
Practice Finding and Using Angular Size
An object's angular size is approximately proportional to the object's
physical size over its distance from the observer (the approximation is
best for objects smaller than 10^{o} in size). The constant of
proportionality depends on the units you are using. For everyday objects,
we might measure the size and distance in meters, and want the angular
size in a familiar unit such as degrees. The constant you
multiply the value size/distance (if the size and distance are measured
in the same units, their ratio is in units of radians) by to get the
answer in degrees is 360/(2 pi) (360 degrees is equal to 2 pi
radians).
Here is an image of a double decker bus (like the tour buses you might
find in London or in New York City). A bus like this is about 6 meters
tall. What would its angular size be (use three significant digits) if it
were down the street from you, at a distance of 40 meters? How about if it
were several blocks away, at a distance of 100 meters?
