Wow this was a shocker. I went out onto my balcony just before 9pm at night on Aug 9, 2016 to take pictures of nice sunset in an otherwise clear blue sky but soon long thin domes of black clouds started to appear here and there, slim in wide but a little domed in the middle. Some would fade and others appeared but no lights or anything else. Then all of a sudden I noticed these black forms forming on top of dark strips of clouds over the reddish orange clouds of the sunset and the forms almost looked like a little cityscape, like black forms of buildings. I got a picture but have to develope this film. Through a set of good binoculars they were pretty strange.I kept watching the sky because something seemed so odd about all the formations I saw so far and notice little white dots moving here and there and assumed them to be small planes over Quebec, across the river from Ottawa. I saw one of those bright white dots before, during and after the sighting of the large oval form I will tell you about next.The night was very warm and humid. I all of a sudden realized that another type of cloud was forming in the North East over the river more than over Quebec and it seemed to be in the shape of an arc, made out of white/grey clouds in an otherwise clearer blue sky in that area. The black thin clouds were in the background, not near this arc. The white cloudlike arc was just a half an arc but huge, took up half the sky it seemed and I watched it as it started to change more. From that bottom half an arc made of light whiter clouds there seemed to radiate several, maybe 5 long ray like lines that went up into what seemed like a centre of something. You still couldn't see a total form of what now looked like a huge disc but you had the feeling that the form was definitely there.Then I realized, just out of nowhere that this thing was moving. I thought ti was stationary then as I watched it I noticed that it was in fact slowly moving as a huge mass southward and over my apt building. At that point I also notice that above the white arc that made up what seemed to be the bottom of something the whole middle area was in fact much darker than the sky around it. That is when I started to freak a bit. I also notice what I think was a sort of vibrating inside me although I didn't hear that sound I felt I should have due to this sense of vibration and the size of this thing moving over my neighbourhood. I got a few pictures of it but it was so massive I couldn't get it all in the frame and again have to get these films developed.It was getting dark out but the whole event lasted about 45 minutes from the first time I noticed the whitish clouds that formed the bottom arc start to appear, they weren't there before, to when the massize object moved to the south and disappeared - moved very slowly. I honestly think that I just saw a Mothership.The way the whole centre was darker than the sunset sky around it, it all stayed in one huge shape, the oval bottom that was first to appear was out of place in the night sky with the other clouds black and disappating and then some appearing but this huge object stayed the same and appeared solid. I never saw any lights on it and the white rays I saw on it at first that went into the middle of the object slowly disappeared after a bit. For a minute in the middle of the sighting I think I saw a centre that was lighter than the rest - almost like the the whitish grey of the clouds that formed that bottom arc.Because of the heat here there were lots of air conditioners going that interfered with any sound it might have made but like I said before I am sure I felt a vibration as it went over but can't be 100% sure. I just seem to sense a deep vibration.I am a bit shaken up from this sighting because it all just seemed to form out of nowhere and before I knew it there it was and moving slowly out of sight. It was huge and you got a powerful feeling from it. I have had other sightings of various UFOs in this same area over the years, all different. Something is definitely going on in this area.I got the feeling that the majority of this huge object was cloaked or invisible in some way. None of it dissipated at all from the first I saw of it forming as that cloudlike arc. The centre was definitely much darker though like I said compared to the darker blue of the sky around it.