We have seen several similar sightings in and near Harrisburg in the last year. We refer to them as the "strobe light" clouds. They last approx. 40 minutes and then fade away. We also heard a noise something like a distant train. From our viewing position, no ground base light could ever be pin-pointed and we looked hard trying to locate a point of origin for the light waves. The waves of lights seemed to materialize high in the sky and move in an "ocean tidal manner" that is one wave after another, each new wave washing over and dissipating the former one...... approximately every 8 counts. The pattern starts in the North-East quadrant and slowly moves to the South-West quadrant, but the whole light wave "pattern" (which takes up one forth of the sky) moves across the sky as a total unit horizontal to us on the ground (like a flat ceiling above us) until finally out of sight. There never was a time when we were watching that the light wave simply blinked out (as if a ground light had been turned off). We live in an area where there are no businesses that would be advertising with a strobe light, it would have to be coming from Columbia which I doubt we would even be able to see from Harrisburg. And even if it was an advertising strobe, why just for 40 minutes? I mean those big strobe lights are awkward and clumsy to move....if you're really serious about advertising something or "drawing people in" why not leave them on long enough for people to find you.......like maybe 60 minutes, or better yet, 2 hours.