In ancient times, people would gaze up at night and wonder about a sky that seemed so vast and mysterious. The narratives of storytellers helped make the unknowable seem familiar and explain how things came to be as they are. That certain points of light moved relative to the fixed background of stars was noticed by some. In Greece, the word planetes, meaning wanderer, was used to distinguish these celestial bodies from the rest of the night sky. This ancient Greek word is the basis for our modern word planet.

Today the night sky can still seem vast and mysterious, but a look back at the quest to learn more about our place in the cosmos reinforces the fact that our home planet is, indeed, a special place. Some cultures around the world evolved with this concept as a point central to their spiritual practice, while others have struggled to appreciate natural resource conservation.

In 1962, Wisconsin Gov. Gaylord Nelson won a seat in the U.S. Senate. A champion of the environment since childhood, he convinced President John F. Kennedy to embark on a nationwide conservation tour in 1963. The president's journey on behalf of the environment was a media flop. Concerned that the effort received such scant attention, Nelson sought other channels to bring the issue to light. He introduced legislation to support clean air, water and limit or ban the use of harmful chemicals such as phosphates and DDT. Nelson found a strong ally in Stewart Udall, the secretary of the interior.

But legislation at the highest levels of government has a limited impact without full buy-in from the American people. Taking a cue from the sit-ins and antiwar protests of the day, Nelson realized that a grass-roots campaign was the path to follow. He issued the call for a nationwide environmental teach-in. He encouraged the nation's governors and mayors of the largest cities to make Earth Day proclamations. In a bid to reach students at all levels of education, he wrote an Earth Day article for circulation in campus newspapers and Scholastic Magazine. The result was tremendous. At the first Earth Day on April 22, 1970, nearly 20 million people participated.

Just before the first Earth Day, two headline grabbing events complemented Nelson's efforts and helped build a sense of urgency for environmental causes. In 1969, the Cuyahoga River caught fire when oil and other pollutants ignited. And NASA released the iconic image of Earthrise above the lunar horizon. Speaking about the photo, Apollo 8 astronaut William Anders said, "We came all this way to explore the moon, and the most important thing is that we discovered the Earth." Another famous NASA image, The Big Blue Marble, was adopted for design of the Earth Day flag.

Years later, at the urging of Carl Sagan, NASA controllers turned the camera aboard the Voyager 1 spacecraft toward Earth and took a picture. At the time, Voyager was nearly 4 billion miles from home. From its distant vantage point, Voyager's image showed Earth as a tiny speck of light, less than a single pixel in the camera array.

Sagan addressed the significance of the image in his 1994 book, The Pale Blue Dot. If you are not familiar with it, take a moment and look up the passage known as Reflections On A Mote Of Dust. A search on the Internet will quickly find it.

Make time to celebrate Earth Day this week and remember that even though the official date happens just once each year, stewardship of our natural resources deserves daily practice.

Peter Lipscomb operates Astronomy Adventures guided night sky tours and advocates for sensible and energy-efficient lighting practices through public outreach and education. Contact him at peter@astronomyadventures.com.