Today, Americans across the country will pick up special glasses and head outside to view a celestial event nearly a century in the waiting. Nicknamed the Great American Eclipse, the rare daylight phenomena marks the first time since 1918 that the moon's shadow will race across the contiguous United States, giving millions of people a rare chance to witness the sun covered by the moon in totality.
Indeed, today marks an end to what many consider the "dark ages" of solar eclipses over American soil. Whereas the 20th century only had two total eclipses, in 1918 and 1970, over large amounts of the U.S., the 21st century will have no fewer than six prime total eclipses, with four of them occurring within a 35-year period.
The new golden age of eclipses, a recurring treat for millions of American, begins with the first event on Aug. 21, 2017. To learn more about what to expect and how to prepare, here's everything we know so far.
What exactly is a total solar eclipse?
Unlike a lunar eclipse, when the moon passes behind the Earth's shadow, a solar eclipse occurs when the moon passes between the Earth and sun and casts its shadow on the planet. As shown in the illustration above, this shadow is comprised of two concentric cones –– the larger penumbra, which from Earth only shows the sun partially blocked, and the much smaller umbra, which blocks the sun completely.
According to NASA, the umbra shadow "barely reaches the planet's surface" and is only about 30 Earth diameters long.
It's been 99 years since the last 'Great American Eclipse'
The last time a solar eclipse crossed from coast to coast in the U.S. was nearly a century ago on June 8, 1918. At the time, the largest city to bear witness to the phenomenon was Denver, Colorado, which had a population of just over 250,000.
Many Americans in the path of the eclipse were well aware that they were watching a once-in-a-lifetime event. The Topeka State Journal noted (twice) in its write-up on June 8 that such an celestial wonder would not take place for another 100 years.
Unfortunately for most skywatchers, conditions didn't completely cooperate. Observatories across the country recorded mostly cloudy conditions.
The path of totality is just 70 miles wide
While the eclipse will be visible across all of North and Central America and the northern half of South America, only those within a narrow, 70-mile-wide band stretching from Oregon to South Carolina will witness totality. (Check out NASA's interactive eclipse map for a closer look at where and when the band will be.) This is due to the moon's umbra narrowing significantly as it falls upon the Earth.
For those within this band, some pretty magical things will take place should the weather cooperate. During totality, planets and stars will suddenly appear in the sky, crickets may start chirping, and birds will fall silent. The sun's corona (which features average temps of 1.8 million degrees Fahrenheit) will become visible, with tongues of fire potentially glimpsed at the edges.
"It is impossible to be a passive observer," writes eclipse enthusiast Dr. Kate Russo. "You do not simply see a total eclipse. You experience it. You are immersed in it. You are completely overwhelmed by it. Many people say that the experience of totality changes their lives."
The action starts on a beach in Oregon
The community of Lincoln Beach, Oregon will be one of the first pieces of dry land to receive the moon's shadow on Aug. 21. (Photo: Swanny Mouton [CC BY-NC 2.0]/Flickr)
The first 28 minutes of the eclipse will occur over the Pacific Ocean, with totality finally making landfall on the Oregon community of Lincoln Beach at 10:16:01 a.m. (PDT). At this point, the moon's shadow will be racing along the Earth's surface at an estimated average speed of 2,251 miles per hour. For the next three hours, the shadow will move across the U.S. towards South Carolina.
You'll need special glasses to view it
Special eclipse glasses, which filter out harmful infrared, ultraviolet, and intense visible light, are required accessories for proper viewing of a solar eclipse. (Photo: Ken Lund [CC BY-SA 2.0]/Flickr)
As we're likely all aware, looking at the sun is a painful experience. On Aug. 21, millions of people will be craning their necks towards our nearest star to glimpse the solar eclipse, but be warned: DO NOT DO THIS WITHOUT SPECIAL GLASSES. Certified "Eclipse Glasses" filter out 100 percent of harmful ultra-violet, 100 percent of harmful infrared, and 99.999 percent of intense visible light.
While those in the narrow path of totality will have the safe opportunity to view the eclipse for a few minutes without safety glasses, everyone else should wear them at all times. The good news is, they're cheap and available for order from a variety of reputable sources. Click here and here to view some options.
Totality will last over 2 minutes
Those within the center of the narrow band can expect an average totality of over two minutes, with the longest duration of 2 minutes and 41 seconds occurring over Hopkinsville, Kentucky. The further you move away from the center, the shorter the length of totality. For example, Bowling Green, Kentucky, which lies just over 60 miles to the northeast of Hopkinsville, will witness a totality duration of only 1 minute and 2 seconds.
The longest possible duration for a total solar eclipse is an incredible 7 minutes and 32 seconds. Unfortunately, for nearly all of us alive at the moment, an eclipse with the potential to hit the 7-minute mark won't occur until June 13, 2132.
The timing of the eclipse favors good weather
A weather map showing the percentage of average cloud cover across the U.S. for Aug. 21. (Image: Jay Anderson [public domain]/Eclipsophile)
While anything is possible, August is about as good for stable weather in the U.S. as eclipse watchers could hope for.
"The summer thunderstorm season is winding down and retreating southward; the Arizona monsoon is breaking; and the storm-carrying jet stream has not yet begun its journey southward from Canada," writes Eclipsophile. "The dry and generally sunny fall season is about to begin."
According to the site, measurements of average sunshine for August along the eclipse track show a 60 percent probability for clear skies.
But eclipse hunters will want to remain mobile just in case
A pair of eclipse watchers takes in the view from Iceland in 2015. (Photo: Universe Awareness [CC BY 2.0]/Flickr)
For those who have been planning for this event for months or even years, having a backup plan is wise.
"Pick a location with a good and uncrowded highway system that you can use to relocate the day before, the morning of, or the hour before the eclipse if weather threatens," advises the site GreatAmericanEclipse.com. "The total solar eclipse will be such a spectacle that you won’t regret making the effort to find a clear viewing location."
Other recommendations include bringing camping gear or making hotel plans that are easily cancelled should adverse weather become more of a possibility as the date approaches.
If you'll be eclipse-hunting, NASA would like your help. The agency is asking citizen scientists to collect cloud and air temperature data and report it to them via a free app on your phone called GLOBE Observer. (GLOBE stands for Global Learning and Observations to Benefit the Environment, a research program that encourages the public to collect and analyze environmental observations.)
Be advised that the eclipse path goes through rural areas where cellphone service is spotty at best, and it'll be even worse with swarms of eclipse fans trying to post to social media. Verizon, AT&T and Sprint plan to temporarily boost capacity in some places with portable towers, the Washington Post reports.
It will be livestreamed –– from 100,000 feet
A view of a solar eclipse at 35,000 feet as captured by Alaska Airlines in March 2016. (Photo: Alaska Airlines/YouTube)
If you're nowhere near the narrow band of totality, don't feel like traveling, or find yourself stuck under cloudy skies, the next best option is available online.
NASA has partnered with video platform Stream to pull off an unprecedented livestream of the eclipse using a network of 50 high-altitude weather balloons equipped with cameras. Drifting at an average altitude of 100,000 feet, these balloons will offer a view of the August eclipse unlike any other. According to Stream, this livestream event is expected to be viewed by more than 100 million people.
If you miss it, the next one is only 7 years away
The Great North American Eclipse will take place on April 8, 2024 and will cross diagonally from Mexico to the U.S. and to the maritime provinces of Canada. (Map: Michael Zeiler/www.greatamericaneclipse.com)
Should the world conspire against you on Aug. 21, your next opportunity to view a total solar eclipse in North America will mercifully arrive only seven years later. On April 8, 2024, the Great North American Eclipse will track from Mexico over major U.S. cities like Austin, Dallas, Indianapolis, Cleveland, Buffalo, and into Canada. The average duration of totality within the umbra is expected to last just over four minutes.
Editor's note: This story has been updated since it was originally published in April 2017.