When people are asked to choose a number between one and 10, the most popular choice is 7, all over the world. 7 is a number that appears in nearly every facet of human life. Here are just a few examples: 7 is the number of periods (or rows) of elements on the periodic table in chemistry. On a more aesthetic level of science, ROYGBIV (red, orange, yellow, green, blue, indigo and violet) are the 7 colors that make up white light—these are also what we marvel at in each rainbow. With very few exceptions, all mammals’ necks have 7 bones. In addition to the traditional 7 seas in many cultures, 7 is also the number of stellar objects in the solar system visible to the naked eye: the sun, the moon, Mars, Mercury, Jupiter, Venus and Saturn. There are also 7 external holes in the human head: two eyes, two nostrils, two ears and one mouth.
