I was on my balcony smoking.I saw an aeroplane in the sky and close to it what appeared to be a very very bright star I haven't noticed on other nights. After a few moments it started to fly up, not very fast and then over my head towards south-east, I think. It looked like a very bright yellow light and when it started flying I say a pulsating blue light. At first it was immobile but it still looked like pulsating, then it started to fly slowly upwards and then southwards and the blue light was more obvious. Its speed was comparable to one of an aeroplane, I reckon. When I saw it moving up I said to myself "Great God!!!". I was very excited, followed the object with my eyes and I lost sight of it as it flew over my building. I tried to spot it later in the portion of the sky viewable from my balcony, but nothing.