We call these apparent motions, because they can be produced by motions of the observer as well as by the objects themselves. Most of these motions are so slow that if you aren't a practicing amateur astronomer, you probably aren't aware of them. The best way to visualize them is in a planetarium or with a good computer sky simulation program. We will use one of these in class, called Starry Night . Half of Earth is always in shadow.
Horizon plane is different at each location on Earth.
The extra amount is 4 minutes, on average. Given the modern boundaries of the constellations, there are 13 of these, as in Table 1-1 of the text. Sun therefore moves north and south of the celestial equator during the year. The change in the shadow distribution on the Earth's surface caused by the tilt is quite dramatic. The shadow moves westward on the surface.