Where is the remote?
Just thinking loudly .... may be the change in effective "angle of view" comes into consideration?Arshad bhai, I am not sure if I agree to what you said. I have searched numerous threads on web that confirm your claim though.
According to my understanding, angular movement of star is same no matter what is the sensor size (pixel density being same)
A crop sensor camera is showing you a smaller portion of the image of what would be captured by full frame sensor, so technically angular movement of stars should be same for both formats.
hence no need to use the "crop ratio" in "rule of 500"