This circle divides the sky into an eastern and a western half. When an object is rising it is to the east of the meridian, and when it is setting, it is to the west of the meridian. The part of the meridian above the horizon is called the upper meridian and that below the horizon is known as the lower meridian . When an object crosses the upper meridian and is at its greatest angular distance above the horizon, it is said to be at upper transit . At lower transit an object usually lies below the horizon on the lower meridian.
Objects are at upper and lower transit once each day.
The NCP lies directly above the north point on the horizon. Polaris is the last star in the handle of Ursa Minor, better known as the Little Dipper. Figure 2.2 is drawn with the Earth at the center of the celestial sphere. An observer is shown on the Earth in the northern hemisphere at middle latitude. As always, the point over the observer s head is the zenith and the point underfoot is the nadir.