This UFO sighting occurred in the 4 year interval starting mid year 1952 to mid year 1956.
I was 16 to 20 years old at the time, I am now 73.
The observation occurred in Pasadena, CA.
My mother was working in her garden behind our house in mid afternoon on a beautiful sunny day.
There were no clouds, the sky was blue, and there were no winds.
She called me to come out of the house because there was something in the sky she wanted me to see.
Her voice was urgent.
According to my mother, now deceased, the UFO was heading South, made a 90° left hand turn and then was headed East.
When I came out, it was headed East.
The object was incandescent white, like a light bulb, and had a perfectly circular cross section.
There was no exhaust of any kind or any vapor trail.
It was completely silent.
The object was flying very close to a jet aircraft.
After 50+ years, I'm not completely sure of the following, but I believe that the object was trailing the jet aircraft to its right.
I could see very clearly the swept wings of the jet aircraft, one jet engine under each wing, the 2 horizontal tail stabilizers, and the fuselage.
When jets fly at 35,000', you can hardly see them.
This one was much closer, possibly 10,000' to 15,000'.
If you placed that circular object on top of the jet, I believe it would be just large enough to cover up the jet.
Since the direction and distance from the jet to the UFO did not change, I believe both were at the same altitude.
As the UFO was travelling toward the eastward horizon, it ejected a smaller version of itself, maybe ¼of the diameter, incandescent white, circular cross section, to the South.
It moved South through a 30° to 45° arc in about 3 seconds.
It stopped at this point and just faded away.
Possibly because it was moving radially away from me.
The jet and the main UFO continued until they disappeared over the eastern horizon.
I have never seen anything like this UFO.
It was either from this Earth or it was not, I wish I knew.