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Practice Finding Angular Size

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 10o 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).

double decker bus

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?




A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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