Limiting Magnitude

The limiting magnitude equation tells us the highest magnitude object that can be resolved by a certain telescope of diameter D[mm].

Limiting Magnitude = 2 + 5log( D_scope )

Example:
Using the same 130 mm diameter as in the example before, the highest magnitude object observable is 12.57 magnitudes.

Limiting Magnitude = 2 + 5log( 130 mm ) = 12.57

So a star with magnitude greater than 12.57 (i.e. magnitude 13.00) would not be visible with this telescope in ideal seeing conditions. It is useful to note that the magnitude scale is backwards from what one might instinctively think. Greater magnitudes result in a dimmer object, while lesser magnitudes are brighter objects.

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