Today we begin our journey to attempt to understand the Universe in which we live. But before we talk about what modern astronomers know, it is important to look back to see where astronomy came from, because much of the language and structure of astronomy owes itself to ancient ideas, beliefs, and traditions. Before we do so, however, you must purge your mind of what you know, or think you know about the Universe. Pretend we are prehistoric cave people. Back some 20,000 years or so, humans were not arranged in complex societies (about the time the last ice age ended). They basically were "hunter-gatherers". A nomadic lifestyle. We do not know much about their belief systems because they left few traces of their existence, as they rarely stayed in one place long enough to leave a significant record of their presence (though they did leave some traces, such as the cave paintings at Lascaux, dating from 17,000 years ago). Some term them "intelligent animals".

For these people, the Universe was a mysterious place, for they could not comprehend the real reasons why most natural events happened. For example, how do you think they felt during a thunderstorm? Did they do something to bring on such a storm? Even though they did not understand much about the Universe, they certainly soon became aware of certain astronomical events and cycles. Obviously, they knew about night and day. The Sun, whatever it was, would always rise in the East (even though they may not have had a word for East!), travel across the sky, and set in the West. They understood that there then would be a period of darkness before the Sun would again rise.

They certainly also became aware of the Moon and the stars. The Moon would slowly move amongst the stars while constantly changing its appearance. They would probably be able to predict the time of full Moon, as at these times it would be bright enough at night to allow them to hunt (or to be hunted!).

These people might have been aware of the yearly seasonal cycle. There would be times of cold weather, and times of warm weather. Various types of food, such as fruits and vegetables, would be abundant during the warm times of the year. During some times of the year, different types of game animals would be migrating, and they would probably follow them. While we do not have any clear evidence for this type of knowledge among the prehistoric peoples, we know from studying existing tribes of people on this globe that such traditions are still alive and well, and probably remain relatively unchanged in the intervening eons.

For reasons that are not yet completely clear, some 15,000 years ago, agriculture appeared on the scene. Various types of animals were domesticated, and humans began to purposely grow food, instead of merely "collecting" it. Before the development of agriculture, the Universe was more difficult to understand because you would have had to always be "on the move", and it was difficult to recognize the repeated cycles and patterns of celestial motions. There was not much time for reflection. With the rise of agriculture, and we include ranching and fishing in this term, food was not so hard to come by. With experience, you could grow sufficient quantities of grain to get you through the winter. Or you could dry fish and other meats, or use your live animals for food during the winter. Some years you might end up with more of a particular type of food than you needed to survive the winter---you could trade this with a neighbor to get some different type of food. Thus, people were now able to stay in one place, and now could pay more attention to natural cycles. These cycles were especially important for agriculture--you had to know when to plant your seeds, or when to move your sheep to better grazing lands.

The development of agriculture leads to the origin of astronomy. For example, you would quickly notice harbingers of the coming spring by watching the motion of the Sun and stars. Fisherman would notice how the movements of the Moon would affect the tides. With sufficient observation you would notice that there was a predictable pattern: a certain number of days would have to elapse between when the Sun would again rise at a particular spot on your horizon. You would develop a system that would allow you to predict when it was time to plant your grain. You would devise a calendar. The beginning of each new cycle may have been cause for a celebration---the first "New Year's" celebrations.

Of course, it became quite clear that just because it was officially "spring", it did not mean it was warm enough to plant your grain. The weather was only partially tied to the motion of the Sun in the sky--some years were good, some years were bad. A bad year might lead you to suspect that you had done something to upset nature, you may have angered the Sun for example. It is not too hard to envision the early rise of religion to attempt to understand these events, and with that, various ceremonies designed to placate these celestial beings. With these developments, we get a new type of profession: the priest. A person who's sole job it was to understand and read the signs of nature, and of course, to keep track of time so that all of the necessary ceremonies occurred on schedule to keep the gods happy. Of course, it was also the priest's job to suggest remedies when things went unexpectantly wrong.

With the rise of priests came more careful observation of natural cycles. The earliest records of "calendars" appear to be various alignments of stones, and of pre-historic buildings. Most of these are of the "horizon-intercept" kind, they were aligned with where the Sun (or Moon) rose (or set) along the local horizon. One example you are almost certainly familiar with is  Stonehenge.  Activity at the site of  Stonehenge appears to date back to 7,000 BC, but the construction of the main parts of the monument appear to have begun around 3,000 BC. The various structures we see today at Stonehenge appear to be carefully aligned with the horizon locations ("azimuths") of the risings and settings of the Sun and Moon at various extremes in their motion (furthest south, furthest north, etc.). During this time, similar structures were being constructed elsewhere in the world, in both the Middle East (Babylon and Egypt), and in the far east (India and China). Later, such structures arose with the Mayan/Aztec culture in the Americas (reaching their peak circa 200 AD, though archeological evidence suggests their culture began about 1500 years before it reached its peak).

The first actual "calendars", as we would recognize them, appeared on the scene about 6,000 years ago (here is an excellent site on ancient calendars). The Chinese calendar appears to have begun in 2637 BC (go here  for more on Chinese calendars), while the Egyptian calendar (from which our modern calendar arose) appears to date from 4236 BC! These calendars even had systems to account for the fact that the year is not exactly 365 days long (why we have "leap" years).

As observations became more careful and accurate, cycles were noticed, as well as other phenomena: the discovery of the planets, and their motions. The appearance of comets, and "new stars" were noted. Of course, to keep track of all of this, writing had to be developed, as well as mathematics! With these developments, ancient cultures were able to predict astronomical motions and events well into the future---the most extreme case probably occurred in Mayan culture, with some events recurring on cycles that had periods of 3 million years!

Thus, its pretty clear that the origin of astronomy (and science in general) can be traced back to the rise of agriculture.