given
Nickel diameter d= 21 mm = 21*10^-3 m
We know that two round or spherical objects have the
same angular diameter, even though they are at different distances
from the oswerver.
  they have same angular size, that is d/l
nickel = D/L moon
  D diameter of moon = 3474*10^3 m, L distance
from moon to earth = 3.84*10^8 m
       d diameter of nickel =
21*10^-3 m, l=?
     D/L =
d/l    ==>  l = d*L/D ,
          l=
(21*10^-3*3.84*10^8)/3474*10^3
                                   Â
l = 2.3212 m
nickel must be held so that it has the same apparent size
as the moon is 2.3212 m from eye.
