Astral Planes can only be opened with "[CONT](VC):If your (VC) has five or more force markers, your back row center (RC) becomes an Astral Plane.".
As long as the specified conditions are met, your rear-guard circle becomes regarded as an "Astral Plane". The affected circle is still considered to be a rear-guard circle.
While an Astral Plane exists on your field, you will able to call an Astral Deity to that zone. Astral Deities cannot be placed elsewhere, nor even be ridden. Only an Astral Deity can exist on that zone; should any other units or locked cards be put, the card is immediately sent to the drop zone.
However, a unit's "When placed" ability will still activate. Resolve said ability, then proceed to move the rear-guard into the drop zone.
At the end of your turn, if there is still an Astral Deity on an Astral Plane, you must put it on the bottom of your deck.
An Astral Deity can be normal called regardless of your vanguard's grade.
An Astral Deity can attack even from the back row and perform drive checks, as well as activate its abilities. Any cards revealed for that unit's drive check must be put into the soul instead of going to the hand.
When an Astral Plane is open, if there was a non-Astral Deity rear-guard or locked card originally on it, that unit or card must be put into the drop zone.
When an Astral Plane is open, it retains all gift markers that are already on it. Likewise, you may further put gift markers on it.
An Astral Plane will close when your Opener is no longer your vanguard, or loses its ability to open the Astral Plane (such as by being deleted or Stridden over).