I was backpacking with a group of high schoolers in the Yosemite backcountry during the first week of July, 1987. I was a chaperone. We hiked from Tuolomne Meadows up to Young Lakes and made camp at the first lake at approximately 37���56'16.47" N 119���20'51.91" W (view photo on Google Earth). At sometime around 10pm the students and the other chaperones were doing a group massage exercise. I had a slight case of altitude sickness and was away from the group lying on my back looking East at the sky. About a half hour later, along the ridge of the mountains, a very bright white light appeared from behind and slightly to the right of a peak on the ridge (see aforementioned Google photo at the leftmost peak near the trees). It was too large and too bright to be a star. At first, I thought it was an aircraft. But there was no sound and only the single light���no running lights. It was also too big to be a spotlight from a helicopter. As I recall, it appeared to be roughly the size of a pea at arms length from my perspective.It rose slowly at first, but as it ascended it picked up speed until it seemed to accelerate exponentially. It had a vertical trajectory. It continued to rise until it was as faint as a dim star, and then, quickly vanished.The event happened so fast and I was so transfixed, I was unable to tell anyone while it was happening. Also, the group was too far away and the exercise in which they were engaged required silence. None of them were looking up due to the nature of the exercise. And, of course, when I explained what I had witnessed to them about an hour later, I was met with disbelief. The next day, we hiked back down to Tuolomne Meadows Village. I was among the first of the group to arrive and was hanging out in front of the store when one of the students I told the night before came rushing over to me. She had met a group of hikers along the trail who were camping on the opposite side of the ridge nearly due East from our camp site. She was the first person they ran into on the trail; and immediately upon meeting her they said, "You won't believe what we saw last night!" She introduced us and we shared notes.Their story was much more remarkable than mine. They had been camping next to the lake that feeds Delaney Creek (37���55'54.85" N 119���18'18.13" W) the night before. They built a makeshift sweat lodge from fallen branches during the day and were enjoying their creation that evening when suddenly, they noticed a bright light coming from the direction of the lake beaming through the holes of their lodge.From what I can recall from what they told me: when they peered out of the entrance of the sweat lodge, they saw a large spherical object that was hovering above the surface of the lake. They told me all they could see was bright light. They said it made no sound. Then, a beam of light from the object scanned their camp site and soon pointed directly at them. They retreated back into the lodge until the beam went away. After that, they peeked out at the object and said it began to rise vertically and the rest of their description matched mine exactly save the fact that it was from the other side of the ridge.