The Astral Body
Humans have been aware of the idea of an astral body double of themselves for millennia. The spirit body is a large part of many ancient cultures, such as those of Mexico, Egypt and Tibet. In these ancient cultures it was believed that one could leave one's earthly body behind and travel far, very far, on astral adventures.
The Egyptians called the astral body the KA, their name for one's spiritual body that took the shape of a bird and left the body upon death. It is thought that the Egyptians imagined their version of the astral body to be birdlike because it could fly, soaring across the landscape and ascend high into the clouds.
Many Tibetans have long believed in what they call a 'radiant body', which is much closer to how we think of the Astral Body inn the West - i.e. an almost exact glowing/ghostly replica of ourselves. The Tibetan Book of the Dead, Bardo Thodol, describes the process of dying and how one's consciousness leaves the body in its astral form and travels onto the next life.
For most of us the astral body is invisible, and in fact we only see or become aware of our own astral body or its silver cord when we astral project are have an out of body experience. It is thought that some people can see astral bodies all the time, or at certain times - like when someone dies.
You astral body may not always be a replica of yourself. It may be simply a glowing presence, a ball of light or a faint ethereal shape. I always think of it is being me, looking like me, and have had various lucid dreams where I see myself looking back at myself from both sides, which are pretty much the same. However lucid dreaming is not quite the same thing as astral projection or an out of body experience, though it can lead to either or both of those events. Still, it is widely believed that when we leave our body in an astral form, it is our consciousness that is leaving and the body is all but an empty shell. However, unless we have died, we still have a tangible connection to our body, often perceived as a silver cord. The silver cord is like a sort of tether to our earthly body, a way to find our way back and a connection that keeps our sleeping body functioning. You may sometimes feel it pulling you back.
When you first experience your astral body and travelling outside your body it can be a little frightening, it certainly was for me. At the time I'd been reading a book called Practical Time Travel, which utilizes astral projection to flip through the Akashic Records and venture into different points in time. I followed some instructions in the book, laying on my back on the floor, and imagined myself leaving my body. The really frightening part was that it worked! I found that I was floating a couple of feet above the floor. It only last for a few seconds as I panicked and was snapped back inside my body again. My hands were shaking from excitement and adrenalin.
It was actually quite a while before I gave it another try, and much later that I became really comfortable with it. I sometimes suffer from sleep paralysis, which is another scary phenomena, but I found that if I just go with it and try not to struggle it with often transform itself into an out of body experience and thus into astral projection - if I can stay relaxed and let my higher will and desire to move around in the astral plane and not think about my body back in the bed, or other thoughts of earthly life creep in.