A bright light could be seen in the sky, it divided into 2 smaller lights that moved appart.A very large round light was seen in the western sky. It was about a quarter of the size of the moon. It appeared to be quite far away. This light then split into 2 separate lights which were much smaller. One light moved below the other then moved above it. The other light slowly disappeared. Eventually the remaining light grew faint. The sky was very clear and visability excellent. Other aircaft could be seen and all had vapour trails. The bright light didn't.