference of 5 magnitudes, the brightness difference is about  100 times (2.5 X 2.5 X 2.5 X 2.5 X 2.5 = 97.7)

There is advantage of using the system. It compresses the scale so a wide range of brightnesses can be represented by a close range of numbers.

In a quiz, you can be asked of the magnitude values of well known objects. Though planets’ magnitudes change depending on the position and distance,  it’s useful to remember their average values.

Sun                        -26.7

Moon                    -12.6 (full moon)

Venus                   -4.7 (brightest)

Mars                      -2.9 (Brightest)

Jupiter                  -2.8

Mercury               -1.9 (Brightest)

Saturn                   0.7

Uranus                 5.5

Sirius                     -1.4

Canopus              -0.7

Polaris                   1.9