oval object moved horizontally across mesa, then vanishedOn Thursday, December 4th, 2008, my husband and I were walking our dog at twilight, 5pm. My husband teaches elementary school, I am a writer. Our town sits at the south foot of a 75-foot mesa in Southeast Oregon, and we often see jetliners and their contrails bisecting our skyway. On this evening we observed a smooth silver oval object flying silently along the top of the mesa. It moved at a rate slower than a weather satellite or a commercial jet, and left no contrail. We had been looking at the planet Jupiter to the southwest, and commented that this object was larger than that, with a brighter magnitude. We watched, thinking at first it was a meteor. But the object traveled horizontally and left no tail. It traveled along the mesa top approximately 300 feet at a steady rate and then vanished, disappeared into a cloudless sky.I then remembered a sighting of a similar object on Thursday morning, January 17th, '08, at 0730. This object was also a silver oval, and descended at a similar rate of speed behind another mesa to the south of our town. When I first observed this object it was approximately 300 feet above the horizon, shining like a star, but with smooth margins.I watched as it descended at a slow rate behind the southern mesa, taking about ten minutes to go behind the rim. I thought it was an odd meteor, dismissed the sight, and went about the day. At 0830 I was sitting at my kitchen table when I saw the silver object rising again from the same spot, ascend to the same altitude, and vanish from sight, disappear. The sky was cloudless; there was no wind at that time.