 The two key jet features we observe directly are its apparent luminosity and its apparent motion across the sky. A study done by a team of astronomers using the European very long baseline interferometer radio telescope network analyzed the motion of one of the knots near the jet's origin at the black hole. They found that one of the components moved 30 mAh over two years. That's a very tiny amount, but when you multiply it by the large distance to m87, we find that the distance traveled was eight light years. To travel eight light years in just two years means its velocity is four times the speed of light. We call the apparent velocities greater than the speed of light superluminal motion. Here's how it works. Suppose we have an object at location A at time t1. That moves to location B at time t2, the travel time being delta t. D is the distance traveled. It will equal the object's velocity times its travel time. We're observing this motion from a great distance at an angle theta from the object's line of motion. We see only the proper or transverse motion across the sky, designated here as d prime. Our start time is the object's start time, plus the time it takes the light to get from point A to point O, where we are. Our end time is the object's end time, plus the time it takes the light to get from point B to point O. With that, we can calculate the observer's view of the object's velocity in terms of the object's view and vice versa. If we plug in the numbers we found for not C in the M87 jet, we find that the apparent velocity of four times the speed of light turns out to be 0.97 times the speed of light in the object's frame of reference. And the apparent elapsed time of two years turns out to have taken the object almost 67 years. It was not traveling faster than the speed of light. Note that this only happens when the velocity of the object is near the speed of light, and in addition, the viewing angle is small.