No matter where you are in the contiguous United States on Aug. 21, if skies are clear, you'll see something that hasn't been glimpsed since 1918 — a solar eclipse visible across the country from coast to coast.
But what if you're not on the ground? What if you happen to be in midair on an airplane during the total solar eclipse?
Unfortunately, the outlook for seeing the disk of the sun directly isn't good if you're traveling on a commercial flight, experts told Live Science. However, with a little calculation, you can figure out whether the effects of the eclipse will be visible on the clouds around you or on the ground below. And some lucky flyers may find that they're crossing the eclipse's path at just the right moment to experience the dark shadow of totality (when the moon's shadow completely covers the sun), experts said. [NASA's Total Solar Eclipse Maps (Photos)]
Only those in the path of totality — where approximately 12 million people live, though many will be traveling there to view the celestial event — will experience the dramatic daytime darkness of a total eclipse. In other parts of the country, daylight could fade to a near-twilight dimness, depending on how much of the sun is blocked by the moon.
A special Alaska Airlines charter flight is scheduled to "chase" the eclipse, Alaska Airlines representatives announced June 26 in a statement. The flight, which is not available for commercial booking, is scheduled to take off at 7:30 a.m. local time and will carry astronomers and eclipse enthusiasts off the coast of Oregon and over the Pacific Ocean, to catch sight of the eclipse before it begins its journey across the mainland of the U.S., Space.com reported.
"Flying high above the Pacific Ocean will not only provide one of the first views [of the eclipse], but also one of the best," Sangita Woerner, Alaska Airlines' vice president of marketing, said in the statement. (Apparently, the sun will be rising just at the time the solar eclipse "touches down" at 9:48 a.m. PT, or 16:48:33 UTC, meaning the sun will rise while it is completely eclipsed, according to Eclipse2017.org.)
Many people who have commercial airline flights scheduled for Aug. 21 may also find themselves in the air while the eclipse is underway. If you're one of those people, what might you see if you're flying over a part of the country experiencing a partial eclipse? And what could it look like if you're crossing the path of totality while the eclipse is at its peak?
It's all about the angle
Being able to see an eclipse from the air depends on the angle of the moving sun relative to the airplane, and by the time the Aug. 21 eclipse begins, the sun will be too far overhead to be visible from an airplane window, meteorologist and Space.com skywatching columnist Joe Rao told Live Science.
In 2016, Rao was a passenger on Alaska Airlines Flight 870 during a total solar eclipse, which reached its maximum when the sun was about 10 degrees above the horizon. This year, when the show begins for people on the western coast of the U.S., the sun will be significantly higher in the sky — about 40 degrees above the horizon, Rao said.
At a typical flight altitude of around 35,000 feet (11 kilometers), airplane passengers seated on the plane's "sun side" might be able to glimpse the sun only if its height above the horizon is no more than 30 degrees, Rao told Live Science.
Unfortunately, this means that the angle of the sun's position during the Aug. 21 eclipse will make it impossible to see through a window of a commercial aircraft, "even if you are contorted to have your nose pressed up against the bottom of the window from a 'sun-side' window seat," Glenn Schneider, an astronomer with the Steward Observatory at the University of Arizona, told Live Science in an email.
For the Alaska Airlines eclipse flightscheduled for Aug. 21, Rao has advised airline officials to fly the plane 1,000 miles (1,609 km) off the Oregon coast, in order to catch the eclipse over the Pacific Ocean when the sun will be around 25 degrees above the horizon, he told Live Science.
Schneider, who also worked with Alaska Airlines to determine the best course for their eclipse charter flight, explained that the custom flight path "was defined to fly across, not along, the moon's shadow, to put the sun at the right azimuth [angle] to be visible out the aircraft's right-side windows," he said. [The 8 Most Famous Solar Eclipses in History]
Light and shadow
But even if you can't see the sun directly from an airplane, depending on where you are in the sky during the eclipse, you might still be able to see a change in the light around you if the sun is partially blocked by the moon, an effect that Rao described as "counterfeit twilight."
"It's not the kind of twilight that you see when the sun goes down," Rao said. "It's just strange — in the sense that the quality of light is different from what you're usually accustomed to seeing. It's kind of like putting on a pair of polarized glasses; there's a metallic-like color to the sky," he said.
The more that the sun is covered, the more dramatic that view will be, Rao told Live Science. And those on certain flights may find that their path aligns enough with the movement of the moon's shadow, enabling them to experience the drama of totality.
"You'll definitely notice once we get past 80 to 90 percent, the inside of the cabin is going to be getting darker," Rao said.
"It's going to be like curtain time at a Broadway play in the 30 seconds before totality —that light's going to dim down very quickly," Rao said.
However, finding yourself on a flight crossing the eclipse path at the precise time of totality is "a real long shot," Schneider told Live Science in an email.
Calculating your path
If you're scheduled to be on a commercial flight while the eclipse is underway, how could you find out where your flight path and the eclipse's path might intersect? Your best course would be to consult the flight-tracking website Flight Aware — which provides moment-by-moment flight data — and look at past flights along that route to estimate your plane's latitude and longitude positions while in the air, Rao told Live Science.
"I would look at the history over the last 10 days of that flight I'm going to be on," Rao suggested. "I would try to draw some kind of a mean or average of where the plane usually is — or where it has been over the last 10 days — and then try to match it up against the totality path," he said.
By comparing the timing as well as the longitude and latitude positions of the airplane's flight path to similar coordinates along the eclipse path — available through an interactive map produced by NASA — fliers can estimate how much of the sun might be covered at a given point during their travels, Rao explained.
"If it's more than 70 percent, you'll notice it if you're looking out the window of the plane," he said. "The clouds will appear yellow or amber in color instead of bright white, because the light that comes from around the edges of the sun has a different quality than the light when the sun is not eclipsed."
Those who find they are flying close to the path of totality — though not directly in it — may see the moon's shadow projected on the clouds nearby or even on the ground below the airplane, a sight that is "quite remarkable," Schneider said. From a typical commercial flight altitude of about 35,000 feet, the horizon is about 200 miles (320 km) away, "so you can see quite a distance, and you could get lucky in that regard," Schneider said.
"Hopefully, there'll be enough of the sun covered that you'll be able to notice something out of the ordinary, something different from what you would normally see during a flight," Rao added.
REMEMBER to never look directly at the sun during a partial eclipse. Make sure to wear protective eclipse-viewing glasses (sunglasses won't cut it).
On Aug. 21, Live Science reporter Mindy Weisberger will be sending eclipse updates while on a commercial airplane flying from Los Angeles to New York City, departing at 8:25 a.m. local time. Will there be visible evidence of the eclipse from midair? Follow Live Science on Facebook and Twitter to find out!
Original article on Live Science.