Here Comes the Sun
By John Mangels
Science Communications Officer
On Monday, August 21, 2017, residents of the continental United States will experience a celestial spectacular that hasn’t happened in most of our lifetimes.
During 90 minutes, the moon’s inky shadow blocking the sun will race completely across the country at nearly 1,100 miles per hour — a coast-to-coast total solar eclipse from Lincoln Beach, Oregon, to Charleston, South Carolina.
Partial, total and annular solar eclipses (the latter is when the moon passes directly in front of the sun but is too far from Earth to entirely obscure it, leaving a visible outer ring called the annulus), are periodically visible in parts of the U.S., depending on the particular orbital alignments of sun, Earth and moon. Residents of five Northwestern states saw the last total solar eclipse visible anywhere on the U.S. mainland, way back in 1979. Hawaii experienced one in 1991.
But the last time a total solar eclipse transited the entire continent, from the Pacific to the Atlantic coasts, was nearly a century ago: June 8, 1918. World War I was still raging, airmail service had just begun and the Cleveland Museum of Natural History wouldn’t be founded for another two years.
In the upcoming August eclipse, the path of totality — the 70-mile-wide band of deep shadow where the moon will completely hide the sun — will track across 14 states spanning the country. Weather permitting, the rest of the nation (except Hawaii and northern parts of Alaska) will witness at least a 50 percent eclipse. In Cleveland, we’ll see 80 percent of the sun obscured, beginning at 1:06pm, peaking at 2:31pm and ending at 3:51pm.
Its broad accessibility is one thing that makes this eclipse so exciting.
“You usually have to travel extreme distances and spend a lot of money to see a total eclipse of the sun,” says astronomer Clyde Simpson, Manager of the Museum’s Ralph Mueller Observatory and a veteran of several of those trips. “This is a wonderful, rare opportunity where you don’t have to go very far to see one of the grandest spectacles in nature.”
“Almost everybody in the country is no more than 12 to 14 hours away from the path of totality,” adds astronomer Jason Davis, Manager of the Museum’s Nathan and Fannye Shafran Planetarium.
Streamers, Beads and Diamonds
What they’ll see will be amazing.
If there’s a clear view of the horizon, eclipse-watchers may catch the moon’s shadow rapidly approaching from the west, like an onrushing tidal wave.
In the sky, in the last few moments before the moon completely blocks the sun, the sun’s rays will stream through the gaps between the moon’s mountains and its rugged impact crater rims. Those dazzling points of light, resembling a necklace of beads around the dark circumference of the moon, are called Baily’s beads, named for the British astronomer Francis Baily, who vividly described them to Royal Astronomical Society colleagues after observing a solar eclipse in May, 1836. Baily reported that the beads of light appeared to flow and coalesce, like drops of water.
“The last Baily bead that you see makes the image of the eclipsed sun look like a ring with a brilliant diamond on it,” Simpson says. “The diamond ring effect is stunning.”
Other startling effects as the moon completely blocks the sun for roughly two and a half minutes are the sudden temperature drop (from daytime to nighttime levels in seconds), the bursts of gas and magnetic energy called coronal streamers that are visible in the sun’s outer atmosphere, and the disconcerting shifts in light, color and shadow on Earth.
“As you approach totality, two things happen,” Simpson explains. “First, the light is really weird. It turns flinty. You know that as you approach twilight, the colors start to diminish. With an eclipse, likewise. It’s like an overcast day, but the difference is you still have dim sunlight with clear skies. It’s jarring.”
Second, as more and more of the sun’s face is obscured by the moon, its light-emitting shape changes from a 360-degree disk to a thin crescent sliver. That alters the nature of the shadows cast by objects such as trees or people. During the lead-up to the eclipse, shadows become sharper because they’re being generated by a shrinking slit of sunlight rather than a large orb. It’s like the difference between standing under a ceiling full of fluorescent lights verses a single spotlight.
“The contrast is very high because those shadows are so strikingly sharp,” Simpson says. If it’s a perfectly clear day, it’s unsettling. And just a couple of minutes before totality, you can see the bright stars and planets coming into view while the sun is still out. I always feel like I’m in some strange science fiction movie.”
Getting to the Totality Zone
The best way to view the eclipse safely and in ideal conditions is with the guidance of professional astronomers. Whether eclipse-watchers want to travel to the totality zone or remain in Northeast Ohio for the partial effect, the Museum’s astronomers can help.
Davis and Astronomy Education Coordinator Nick Anderson will lead an
overnight bus trip for Museum members to the eclipse’s center line in Kentucky, departing on Sunday, August 20. Cost is $475 per person and includes overnight hotel lodging in Glasgow, Kentucky, as well as instruction on how to view and photograph the eclipse.
For those remaining in the Cleveland area for the partial eclipse, Simpson will be operating the Museum observatory’s refracting telescope, allowing visitors to safely observe a projected image as the moon crosses the sun’s face. To learn about other Northeast Ohio eclipse-viewing opportunities, follow the Museum’s astronomy Twitter feed,
@CMNHastronomy.
And in June, July and August, leading up to the big event, the Museum’s Shafran Planetarium will feature
programs for children and adults explaining how eclipses occur and how to safely view them.
More Awesomeness to Come
As a student in 1994, Davis stayed home from school and fashioned a box into head-mounted pinhole camera so he could watch the annular eclipse visible in the Midwest and Northeast. Now he’ll be helping others share a similar experience. “I thought it was great back then,” he says, “but I’m absolutely certain that this year’s total eclipse is going to erase that memory completely.”
And Davis, Simpson and Anderson are already looking forward to April 8, 2024, when the center line of the next total solar eclipse will pass directly through Cleveland.
“For a given location on Earth, you can anticipate a total eclipse of the sun about once every 350 years,” Simpson says. “We’ll hit the jackpot in 2024.”
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