On monday evening, 4-9-18 at 7:20 pm mst (not dst in az) i was sitting on my front porch looking roughly north west at the clear, not quite dusk, evening sky. it was still light enough to read. a fireball appeared brightest right away like a light turning on. it had a mini tail like a newly hatched tadpole, it burned clean and pure whitish with a trace of yellow, like plasma as opposed to littered with debris of varying colors. the brightness diminished in a continuously lessening, linear fashion, then brightened at the end with one piece 10% the size of the whole, breaking off and, from my perspective, accelerating ahead of, and lower than, the main body…then click, turn the light off. it lasted 4 seconds. again from my perspective in the village of oak creek, az, it first appeared about 35 degrees above the horizon on a heading of 292. it ended about 15 degrees above the horizon at 338 degrees. it traveled in a straight line with no arc so i believe it was close yet i didn't hear a sound. thinking back, there may have been a slight arc as i got a sense that it was moving slightly away from my location. since it went from west to east and didn’t trail a debris field, i’m guessing it was space junk. i watched the area for 1 minute and no other debris appeared in my field of view.