Where is heaven? If there are bodies in heaven, then surely they must be somewhere in space? Is that the case?
The short answer to your question is no, that is not the case. Let’s see if we can explain and understand this, as it is a bit tricky.
As you imply, if there are bodies anywhere in the universe, their position in space can be known and described with reference to all other bodies. They might be light-years away from each other, but we can define their position and know in which direction we must travel, and for how long, to get to them.
This is the case for all material bodies. So, if in heaven bodies are like that, we should be able to know where they are in the universe and travel to them, perhaps in a spaceship. Can you imagine going to heaven in a spaceship? Obviously, we can’t do that.
The reason is that the bodies in heaven are not material, as are earthly bodies. They were once material while on earth, but now they are spiritual. We see this, for example, in the case of Jesus’ body after the resurrection.
While his risen body bore the wounds of the crucifixion and he could eat food, he could also suddenly appear and disappear, as he did with the disciples of Emmaus (cf. Lk 24:13-31), and he could pass through closed doors, as he did when he appeared to the apostles in the Upper Room in the evening on Easter Sunday (cf. Jn 20:19-20).
So too, Our Lady, when she appears on earth as she has done numerous times throughout history, suddenly appears and then disappears. She is seen with the eyes and she can speak in the language of the person to whom she appears, but if that person approached her and tried to touch her, he or she would not feel a material body. Her body, like that of Christ, is spiritual, not material.
This is the case with all bodies in heaven. Perhaps the prophet Elijah, who ascended into heaven in a chariot in a whirlwind (cf. 2 Kings 2:11) and St Joseph, the husband of Mary, are also there in their bodies. The myriad of angels too are in heaven adoring God, but they, of course, are pure spirits. They never had a body.
But that still leaves the question of where heaven is. It must be somewhere. But when we say that, we are still thinking in terms of material bodies, which exist in space with a definite, definable, location. But heaven itself and everything in heaven, including God himself, is spiritual. It is not in space, as we know it.
A good way to understand this is to ask where God is. If heaven is the state in which we see God face to face, then heaven is where God is. But where is God? Again, when we ask that, we are inclined to be thinking in terms of space as we know it on earth, the space where material bodies are, where the universe is. But God is not in that type of space. He is pure spirit, and he is in a different realm altogether, the spiritual realm.
In this sense, we cannot say that God is in some particular place, or that he is in all places, as pantheism does. He is outside the space of material bodies, in a realm of his own. We say that God is everywhere, not in a spatial sense but in a spiritual sense.
He is everywhere by his providence, guiding all beings to their end. He is everywhere by his knowledge, knowing everything and everyone, no matter where they are. He is present everywhere by his power, holding everything in being, just as he created everything out of nothing.
So God, and heaven, are in the spiritual realm, not in the physical realm of our universe. But that does not mean they are not real. God is not only real, he is reality. He is being itself, he is who is, as his name Yahweh means (cf. Ex 3:14). Everything comes from him, receives its being from him. So too, heaven is real.
Apart from the numerous Scriptural passages which speak of heaven, there are thousands of people of all religions and of none who have had near-death experiences, in which their soul left the body and experienced the indescribable happiness and love of God in heaven.
One day, we too hope to experience it. Then we will see how real it is, wherever it is.