Describing your visit to a planetarium should include all the details about your visit. It should have information like planetarium show timings, with whom you went, and things in the Planetarium.
In the simplest words, a planetarium is a place that gives the education of the planets and galaxy. The ceiling of the planetarium is a dome where the images of stars, planets etc are shown. A projector might also be used to show the images.
In the introduction, write the name of the Planetarium and where it is located.
In the body part, write the reason why you visited the place. Also, mention with whom you go there. Describe everything presented at the planetarium show. Write about all the planets that were described during the show.
In the last paragraph, write about your views and thoughts about the Planetarium show and all that you liked about the place.