Solar System in Perspective

Consider our solar system. It includes the sun, the nine planets, and a host of other curious objects. It is far larger than most people appreciate. Just for the sake of curiosity, I wondered what it would be like to create a scale model of the solar system; one that would fit, say, in my backyard. How large would the sun and planets be on a backyard scale like that? To make the model solar system fit comfortably in a backyard, my model sun had to have a diameter of 0.1 inches...about pinhead size. Here are the specifics:

Object	Diameter in km	Distance from Sun in AU	Model Diameter in Inches	Model Distance from Sun
Sun	1,392,000	n/a	0.1000	n/a
Mercury	4,878	0.31	0.0004	3 inches
Venus	12,104	0.72	0.0009	8 inches
Earth	12,756	1.00	0.0009	11 inches
Mars	6,795	1.52	0.0005	16 inches
Jupiter	142,985	5.20	0.0103	4 feet, 9 inches
Saturn	120,537	9.55	0.0087	8 feet, 7 inches
Uranus	51,119	19.19	0.0037	17 feet, 3 inches
Neptune	50,538	30.06	0.0036	26 feet, 11 inches
Pluto	2,320	39.34	0.0002	35 feet, 3 inches

If the sun were the size of a pinhead, the planets would be incredibly small. Just to put this in perspective, a typical human hair is approximately 70 microns in diameter. One micron is ¹/_25,000^th of an inch, so that hair is a full 0.0028 inches in diameter. That is huge compared to some of the planets in our model solar system. For example, Mercury orbits 3 inches from our pinhead sized sun, but is only 1/7^th the diameter of a human hair...tinier than a dust mote. Earth orbits a respectable 11 inches away, but is only about 1/3^rd the diameter of a human hair. Even the goliath, Jupiter, orbiting at 4 feet, 9 inches is only the width of 3 human hairs. The tiny little speck, Pluto, orbits 35 feet distant, on the other side of the yard. Take a look at this graphic I made showing the distance between planets to scale.

This pinhead sun and its associated planets are contained in a spherical space about 70 feet in diameter. The heliopause demarks the outer boundary of influence our sun has on surrounding space. Although not yet measured, it is believed to be located at about 120 AU. That's equivalent to 108 feet in our model. So, this pinhead sized sun controls what goes on in a 216 foot diameter sphere of space surrounding it. Pretty amazing for a little pinhead!

From this exercise, I get a new feel for how empty space is. Our solar system condensed out of a massive cloud of interstellar gas and dust about 4.6 billion years ago. Considering how tiny the sun and planets are compared to the vast volume of space in which they reside, I'd say this interstellar cloud was not very dense. A mere wisp in the vast void of space.

For additional perspective, consider that the next nearest stellar system is Proxima Centari at 4.2 light years. In our model, this pinhead sized neighboring star would be 45 miles away. Our Milky Way galaxy is made up of approximately 200 billion stars of which Proxima Centari and our Sun are but two. It is shaped like a huge disk, 90,000 light years in diameter. In our backyard model, our galaxy would be about 1 million miles in diameter. The next nearest galaxy, Andromeda, is 2 million light years away. That would be equivalent to 21.5 million miles in our backyard model. Consider that there are an estimated 10 billion galaxies in the observable universe with a total of 2000 billion billion stars in all. The edge of the observable universe lies approximately 15 billion light years distant. That's equivalent to about 161 billion miles in our model.