It’s desirable to treat these two subjects together because of the confusion in terminology over the years. Astral projection is a particular state of consciousness in which the astral body separates from the physical and is able to travel on the astral plane, obtain information, communicate with other beings, and return to the physical with full memory. It is commonly said that the astral body separates from the physical during sleep, but does not travel. Non-physical movement in the familiar physical world is more likely to involve the Etheric body than the astral. The etheric is the energy double of the physical body, able to function separately from the physical body while connected to it with the ‘silver cord’ that transfers energy and consciousness between the two.
The etheric body can travel anywhere in the physical world, moving with the speed of thought, and can interact with the physical in a limited manner.
The Astral Body does not leave the physical body because it is not really an independent body but is the sub-conscious mind and "moves" within the field of consciousness without moving at all. Consciousness is everywhere, and in consciousness you can be anywhere. To the extent you want a body, you need to create a Body of Light in your imagination and then just imagine it doing what you want, going where you want.
But, the astral plane is not the physical world, and it lacks the "solidity" of the physical plane even though there is replication. However, things may appear on the astral that are not in the physical.