This question confuses an arboretum with a planetarium. There are many nice places to see plants, but only one public planetarium in Omaha. The Planetarium sky is projected from a special instrument designed for doing just that. Therefore, it is available at almost any time. The Universe contains an infinite variety of topics.
Astronomy is a very diverse field.
That would be impossible. In the first planetaria, simple lectures about the night sky sufficed. The wonder of seeing the stars indoors amazed people in the 1920's and 1930's. At that time there was no projection video, no computers, no telescopes in space. Today we havemany exciting stories to tell, from the tremendous discoveries of space probes to current sky events.