<PRE><B>Question 561805</B>
An optical instrument is required to observe stars beyond the sixth magnitude, the limit of ordinary vision, however, even optical instruments have their limitations. The limiting magnitude L of an optical telescope with lens diameter D (in inches) is given by
L  = 8.8 + 5.1logD
:
a) Find the limiting magnitude for a homemade 6-inch reflecting telescope.
:
Just replace D with 6 and solve it
L = 8.8 + 5.1*log(6)
L = 8.8 + 5.1 * .778
L = 8.8 + 3.968857
L = 12.8 limiting magnitude</PRE>