Mary,
the Galaxy sensory bottle seems similar to lava lamps, just without the bubbles to keep them going. I found these instructions: https://capturingparenthood.com/oil-water-galaxy-sensory-bottle/
I’m interested in how you are starting BIG (with galaxies) and coming step closer to home each day, to stars, then the solar system and then near the Earth to the Moon. Ending with aliens is fun, since we don’t have proof that they exist, but the very scale of the galaxy means that there is likely life out there. (Unless you accept the Fermi Paradox).