Terminological Confusions
In astronomy the term apparent size refers to the physical angle or angular diameter.
But in psychophysics and experimental psychology the adjective "apparent" refers to a person's subjective experience. So, "apparent size" has referred to how large an object looks, also often called its "perceived size".
Additional confusion has occurred because there are two qualitatively different "size" experiences for a viewed object. One is the perceived visual angle (or apparent visual angle) which is the subjective correlate of, also called the object's perceived or apparent angular size. The perceived visual angle is best defined as the difference between the perceived directions of the object's endpoints from oneself.
The other "size" experience is the object's perceived linear size (or apparent linear size) which is the subjective correlate of, the object's physical width or height or diameter.
Widespread use of the ambiguous terms "apparent size" and "perceived size" without specifying the units of measure has caused confusion.
Read more about this topic: Visual Angle
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