Here’s why should stop what you’re doing and look up at the sky on August 21, according to astrophysics researcher Jedidah Isler.
On August 21, 2017, millions of people across the contiguous United States will have the opportunity to witness a solar eclipse: the phenomena when the moon’s orbit brings it directly between our planet and the Sun. For roughly 160 seconds, most of the sun’s light will be blocked out and its ethereal, tenuous solar corona will be exposed.
It will be a once-in-a-lifetime event for many of us, but it’s also the most recent crescendo of the epic and ongoing cosmic dance in which we constantly (and mostly unconsciously) play our gravitational role in the solar system. The path of totality for the eclipse — that is, the places in the US where you’ll have the perfect vantage point to see the moon block out all of the sun — is only about 70 miles wide in a diagonal line that goes roughly from Oregon to South Carolina. But even if you’re not along that path, people in the contiguous US can still see the moon covering at least 50 percent of the sun.
Of course, one major reason that I’m excited about the eclipse is because staring at space is my day job. But as it draws closer, I’m getting more and more giddy. It’s like Christmas in August; real talk, it’s Christmas in August plus finding out you actually ARE besties with Beyoncé plus tagging along with Alan Eustace on another stratospheric dive plus the ceiling of the Sistine Chapel, and then some. Here are my five — okay, five-and-a-half — reasons why you should take a few minutes to mark this upcoming moment.
1. The position will be perfect.
Solar eclipses are relatively rare, yet there are still on average two total solar eclipses every three years. The perception of rarity comes from the type, duration and eclipse location as seen from Earth. The most recent total solar eclipse to pass over any part of the US was about 40 years ago. (Fun fact: There are two places in the lower 48 that haven’t seen the path of totality of a solar eclipse in almost 1,000 years. Can you guess which ones? The answer is at the end.)
But there’s an even more interesting aspect to this positioning game — the relative location of the sun and the moon with respect to the Earth is really the secret sauce of a total solar eclipse. The diameter of the sun is about 400 times bigger than the diameter of the moon, and the moon is about 400 times closer to the earth than the sun. Thus, when the three orbits align, the moon is just barely able to block out the sun’s photosphere. Without this celestial positioning, we’d never get to experience the science — or the magic — of a total eclipse.
Astronomically speaking, it’s also a special moment to have such advantageous positioning of our near and dear satellite, the moon, which is slowly moving away from us. That’s right, the moon gets about 1.5 inches further from the Earth every year. In 600 million years the moon will have moved 14,600 miles farther away, and we won’t be able to experience total solar eclipses on this planet because our 400:400 ratio will have vanished. In other words, our positioning in space is truly unique, as is our positioning in time. So count yourself lucky.
Now for you fortunate folks who will be available at the appointed time and place to watch this solar eclipse: PLEASE DO NOT STARE DIRECTLY AT THE SUN. Do not look directly at the sun for any length of time, for any reason. No, not even a glimpse. Technically, you can look at the sun without eye protection at the exact moment(s) of totality, but be VERY, VERY CAREFUL. The sun emits photons that are energetic enough to damage human eyes, so please look skyward only if you’re wearing the proper eye protection (and regular sunglasses do not count).
If you’re not able to witness the eclipse in person, there will be myriad videos and GIFs of this particular event, as well as a hearty archive of previous ones. In 2024, much of the contiguous US will have another opportunity to see an eclipse. For the rest of the world, here is a list of future eclipses throughout the 21st century. And for the sight-impaired, NASA has produced a tactile guide to the eclipse, which is being distributed to schools and libraries for the blind, science centers and museums, state libraries, NASA centers and other institutions.
2. You’ll get a fleeting chance to see the unseen.
While the sun is our nearest stellar neighbor, there is an astonishing amount that we don’t know about it. One of its most intriguing mysteries: that it gets hotter as you travel further from its core. The sun’s photosphere — the part that we think of as “the sun” — is about 10,000 degrees Fahrenheit (5,000 degrees Celsius), but the corona — the otherworldly haze around the sun — is one million degrees hotter than the surface. Weird, right?
The corona is also significantly less dense than the solar surface, so neither it nor the chromosphere (a reddish gaseous layer that is right above the photosphere) can be seen by humans without employing some kind of technology. Scientists use coronagraphs on solar-observing instruments to observe them, but the moon is actually the best blocking mechanism for viewing both of these lesser-known regions of the sun. Solar eclipses also offer a time to better understand the surface of the moon, too. For example, Baily’s beads (shown below) are the beautiful bright edges seen right before the totality that are due to sunlight making its way through the craters and mountains on the moon’s surface.
2 ½. You’ll have a reason to use the word syzygy.
A syzygy (pronounced “SI-zeh-gee” according to Merriam-Webster Dictionary) is the nearly straight-line configuration of three celestial bodies (such as the sun, moon and earth during a solar or lunar eclipse) in a gravitational system. It’s also worth 93 points in Scrabble if you play your tiles right, according to Mental Floss. I’m just saying…
3. An eclipse served as a pivotal moment of science discovery.
One of my favorite reasons to love a total solar eclipse is because it was used almost a century ago by scientists as a giant astronomical testbed for Einstein’s theory of general relativity. The key component of general relativity under scrutiny was whether massive objects can bend space-time itself. In order to tell, you either need highly precise instruments or exceptionally large “test particles” that can amplify small signals. And what could be a better test particle than the sun? That was precisely the experiment conceived by astronomer Sir Frank Watson Dyson in 1917 and later executed by fellow astronomer Sir Arthur Eddington to investigate Einstein’s then-controversial theory. Would the mass of the sun have measurable impact on the path of starlight near the sun-moon-earth line of sight? In particular, would the sun’s mass bend the starlight that passed nearby by the amount that general relativity predicted and more than what was expected from Newtonian physics?
(Spoiler alert: YES!)
In May 1919, the universe confirmed that it could indeed be better described by Einstein’s theories of relativity — and a new era of physics was ushered in. How did the solar eclipse do that? The 1919 eclipse happened to occur near a well-known star cluster called the Hyades. By measuring the cluster’s starlight before the eclipse and during the eclipse itself when the light would normally be swamped by sunlight, Eddington was able to measure the slight shift in position of the cluster based on the gravitational pull the sun had on the light that passed by.
4. A syzygy (used it!) continues to be a time to answer our questions about the universe.
As if confirming general relativity was not enough, there are still experiments being done during solar eclipses to learn more about our celestial neighborhood. The ionosphere — a part of the atmosphere which starts about 35 miles above sea level and extends up to more than 600 miles — helps propagate radio waves and plays a significant part in the aurora, but scientists don’t quite understand how this layer works. Several groups will be turning their instruments towards the eclipse to see if radio transmissions across the ionosphere change during totality and measure the impact of solar radiation on ionospheric transmission. (To find out more about some of the research conducted, go here.)
There are also many citizen-science projects in which the public can participate (there’s even a tool for you to run the general relativity experiment yourself). For example, you can figure out how much the temperature cools during totality, either individually or collectively by contributing to this cool initiative from the GLOBE program. There’s definitely more to be said about citizen-science projects, but I’ll leave that for another day.
5. Eclipse = magic
Despite my giddiness about all the science-related reasons to watch the eclipse, I want to acknowledge a deeply personal one: its power to bring people together. I first became interested in astronomy because stargazing in my backyard made me feel connected to all those who’d come before me and looked up at the night sky. I experienced this deep connection to something much bigger, older and vaster than me, even when I couldn’t yet put words to such awe-drenched emotions. For me, that feeling of connection is heightened by the fact that this eclipse allows for synchronized star-gazing. In about four days, millions of us will be gazing upon the same thing, at the same time, courtesy of Mother Nature. How magical is that?
No matter what reasons move you to watch, I hope you’ll have the time, freedom and ability to see this celestial show we cannot control and should never take for granted. My secret hope is that these moments of connected darkness will spark the beginning of a love affair with space for a new generation of stargazers and from the eclipse’s sweeping shadow will emerge new luminaries in the fields like astrophysics, space science, aeronautics and more.
Answer: The places in the lower 48 that haven’t seen the path of totality of a solar eclipse in almost 1,000 years are Lewellen, Nebraska, and Fort Morgan, Colorado, according to NASA.