My wife and I were enjoying our rented hot tub around 11:30pm to midnight. We had observed several meteors and airliners. The sky was very clear and there was little ambient light in the area.I noticed these two star-like lights flashing erraticly but moving at a very steady spead and heading from the SW to the NE. The distance between the lights did not change a bit leading us to conclude they belonged to a single vehicle. We tried to see if stars were blocked out by it's passage but it's flight path didn't take it in front of any bright stars and it was very difficult to tell. Altitude was very difficult to tell, but I would estimate that it would be roughly half the altitude of an airliner, which we see regularly in the sky from our backyard. So roughly 15000 to 18000 feet.The entire sighting lasted about 2 or 3 minutes. These were not any kind of aircraft lights that I have ever seen.