One of the peculiar aspects of Einstein's theory of special relativity is that the length of objects moving at relativistic speeds undergoes a contraction along the dimension of motion. An observer at rest (relative to the moving object) would observe the moving object to be shorter in length. That is to say, that an object at rest might be measured to be 200 feet long; yet the same object when moving at relativistic speeds relative to the observer/measurer would have a measured length which is less than 200 ft. This phenomenon is not due to actual errors in measurement or faulty observations. The object is actually contracted in length as seen from the stationary reference frame. The amount of contraction of the object is dependent upon the object's speed relative to the observer.
We need to note that length contraction is only significant when the object is moving at relativistic speeds - i.e., speeds which are a significant fraction of the speed of light. Furthermore, note that the contraction only occurs in the dimension of the object's motion. If the object is moving horizontally, then it is the horizontal dimension which is contracted; there would be no contraction of the height of the object.
Figure 1: Observed length of an object at rest and at different speeds
(This link is a great example to length contraction):
I believe that length contraction is an optical illusion that is a direct consequence of special relativity. It is negligible at everyday speeds and can be ignored for all regular purposes. It could cause objects moving at speeds close to the speed of light to view their lengths differently than what they actually are. A lot of satellites, radar systems and image processing software is being calibrated to account for length contraction so that we can correctly estimate the dimensions of objects in outer space that are moving at a substantial fraction of the speed of light.
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