2 moving lights

Walking the dog, about 11pm, while he stopped I was watching aircraft pass overhead west to east, on approach to a major airport.
The night was completely clear with no moon, the sky looking very very black, showing an unusual amount of stars for a city skyline.
While turning back toward the west to catch sight of the next plane, 2 lights caught my attention.
 They seemed to be quite low in the sky, much lower even than the aircraft on approach about 12 miles from the airport.
They seemingly followed the same path as the aircraft that had just gone ahead of it.
There was absolutely no sound, which was strange, but what was stranger… The 2 lights were not overly bright, no brighter than the brightest stars visible, but as they traveled east, they moved toward and away from each other.
At the outermost part of the cycle, the lights were about 35 to 40 feet apart, from the ground they came apart a distance that seemed a bit wider than the houses they flew over.
At the innermost part or cycle they would almost touch.
A complete cycle I would guess at maybe 3 seconds.
I saw this for a total of about 6 or 7 seconds.
 The path the 2 lights took toward and away from each other was perfectly straight, almost as they were moving from wingtip to body center and back.
But there was no wings or body, there were no stars blocked out as it traveled; there was no shape or outline of any kind.
 I was surprised once more when it  disappeared right after it seemed to pass over the nearest house to me,, emphasizing how low it was.
 The speed was fast enough that it would have been visible across the sky, from west to east, for no more than 10 or 12 seconds.
Source of report indicates that date of the event is approximate.  PD