Looking at the sky at night, sometimes you will see crescent clouds, like darts, which are very fast. What could it be? There is no sound, so it can be seen that it is not an airplane.

I used to take pictures on the mountain alone, and I found something the size of the moon moving suddenly and quickly, and then it was a few hours. It's definitely not a drone or something, because it's fast and far away, and it's not the speed of an ordinary plane, much faster than that of an ordinary plane!