Comets are small compared to planets, the largest being about 100 miles in diameter. They are made of frozen gasses such as carbon dioxide, water, nitrogen, and methane, as well as dark carbonaceous or rocky matter. Comets can be thought of as huge dirty snow balls. Their orbits sometimes bring them close enough to the Sun to be visible. They then warm up, sublimate, and cast out a plume of matter that is pushed out by the pressure of solar radiation. This is the comet's tail.
The nearest star to us is our Sun. Other than our Sun, the next nearest star is Proxima Centauri 4.3 light years away. A light year is the distance light travels in one year going at 186,000 miles per second, or 98,000,000,000 miles. On scale with this model Proxima Centauri would be 34.4 miles away, down at the Jersey Shore in relation to the location of the Planet Walk.
The Sun, Proxima Centauri, and over 100 billion other stars comprise the cluster of stars that we call our Milky Way Galaxy. The next nearest galaxies are the small Clouds of Magellan and the dwarf galaxy Sagittarius. Our Milky Way Galaxy is only one hundreds of millions of galaxies in the vast expanse of space and time that we call the Universe.