The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. ... The Universe contains billions of galaxies, each containing millions or even trillio...
The trillions of stars in space differ in size, mass, temperature, and brightness. The brightness of some stars, called variable stars, varies with time. Some form families of two or more stars or orbiting each other - these are called multiple stars.