This photograph of 'flying saucers' over Sydney, Australia was received on 26 May 2006, and was taken from Sydney Tower.  The saucers were not visible to the photographer at the time the picture was taken.  At first glance, one might believe this photograph to be significant evidence of extraterrestrial craft flying over this large city.  Note, however, that there is a bright light in the center of the larger 'disk" at the top of the picture.  This bright light is actually a light reflection of the city lights created internally by the camera lens elements.  The light appears to dissipate, and the elliptical shape is attributed to the camera's aperture.

A complex camera lens (such as a zoom lens) will contain numerous lens elements, which can increase the likelihood for lens flares.  The additional flares are most likely attributed to multiple reflections created by several lens elements, each resulting in lens flares of varying size and appearance.  In this case, the lens flares occur in the upper half of the picture because the light source is in the lower half, although lens flares may occur above, below, or alongside the light source. 

Notice, also, that the bottom smaller lens flare is completely transparent, and the city lights can be clearly seen through it.  A strong lens flare can create a haze or an overall reduction in contrast across an entire photograph.