There often is confusion regarding the Astral Projection rules.
While projecting a person is able to view the astral form of the world. This is a colorful place in which technology has almost no footprint. Things which are alive are a rainbow of colors while things which are not are simply black or gray.
It is important to note that things which were created to be transparent, like windows or glass, will still be transparent on the astral plane. You can see through them, but it will hinder your vision
The Earth itself is alive, preventing movement into the ground. If you try and travel outside the atmosphere you will find madness or death.
If you wish to interact with the physical world, you can manifest. When you do that a ghostly form of you appears and is able to be seen and heard by the physical world.
You cannot cast spells at targets which are not also present in the astral plane, seeing someone's aura is not enough to target them. On the flip side, unless someone is dual natured, or has manabased spells, they cannot affect your astral form (though they could go after your meat).