I was looking at what i thought was a faint star in the sky when i noticed it moving. i thought it was a plane at first but there were no apparent blinking lights (it was just getting dark and the stars were becoming visible in my backyard). then it turned 90 degrees very quickly, and began accelerating very rapidly (far to fast to me a commercial jet). then it either accelerated to a position beyond my field of view, or became to fain to see; i'm not sure which. i can't say for sure it was a ufo, but it behaved in a manner i never saw before.