  We present a space-time diagram that displays in true values the space- time
coordinates of events associated with the apparent and actual positions of a
point like source moving with constant velocity. We use it in order to
construct the actual shape of a moving luminous profile or to determine the
relationship between apparent and actual distances. We show that the simple
fact that light propagates at finite speed has important consequences like
"length contraction" or "length dilation" the effects being sensitive against
the "approaching" and the "receding" character of the source relative to an
observer located at the origin of the inertial reference frame
