Co-authored with Megan Watzke
Today, a growing number of people believe that the Earth is flat and that gravity is a hoax. People are aggressively questioning the legitimacy of climate change and the effectiveness of vaccines. We live in an age where the concept of “fact” is debatable. For people who have spent their careers conducting and, in our case, communicating the value of science, this is a frightening notion.
But it also feels like a rallying cry, challenging us to not give up defending science and attempting to connect with everyone who will listen about its discoveries, impacts, and importance. Enter this week’s recent total solar eclipse, which arrived in North America to the wonder of millions on August 21. This was a rare moment to convince new audiences of not only the beauty of the natural world, but to help explain the scientific method that underpins this incredible natural phenomenon.
Many of our ancestors saw total solar eclipses as harbingers of doom or destruction. The word “eclipse” comes from the ancient Greek “ekleipsis,” meaning “abandonment.” Homer referred to a total solar eclipse in the Odyssey, writing that “the sun has perished out of heaven, and an evil mist has overspread the world." The Sun-worshiping Egyptians never recorded eclipses, leading to a theory that they considered eclipses as too evil to even document. Earlier Hindus wrote about a mythological demon that flew through the sky to swallow up the Sun, while Chinese mythology includes stories of a dragon that would devour the Sun.
It was useful, if not comforting, to create mythological explanations for why the Sun would disappear, why the birds would stop chirping, why the nocturnal animals would awaken in the middle of the day, and why the winds would suddenly pick up and then, just as suddenly, die.
The science of eclipses, however, can be explained by a relatively basic scientific concept: the shadow.
Our Moon is constantly in orbit around Earth, making one complete rotation every 27 to 29 days (this cycle gives us the different phases of the Moon over the course of a month). Meanwhile, our planet is spinning on its axis once every 24 hours.
As the Moon travels around the rotating Earth, it does so very close to the line of sight of the Sun from the perspective of our planet. Almost, but not quite. The Moon’s orbit is slightly tilted, which means the shadow it casts usually does not fall upon the Earth. Once in a great while, however, celestial mechanics will dictate the Moon’s shadow will travel along a particular swath across our planet’s surface. This is what is known as a solar eclipse.
Shadows are everyday experiences that occur when one object blocks or obscures the light from another. Scientists use the common and ubiquitous fact about light to achieve extraordinary results. For example, a medical X-ray involves bone casting a shadow of X-ray light onto film. This X-ray shadow reveals what’s going on inside your body. This is undoubtedly one scientific achievement that most in Western society has benefited from, even perhaps unwittingly.
In space, scientists can use light being blocked by a cosmic object to learn about distant objects. Astronomers have learned about planets trillions and trillions of miles outside our Solar System by watching for subtle shadows cast when a distant planet passes in front of its star. So while this recent total solar eclipse offered scientists a chance to perform experiments and observe the Sun, our nearest star, in an extraordinary way, there was a bigger opportunity. Millions of us were able to stop for a moment to gather some perspective on cosmic objects and contemplate our place in the Universe.
How did the eclipse happen? The Sun and Moon appear to be the same size on the sky and overlap during a solar eclipse, but we know their actual sizes are very different. The Moon has a diameter of about 2,160 miles (3,470 km), a little more than the distance between New York City and Salt Lake. The Sun is much larger in size, spanning some 865,000 miles (1.4 million kilometers) across its center.
Nature, however, has supplied us with a happy coincidence. The Moon is 400 times smaller than the Sun, which is simultaneously 400 times farther way. This allows the Moon to perfectly cover the disk of the Sun during the special occasions of total solar eclipses.
Perhaps these explanations will do nothing to sway those who are determined to believe that scientists are pulling off some grand deception, whether in climate science, in moon landings, or elsewhere. For others, however, a total solar eclipse is an important event that can inspire, amaze, and inform.
Now that the Great American eclipse of 2017 has come and gone, we should remind ourselves that we are surrounded by examples of how science and technology affect and improve our lives every day. For those of us who believe in the importance of science in society, we are beholden to champion science and its impact and help communicate that with others – now more than ever.
Megan Watzke and Kimberly Arcand are the authors of “Light: The Visible Spectrum and Beyond” published by Black Dog & Leventhal. Their latest book, “Magnitude: The Scale of the Universe” by the same publisher will be available on November 7, 2017.