On Sunday afternoon, three-and-a-half-year-old Zachy and I were out in the backyard searching for bugs. All of a sudden he looked at me and said in his most serious voice, “This is Earth. Earth is our planet.”

I nodded solemnly. …

Mythology and literature have frequently told tales of people who went on a journey and in the process discovered more about themselves. Some of these stories, such as Homer’s Odyssey (written in the 9th century BC) and Chaucer’s Canterbury Tales…