In the Marvel Universe the Astral Plane is a metaphorical level of existence with ties to the physical world which only psychic entities can visit. Doctor Strange has practiced astral projection since his inception in 1963. Other Marvel characters with no psychic powers are capable of astral projection through other sources, such as by magic spells - for example, Magik was able to astral project her own consciousness in New Mutants (Series 1) #15. Other mutants such as Professor X, Emma Frost, Jean Grey and other powerful psychics have access to the astral plane. As a means to prevent another powerful psychic from harming others, Professor X imprisons the Shadow King on the astral plane. There are beings who live in the astral plane of existence such as the Mummudrai, of which Cassandra Nova is a member, who cannot exist on the physical plane without a body. Some say it is an alternate universe in an equivalent space to our own, where all matter is composed of ectoplasm. On the astral plane, the life energies and consciousnesses of other beings are discernible to adepts. Adepts can reach the astral plane by psionic or magical means. The astral plane is also sometimes called astral dimension, astral realm, or spirit world.