August 23, 2019 9:00pm (approx) i was outside watering my lawn in the dark. being a pilot for over 25 years i routinely look at the sky for aircraft, especially during the time i am watering my yard. i can see the aircraft on final for 28l/28r into kpdx as well as the flights passing overhead north/south. while looking for aircraft this particular time i saw a craft suddenly appear in the east that looked like a rocket with the engine flame out the back. the shape was very visible as well as the flame out the back, just like a rocket would look just after launch. but unlike a rocket it was traveling horizontally, perfectly horizontal with zero arch to its trajectory. this craft appeared from thin air and traveled at a high speed from south to north and much lower than the airline traffic. it also appeared to travel a perfectly horizontal path, not changing altitude, and then just suddenly disappeared. it did not get dim and fade out or get brighter, it just disappeared suddenly, just as it had appeared. the craft was large with a very bright white flame out the back and traveled very low, approximately 10-15 thousand feet above the ground. there was no sound, at least not that i could hear. the area of the sky that it appeared in was completely in my view, i just happened to be looking at that exact spot in the sky when it suddenly appeared. i followed it clearly with my eyes, it disappeared from my view momentarily behind a tree that obstructed my view. soon after it came back into my field of vision it disappeared. what i mean is it disappeared while i had an unobstructed view of it, in the same manor it had appeared, not fading or dimming, just suddenly gone.