Shirk

The are a number of narrations indicating that the Imams (A) had comprehensive knowledge of astrology, and you can find them in books such as volume 55 of Bihar al-Anwar. (Whether one accepts them is a personal decision, but there are no narrations to the contrary.) One narration (the "Myrobalan Fruit") implies that astrology exists as a way to prove the existence of God and the prophets' knowledge from God. 

Whether or not astrology is considered shirk has tended to depend on worldview. If someone is an atheist and believes that there is no God but that the stars and planets control their destiny, then this is shirk. If someone believes that their fate is wholly fixed by astrology, and that God cannot change it, this is also theologically inappropriate.

If someone believes that God is in command of the entire universe, and astrology is part of the divine plan, and that our ultimate fate is in the hands of God, this is not shirk.

Some Muslims today are too eager to throw around the word "shirk" without thinking about what they are actually saying.  

Insofar as Allah has granted us an imaginative faculty and the creative faculty, it is not shirk to imagine a future that we would like, or to change our thinking (as long as it is not causing harm or something haraam).

Of course, you will still need to study for your exams! 

In the modern era, some Muslims have become very sensitive to the question of shirk by considering any number of physical objects to be shirk. This includes sacred objects, shrines, etc.

(This idea primarily comes from Wahhabism and Salafism, but some other Muslims have taken it on board too.)

Similarly, Wahhabism and Salafism reject most forms of intercession as shirk, whereas many Muslims before that accepted the idea of intercession.

The Qur'an itself does not state that the notion of sacred objects is shirk. Rather, shirk is when you directly worship beings other than Allah.

So, keeping an alam, in and of itself, is not shirk.

Possibly, some views are cultural. Since alams are most common historically in Iran and the Indian Subcontinent, it has been more common for Shia in other regions, where alams were not common, to criticize the practice. (That is, it was seen as being culturally different and hence suspicious - man is an enemy of what he does not know.)

On the flip side, some Muslims in the Subcontinent have felt cautious about the cultural influence of Hinduism, and so for this reason try to avoid physical objects in devotional practices. (We tend to be most cautious about the things we are closest to, which might be seen as a competitor.) Although I think this is less common.