We were two observers, watching the start night on Lake Tahoe at 6200ft where the sky is incredibly clear without any light pollution. The object crossed the sky from NW to SE at a spectacular speed (estimated 10,000 km/h, but it's hard to tell at this very high speed), time of observation 2 to 3 seconds, the time for the object to appear into our sight vision on the left and disappear on the right. The speed looked constant, so as the direction. Estimated altitude 5000 ft from the ground. The object emitted a light at its tail when it appeared, then the light disappeared but we could distinguishably recognized a dark grey solid mass moving forward in the dark sky. No noise during the observation.