How did astrology come into existence? Why do people believe in it so much?

How did it come into existence?
Astrology is science of probability and statistics.
Our ancestors were intelligent people. They could predict movement of planets, eclipses, transitions, retrogrades quite precisely. Every branch of science rely heavily on observations. The early astronomers did observations and figured out the math and patterns behind the movement of celestial bodies.

If you look closely, the Indian astrology is also science of psychology. Over the years of research the ancient sages found patterns in human behavior. If we do that now, the obvious question would appear in our mind that what could govern behavior of a person? Does the time when s/he is born have any relation with the way s/he will behave? Is it set of chemicals? Is it geographical conditions?

Now if one wants to predict it, one needs to correlate the patterns with something. After correlating, there comes observation part, observing if at all there is correlation between those two seemingly separate events. (err Butterfly effect? ) After finding reasonable relation between the patterns over years and generations of observation one can safely form a complete branch of studies over it.

What weapons were used in an early 1980's US Army fire team?

This question may be using "fire team" in the strict definition. A "fire team" is half of an infantry squad, which would be armed with M16's and M-203's (an M-16 with a 40mm grenade launcher mounted coaxially under the barrel. In addition to the primary weapons, individual

Which U.S. city has the most interesting architectural monuments?

There has long been a common consensus -especially among architects - that it is Chicago. The modern skyscraper was developed in Chicago (and not in New York) at the turn of last century. Some of the best works of the greatest architects in recent times, like Frank Lloyd Wright and Mies Van der Rohe, 

Which basic human invention is also likely to be found on an alien planet, assuming aliens exist?

That would be difficult to say. We have to assume that these aliens have reached a certain level of development which would mimic ours, which is unlikely. Aliens could be totally different than we can imagine, but assuming some parallel development, maybe the wheel?