1. Activity: A Human Nebula
A nebula may look like a cloud or colorful smoke, but while a nebula may have as many as a thousand (103) particles per cubic centimeter, the air you are breathing right now has something like 1019 particles! In other words, even the thickest looking nebula is as empty as the best vacuum we can make on Earth.

2. Activity Questions
Suppose your body has 1023 particles per cubic centimeter.
A) How many times more particles per cubic centimeter do you have compared to a nebula?
B) How many times bigger would you have to be if you were a nebula?
C) How big would you be as a nebula?