large elongated triangle configuration of three lights in erratic movement over Nauset Light Beach 8-9 pmI went to Nauset Light Beach in Eastham, MA, on Cape Cod last night, August 18, 2015, with four other family members. We have a family home there and are well familiar with the area for more than 40 years. We arrived on the beach probably about 7:45 or 8 pm not too long after sunset. No one in our party had consumed anything intoxicating. The sky was still somewhat bright and just beginning to darken. I lay down on the sand and looked up to search for the first visible star, which I quickly noticed was almost directly overhead. There were almost no other stars out yet, so I was just mindlessly looking at this one. At first I noticed that it seemed to be moving but slowly, not at the rate you would expect for a plane at that height. So then I thought "oh that is not a star perhaps a satelite". To my knowledge I have never (knowingly) seen a satelite before so I took more interest in watching it. It was then that I realized that periodically--perhaps every three or four minutes but not according to any specific regular interval--the movements were nothing like how a plane would move in the sky, they were erratic, zig zag, the light would become still and then shoot forward a short distance, now left, now right.It was strange and intriguing but not alarming to watch this, and it made absolutely no sense to me at all so I called to my 17 year old nephew to give me a reality check (ie, tell me I was nuts and there was nothing strange happening in the sky). He started watching too and almost immediately saw the same strange things. It was a few minutes before we realized that we were actually watching two different lights, and that there was also a third and together they formed an elongated triangle.The three lights seemed to remain equidistant and never broke the elongated triangular shape. I cannot properly estimate the area the shape occupied as it was over our heads I would guess it the size of a large parking lot. Although the light moved around, the area they encompassed always remained directly over our heads--so that despite the erratic and unexpected movements we seemed to observe, they stayed in the same general area the entire time.My sister looked up briefly and told me it was my imagination and that "if you stare at any star long enough it appears to be moving". I am certainly familiar with the general phenomenon she referred to, but what we saw was nothing like this. My nephew and I watched intently for about 30 minutes, and we were on the beach for about an hour all together. The lights would be still and then jerk suddenly in one direction or another left or right or zig zag etc and we would call to each other "Holy crap, did you just see that?" etc. Those exclamations probably happened at least 10 times, and my sister even scolded us for using colorful language becase we didn't actually say Holy Crap and there were children elsewhere on the beach.The night was windy but not overtly so. I did consider if what we say could have been a drone at night, I have only ever seen them during the day but I could not account for how three of them would be able to maintain the shape or what appeared to be orchestrated movement between them--the wind was sufficiently strong coming off of the water and the presumed height of the object, if indeed there was one--that I would think it extremely difficult for a manually operated drone to maintain its general position in the sky let alone maintain a large shape in formation with other manually operated objects, but that would be the most logical explanation. At no time did I ever see a hard outline to the shape, or a surface, or anything else like that. Just the three lights moving in very unexpected ways such as I have never seen any other lights move in the night sky. But nor did I ever see other stars or any light inside the triangular area (which could be one indicator of whethe! r there was a large object occupying the space between the three lights),although the stars were still just coming out so there is every possibility none were yet visible in that area to the naked eye.At times there seemed to be smaller VERY faint lights moving to the to the 'edge' of the area and disappear, but this could have been an optical illusion of the sort my sister had previously described, but they seemed to disperse aight or air around them when they reached the edge of the triangluar space and then were no longer visible. They did not appear to be aircraft of any kind. Soon two planes (I assume) flew very near to the object, neither interacted with it and both seemed to travel in a straight flight path that not change as they approached the triangular area, and neither plane transversed the triangular area. The second plane had a number of bright flashing lights on it of different colors--my nephew said aloud what I was thinking that that plane had very odd lighting on it--look there were too many lights on it and they flashed a lot more than you would expect, the night sky was very clear with little to no clouds. Since my curiosity was somewhat aroused by ! this point I did consider if at least the second plane was there for some observational purpose. I did not and do not want to make more of the 'incident' than what is was--something that seemed very unexpected and somewhat strange. My cellphone battery charge was as always this vacation nearly worn down but I don't think that photographing it would have been of any use and I sincerely doubt that the my camera on phone could pick up starlight at that distance, though I've honestly never tried. At some point I think my sister became alarmed that I was perhaps exciting my nephew and so she called for us to drive back to the house. I should note that there were a number of other people on the beach, there were three bonfires blazing, and no one else appeared to notice anything, nor did we attempt to involve anyone and see if they saw what we saw--that seemed pointless. You would have to be looking closely and intently to have noticed anything out of the ordinary at all. As we left the sky was now bright with stars, and the lights were still visible. Nothing distinguished the lights in question from 'stars' except for the intermittent but very erratic movements and that they seemed clearly linked somehow in an elongated triangle shape (for lack of a more descriptive term). After we left we stopped at Ben and Jerry's for ice cream and did not get back to the house until perhaps 10 o'clock. We did not attempt to sight the lights again so I do not know if they were still there. When we got back to the house I did check myself by staring at the stars intently for a while to test my sister's theory that it was just an optical illusion but at no point did any visible light make any unexpected movement, or do anything other than 'twinkle' in the usual way, and the night was very bright with stars by then as this is a low-light area at night. We had gone to the beach last night to enjoy the air, see some seals (there are tons of them on that beach now) and hopefully see a remnant of the August meteor showers that we have watched on that beach since childhood. I am sure that this description I have written is very mild and boring compared to others you receive and most likely it is easily explainable by known phenomena. It really doesn't make sense that an object large enough to cover that area would not be more visible, would not be seen by other people, and that it would appear in such a relatively populous area. Also my sister and her husband and my niece said quite clearly that they did not see anything that alarmed or intrigued them, so in truth the majority of our party of five did not see what me and my nephew saw. But my nephew and I were both sufficiently startled by what we saw at the time. In the end I cannot escape the fact that I saw something that I cannot explain in the night sky, and it left me feeling slightly bewildered and slightly shocked as it happened. I make no claim other than the fact that what I saw was inexplicable to me.