When light travels through outer space, it bends and refracts. Demonstrate this to your students by performing a simple experiment that visually bends an object, as suggested by RWA Scientia. Fill a clear glass or jar halfway up with water. Insert a pencil or a pen into the container. Hold a second pencil or pen outside the container parallel to the one inside. The students will be able to see that the pencil outside of the container appears straight, while the pencil inside the container appears to bend.
The planetary and stellar bodies in the universe are held by gravitational forces. Demonstrate gravity to your students by re-enacting Galileo's Free Fall experiment, as described at Reeko's Mad Scientist Lab. Have your students sit on the floor three to four feet from you. Place sheets of white paper on the floor to make the demonstration easier to see. Hold a small marble in one hand, and a baseball in the other. Keep the two objects at the same distance from the floor. Drop the two objects at exactly the same time. Although they weight different amounts, they will hit the floor at the same time.
The colors seen on other planets, galaxies and nebulae are indicative of which elements and gases are present. Each color in the spectrum is split from white light and represents a specific gas or element. Demonstrate this to your students by splitting sunlight into a spectrum of colors in an experiment suggested by Csiro. Fill a clear glass halfway up with water. Set the glass on a table that has a direct ray of sunlight hitting it. Place a sheet of paper on the floor so that you can see the resulting rainbow spectrum of colors.