Lectures everyday. A lot of information. However, regarding asanas (poses), only one per day.
I don't know the concept of "astral world".
From my teachers, the ultimate goal of yoga practise is the enlightenment. Physical practise is the path towards that.
However, very very few people reached the goal. It doesn't matter. The process itself is beneficial enough. I love it.
There are many forms of traditinal yoga. Yoga does have 8 different aspects. However, very few people are aware of them, for sure.
Traditionally yoga was not a popular thing. Only a few people did it. The teaching was never like what you see now. There was no school, no class. It went through a master-deciple way, somehow like how martial arts was taught in China hundreds of years ago. A young kid would be sent by his family to serve a yogi as a deciple. The yogi enjoyed the service of the deciple, and when he felt right, he would teach a bit. If the deciple is smart enough and lucky enough, after some ten years or longer he may accumulate a lot from the teaching. Eventually he will become a new yogi who carried down the thing, then he repeated the process he had went through: accepting his own deciple, and on and on.
Modern yoga has a pretty short history of less than 100 years. While the philosophy can be found in books, most yoga practitioners don't really know it or follow it. That's understandable, because the asanas are the start. Over time when people are good at asanas, naturally they would proceed and dig deep into to the philosophy part.
Simply with the basic knowledge and asanas, I myself already found it good for me. The physical benefits are regarded as the side effects of yoga. To many people, such side effects are their purpose. That's fine too.