Almost translucent sphere travelling at high speed/altitude across Santa Cruz, CA during the day.I was lying on Santa Cruz beach, approx. 50 meters east of the main pier/wharf.I spotted a light in the sky and I watched it thinking it was an airoplane, as there are many commercial flights whose path is almost directly above the beach. These planes are usually travelling in a northerly direction, heading for San Jose airport.However the object I watched was travelling extremely fast and made no sound. It moved in an exactly straight line from east to west. To help describe the speed, imagine lying on your back with your feet pointing south, hands pointing out and the sky above is one half of a clock face: your left hand is east and also 12 o'clock; the right hand is west and 6 o'clock. I spotted the object at around 1 o'clock and watched it travel until 5 o'clock in less than 5 seconds.As the object moved it was completely silent and left no trails. It appeared to go through brightness changes, as if light was being internally reflected off the inside of a sphere. The brightness changes were as linear as the object's motion.I have watched many planes over the skies here and this was not a plane (well, not a normal one anyway).