The size of our solar system alone—not to mention the Milky Way galaxy—is so large that it defies imagination. Let's try to visualize it on a scale we can begin to comprehend.
Let's first envision our sun as the size of an orange. On that scale, the earth is a grain of sand orbiting the sun 30 feet away. The gigantic planet Jupiter, many times larger than Earth, is a cherry pit circling 200 feet away. Saturn, the size of a slightly smaller cherry pit, orbits two blocks away from the sun. Pluto is another speck of sand almost half a mile from our orange-sized sun.
How does that compare with distances within our galaxy? On that scale the sun's nearest neighbor, the star Alpha Centauri, is 1,300 miles away. Our galaxy, on that scale, could be compared to a group of 200 billion oranges, each an average of 2,000 miles apart, with the entire group forming a cluster 20 million miles in diameter (more than 4 1 / 2 times the actual distance from the earth to the sun).
Based on research using their most advanced telescopes and other tools, astronomers estimate that 100 billion or more galaxies exist in the universe. They haven't yet found an end or edge to the universe; this is simply all we can detect using our most advanced instruments to peer 10 billion light years into space. Such distances make human space travel beyond our solar system impossible. (Adapted from Robert Jastrow, Red Giants and White Dwarfs, 1990, p. 15).
The amount of matter and energy in the universe is unfathomable to the human mind. We describe distances and space in terms of light-years—the distance light travels in one year (almost six trillion miles)—as though we comprehend it. But we cannot begin to understand these kinds of figures. Still we must face the question: How did all this come to be?