the earth rotates from west to east around its axis in slightly less than 24 hours. the celestial sphere and all objects on it appear to rotate from east to west around the celestial poles in the same time. this is the diurnal motion ("daily motion"). this is why stars will rise in the east and set in the west, (unless a star is circumpolar). on the next night a particular star will rise again, but with our normal clocks running a 24-hour 0-minute cycle, it will do so slightly less than 4 minutes earlier. by the following night the difference will be 8 minutes, and so forth with every following night (or day).