The "UFO" is lens flare from the street lamp in the lower right.

(Assuming one is unfamiliar, lens flares are image artifacts from the lens and sensor. In this case, a surface - probably the back of the lens - is reflecting light bouncing off the sensor back into the sensor. These are easy to identify: Draw a line from the "UFO" through the middle of the image. You will find a bright light source at a point equidistant from the middle of the image, in this case the street light.)

As a matter of fact, if you look to the upper left of the "UFO" in the sky, you can see two faint "UFO"s which are the lower two lights by the same light pole.