The rings of Saturn or the blue and green beauty of Earth inspire creative Halloween costume ideas. If you want to dress up as a planet, there are several approaches available. Choosing a planet with a distinctive visual cue, like Jupiter with its great red spot, will help your costume make sense without explanation.
The main considerations for a planet costume are shape and outer appearance. One way to create a large roundish costume is to stuff an oversized shirt and sweatpants with pillows or blankets. For children, a large spherical paper lantern with arm holes cut out can form the base of the costume. Spray paint the surface of the costume with the colors of your chosen planet. Cut out continents from a large world map to form stencils to paint planet Earth.
Saturn, Jupiter, Uranus and Neptune all have planetary rings of varying prominence, though only Saturn's are so iconic that a costume would be incomplete without them. One way to create rings is to cut a large circle of cardboard with a hole in the middle and attach it to the middle of your costume. Paint rings of brown, tan and white onto the cardboard or cover it in foil or sparkles. An arguably simpler option is to carry a hula hoop with you and give it a spin every so often.
The best approach for adding moons to your costume depends on the number and size of the moons. Mercury and Venus have no known natural satellites, while Jupiter has over 60. For an Earth costume, you can simply paint a ball gray or cratered and carry it as the moon. Create lots of small moons by attaching foam balls to wires or sticking them directly to your costume. Pluto's moon, Charon, is relatively large in proportion to Pluto, so you can make a couples' costume by dressing in icy grays together.
Another approach is to dress up as the sun or the solar system, with planets in orbit around you. You can create a solar system hat by attaching small polystyrene spheres to a round yellow hat using different lengths of heavy-gauge wire. For a larger-scale costume, cut a large circle of cardboard with a hole in the middle that will rest on your hips and draw orbits onto the circle. Attach balls to the orbits with wire or glue and wear bright yellow sweats.