Estimating Limiting Magnitude
Limiting magnitude is used to evaluate the quality of observing conditions. It tells the magnitude of the faintest star visible to the unaided eye. It also quantifies the sky's transparency: better transparency means that fainter stars are visible. Limiting magnitude is used in meteor and deep-sky observing. It can be used also to approximate light pollution.
The simplest way to evaluate limiting magnitude is to find suitable stars with known magnitudes from a star map and check which of them are visible. The easier way (originally invented by meteor observers) is to count visible stars inside known star squares and triangles. A number of these areas are shown below.
Clicking on a yellow section of the map below, or on the appropriate text link at the bottom, will take to to a page with a printable star chart. These charts also have tables which show how the number of stars you can see correspond to your own personal limiting magnitude.
Click on the image map above or choose one of the links below
This information and much of the text came from Bill Arnett's
seds page on limiting magnitude,
which in turn was derived from information created by Finnish amateur
The only reason for this additional LM page is to host my
printer-friendly black on white images, all but one of which is under 30k in
All the star map images (except the image map above) were created by
Guide 8 from Project Pluto.
All the star map images (except the image map above) were created by Guide 8 from Project Pluto.