Luminous oval in evening sky over Madison, SD.At approximately 8:40 I observed a UFO in the western sky, as high as the clouds but not close enough to figure out size, exact distance away not known. Could not be a cloud because it was completely luminous. The sun was blocked out by a few clouds on the horizon.No visible exhaust trails. Oval shaped. Color was white. I do not know when it exactly appeared, but from my observation the sighting lasted about two minutes. It moved so slowly it was hard to tell it was moving, and at one point it just faded into the sky. I saw it for a minute and brought three others to its attention. All three and I are young and related. I have interest in UFOs already, the second witness has a little less, the third has some minor interest, and fourth hardly at all. Could possibly be some odd reflection of the sun, I doubt it was our imagination.