The NCP would lie at the north point on your horizon. But, if you were alongside the observer at latitude 40 degrees North, the NCP would be at 40 degrees above the north point on your horizon. From these observations one can conclude that in general the NCP s angular distance above the north point on the horizon is always equal to the observer s latitude. For example, if you measured this angle to be 53 degrees you would be standing on the Earth's surface at a latitude of 53 degrees North. The daily east to west motion of celestial objects is caused by the Earth s rotation and is known as diurnal motion .
Diurnal motion causes the position of objects to change throughout the day.
So, whether or not an object is above the horizon depends, in part, on the time of day. But an object above your horizon at a certain time may not be above the horizon at the same time for another observer at a differrent latitude. Hence, an object's visibility depends not only on the time of day but also on the observer's latitude . Some objects rise directly at the east point, while others rise north or south of east. It is important to realize that because all diurnal circles are parallel to the celestial equator objects that rise at the east point must set at the west point.