Why can't you shoot the orbits of stars from seven to seventeen with a SLR?

I chose the first day to the fifth day, and I avoided the moonlight from the 23rd to 30th of the lunar calendar. Otherwise, the night sky is clear, the moon and stars are scarce, and no stars can be photographed.

Pay attention to the weather forecast and choose cloudless days in Wan Li. Stay quietly for a few minutes in the dark night to adjust your eyes. Look up at the sky, find the Big Dipper, and find the position of the North Star according to the Big Dipper. Point the camera at Polaris and use door B.

Only when the exposure time exceeds half an hour can you see the obvious star shift.