This part sends shivers up and down my spine each time I watch it. I don't know whether this was intended, but it looks to me as Astro is having a Near-Death-Experience with Uran meeting him on the other side. He's trying to reach out for her, but instantly Uran draws back and vanishes.
I think this scene is very reminiscent of our loved ones in the hereafter. Although we can't physically hold them in our arms anymore, they're very much alive and around us all the time. We may not see them with our physical eyes, but we can feel their presence if we want to.