Location & time:Date: 12.08.2013. Time: approximately 11:40 - 11:55. Location of the object: southwest moving northwest moving straight over the city center of Frankfurt Germany.Location of sighting Frankfurt Germany, in the quarter Nordend.Altitude of the object: About that of an airplane (but I think it came down a little as it came toward us).Sighting:I was in my office, which has a pretty nice view of the skyline (view from the south west) of Frankfurt Germany when I noticed something I thought was a balloon flying around about 1.5 miles away. It was moving rather strange and seems to reflect the sunlight. I asked a colleague to take a look and we agreed that it was a helium balloon sparkling in the sun and continued to work (It looked like it was rising up into the air and drifting away.About 5 min later, whatever it was had come back down a little and was heading toward us (north east) I took another look at it, since it got a little closer. Now I could see a little more detail and was sure that this was no balloon. I told another colleague to come over and take a look and we both stood there looking out the window, at this strange "UFO".It was moving about the speed an airplane would move when it's up in the sky. But this object was way lower and came closer and closer. At this point I got out my Iphone 5 and did a short recording of the object, but I was a little exited and decided to quit the recording so I can see this thing with my own eyes. Now the thing was coming pretty close to our left side. At this point it was about one inch big (for us since it was no way I can tell how big it was). It was approximately the size of a small airplane. Now I had about 10 sec to view this thing as it flew over our left side. Now I was sure this was something really strange! This thing was a perfect star shape. Metallic (aluminum type) color on the inner side, while there was a white outline on the edges. I got to see this object pass over my right side. That gave me the chance to see that it was not very thick. It was almost like one of those Christmas stars you can nail to the wall (almost flat). From my distance I was about 1 inched high and about inch thick. What is even stranger is that this object was flying not like a plane or ordinary flying saucer horizontal. The star was quite flat from the side and was flying vertical!! Basically with its flat side first! How is it even possible to even fly? It was moving straight, no wobbles like a balloon, no signs of propulsion (contrail) or smoke coming from the rear like a rocket or a plane. Sadly I had to let it pass over us to our left without running to the other side of the building since I was at work and I was already making quite a fuss. I asked my colleague twice, if what we both saw was a plane or a balloon because it was just so weird and he said it was no balloon or plane, but could be a experimental drone of some sort. I asked what type of star shaped drone could fly with its wide flat side first totally straight and vertical and he replied they are here (meaning the aliens with a funny look and grin).Other colleagues laughed at me for mentioning it so I kept quiet after telling them once what we have seen. Unfortunately the video did not turn out that good since I recorded without zoom. But this object is visible flying in the sky. So at least I have a little proof.Anyway, the weird part is that I thought I saw a real balloon go up in the area where I had first seen this object (after my lunch break). But I didn't have time to investigate any further. Me my colleague are 100% sure of what we saw. A metallic object defying logic with is way of flying. It was no balloon! It was a solid (metallic craft of some unknown type).I am not sure what the other objects where because I was still shocked from sighting of craft.During the sighting I was overwhelmed with a feeling of total awe! I remember thinking how is it possible that such a thing can fly? I was so excited after the sighting that I called 2 friends in my lunch break right after the sighting to tell them about it. I was almost shaking.