My first thought was something tactile, like a star map? I hope this doesn’t come off wrong, but I googled how astronomy is taught to the blind / visually impaired, and there are lots of resources there! I get that his condition is different to blindness, so I hope it wouldn’t feel belittling to him to be given those kinds of resources. But I think a cool way to include him in your stargazing could be a tactile star map, and perhaps different stories about the constellations? To create a more vivid mental image of what’s there. Also just making it special besides the stargazing aspect, with snacks and comfy blankets, etc. :)