The name “astral” body is mainly used in western esotericism. The name comes from the fact, that this so called body is actually a kind of space traveller, and every night it returns to it’s home, the astral plane of existence, or should I say, sphere.
The astral sphere denotes the lowest spiritual realm, and to be more precise, this is the space the astral body goes to during the night. But because looking from earth, this sphere appears as up, and with the starry sky as a background, the name astral is correct, especially for the sensorial westerners. (astra = stars, in latin) The other realms are said to be the lower and upper devachan. I am sure, that the oriental teachings have the corresponding rupas.
In the sheat, or kosha structure, the astral body would correspond to manomaya kosha.
All apparent divergences come form the fixed nature of any earthy teaching. These teachings are like pictures of a great tree. They only ever show a single point of view. Add the fact that the tree is growing, as everything in the universe - yes even gods develop - and your best bet is to find a genuine school of thought, directed or ruled from the position of actual seership, and one of high level. Many people today have gained various insights into the lower levels of existence, to make things even more complicated. Add the fact that every wrong notion, concept and mental image stands there as a being in the spiritual world, and you might imagine the hardships a genuine seeker of truth must face. In this, the mumbo-jumbo part of yoga or even the moral teachings of religions will help you tremendously, while asana will have very little effect.