I'll start off by mentioning this occurred sometime between 6:45 - 7:00 p.M. (1/7/18) lasting for 30 - 45 seconds, and it's currently 7:00 a.M. the next morning (1/8/18). the sighting occurred roughly 12 hours ago. the temperature was around 40 degrees fahrenheit, and there was a mild breeze. the weather was overcast: the clouds were low and completely filled the sky. the sky was slightly brighter than usual because of this, but not much. due to the amount of cloud cover, the stars were not visible whatsoever. my sister and i were outside our house taking a quick smoke break (cigarette) to relieve our studies (we're both college students). i noticed a green light stretching horizontally in the distance across the night sky, but this was emitting from a tall building less than five miles away. this building is covered in green lights, and come nighttime it turns on and basically becomes a gigantic green light bulb. the clouds were low and this is a building over 30 stories high, so the light was illuminating the sky above it. the clouds were above the building, but they weren't more than 200 ft. above it i would presume. our house is on a corner lot with two streets intersecting at the northeast corner (one running along the north side; one running along the east side). we were watching from the backyard which is on the south side of the house, and we were facing west (the location of the light). we were just talking as we looked up at the green light. we kept looking at it because honestly we hadn't seen it before. it was a night consisting of weather/cloud coverage that isn't typical in the memphis area. after a minute or so, i saw this dark figure seemingly emerge out of nowhere above the green light. my sister doesn't have great eyesight, but mine is 20/20. i knew just from the sheer size of it that it wasn't anything man made, so i pointed it out to my sister and asked if she saw it. even with her sub-par eyesight, she saw it immediately. it remained behind the clouds, but the light emitted from the building and into the clouds resulted in the ufo being exposed for a brief moment. the craft did not reflect any light. the craft might have come from the left side of the light or simply farther behind it, and perhaps i just couldn't see it until it was right above the green light. from my perspective, though, it looked as though it just materialized out of thin air within a couple of seconds. it was an oval-shaped, disk-like shadow sticking out like a sore thumb in the sky. when i say it was oval-shaped, it was, but the outer edges of the craft were thinner and it was thicker in the middle (i'll draw a picture of it make sure the shape is understood). it seemed to slightly descend when it first came into view, but then it stopped and remained stationary for a couple of seconds. slowly thereafter, it made its way across the sky - starting above and slightly to the right of the light, and proceeding to travel northeast away from it. it seemed to be traveling in a straight line, but it did appear to have an extremely minor downward tilt. if going in a straight line is considered 180 degrees, it was at 175. it was much larger than any sort of airplane or aircraft that i'm aware of by a long shot. it didn't make any noise, at least from where we were (probably 5-7 miles away). across the street that runs along the north side of the house, there is an abundance of tall trees in the front yards of the properties. the craft was at an altitude low enough for me to know that as soon as it got to the tree line, we wouldn't be able to maintain visualization with it. starting when the craft appeared, it only took about 30-45 seconds for it to drift out of site. throughout the experience, i had an enormous rush of adrenaline rushing through me. it wasn't because i was afraid, but rather a result of seeing something i had never seen before. i've always suspected the possibility of ufos to be more likely than not, given the amount of sightings each year, but this left me without a doubt in my mind that they exist. unfortunately, we didn't take a video which is something i never thought i would forget in an event like this, but my sister and i were both basically in shock while watching this. when i realized it was about to be out of sight, i snapped out of it and told my sister to record it, but she didn't get it in time. she got a photograph of the sky that shows the low hanging clouds and the green light, but the ufo in reference was behind the trees before she got the picture off. there is an odd-looking gray mass in the photo, but i'm not sure what that is. we didn't notice it until we looked at the photo. using the photo as a reference, though, i can say very confidently that what we saw was many shades darker.