The practical importance of astronomy in ancient times is that it allowed people to navigate. The land on the earth changes frequently but the stars do not. The saying,”Follow the North Star” that means if you find your self lost and without a compass this Star will show where the North is located.
Answer: the mosaics in San Vitale differ from the rest of the structures and artworks we have seen because they are all about god being on their side and having imperial might.