How I Calculated Where the Solar Eclipse and My Plane Would Intersect

I recently visited Southern California with my family. But unlike a typical summer vacation, I spent a good portion of my time counting down the days to our return flight to New Jersey, because that flight was scheduled for Aug. 21 — at the height of the Great American Solar Eclipse.

When I booked the flight, I wasn't sure what kind of eclipse experience we could expect. We were taking off from the West Coast early in the morning — hours before the eclipse touched down in Oregon — but the fast-moving eclipse would overtake us at some point around the central United States.

Where and when would that happen, and what would we see when it did? [Best Photos of the 2017 Great American Solar Eclipse]

Before our trip, I spoke to eclipse-chasing experts, and my hopes of seeing the ultimate midair eclipse view — the sun's disk going dark and twilight extending around the horizon in all directions — were quickly dashed. By the time the eclipse reached land (beginning at 10:15 a.m. local Oregon time), the angle of the sun would be too steep to see it directly from the window of our plane, they told me.

"The geometry and circumstances of [the] eclipse are really not in alignment with the constraints of viewing out commercial aircraft windows across the U.S.A.," Glenn Schneider, an astronomer at the Steward Observatory and the Department of Astronomy at the University of Arizona, told Live Science in an email.

For a typical commercial flight at an average altitude of 35,000 feet (11,000 meters), the sun's disk may be visible through a window until it reaches an angle of about 30 degrees above the horizon. For our flight, the sun would be between 40 and 50 degrees above the horizon — impossible to see from our seats, according to meteorologist and Space.com skywatching columnist Joe Rao.  

"The only way for you to see sun during the flight would be for pilot to bank the plane 20 to 30 degrees — which he's probably not going to do," Rao said.

An indirect view

Glimpsing the sun itself was not going to happen. So, what were our options? Our plane and the eclipse were both traveling across the U.S. — the eclipse tracking to the south and our plane tracking to the north. The precise position of the eclipse from moment to moment was already mapped on NASA's website; if we could plot the timing and position of our flight path using data from past flights on the same course, we could figure out when and where we would intersect the eclipse's path, Rao explained.

However, our chances of that intersection coinciding with eclipse totality, though not impossible, were "extremely slim," Schneider said.

There was a small likelihood that we would be close enough to the path of totality to see the moon's shadow projected on the clouds or ground, but that was also a bit of a long shot, Schneider said.

What seemed more likely was that we would pass through a zone where the sun was blocked more than 70 percent, which would be enough for us to notice a significant change in the light coming through the airplane windows, Rao said. [10 Solar Eclipses That Changed Science]

Calculating our course

Our flight — Virgin America 162 — was scheduled to depart Los Angeles International Airport (LAX) at 8:25 a.m. PT, landing at Newark International Airport (EWR), at 4:52 p.m. ET. A few days before the eclipse, I checked the flight-tracking website Flight Aware, and found the latitude and longitude coordinates for a Virgin America flight path from LAX to EWR, using the flight track log for a plane that had flown the same path the week before, as reference.

According to the log, by 10:15 a.m. PT — eclipse start time — our flight would likely be over the Rio Grande National Forest in Colorado, at a longitude near 37.9177 degrees north and a latitude near -106.5321 degrees west. The eclipse wouldn't be at its maximum there until around 10:44 a.m. PT (11:44 a.m. local time), according to NASA, so we wouldn't see anything just yet.

The eclipse would probably begin to catch up with us as we flew over Kansas. At 12:51 p.m. local time, the plane would be at a longitude of about 39.0106 degrees north and a latitude of about -99.9218 degrees south — and the eclipse maximum in that area would be arriving at 12:55 p.m. local time.

Coding a path

With hours to go before the flight, my programmer husband offered to code a JavaScript "calculator" to visualize where our plane and the eclipse would cross paths. He charted two paths using the anticipated start and end times of our flight, and the times when the eclipse was going to be first visible on the northwestern coast (10:15 a.m. local time) and when it would last touch land on the southeastern coast (2:49 p.m. local time). He used Eastern Time as the standard, and incorporated Google Maps into the program so we could see where the paths would intersect.

But something in the code wasn't working — though our intersection point and time on the map appeared correct, the text readout describing the latitude and longitude were off. He suspected that he needed to factor in the curvature of our path through the air, which there hadn't been time enough to do. Still, we had a pretty good idea of where we would be and what time we might notice the eclipse's effect on the light around us.

Our flight's departure ended up being delayed by 25 minutes, putting us in the air at 9:06 a.m. PT. Even with the short delay, we had a couple of hours before we could expect things to start getting interesting. [Can a Solar Eclipse Really Blind You?]

Dimming down

Naturally, I claimed the window seat, and 2 hours into the flight, I was lifting the shade every 10 minutes or so to check for signs of the impending eclipse. Around 12:51 p.m. local time, as we flew over southern Kansas, I saw the first sign of something unusual — the clouds that were closer to the plane were looking noticeably darker than clouds that were farther away on the horizon, which still appeared bright white.

While it didn't seem to be getting darker, the glare that typically accompanies daytime flights during good weather was gone — I opened the window shade wide and didn't have to squint at all. By 1:06 p.m. local time, as we reached 37.9464 degrees north and -99.0358 degrees west — still over southern Kansas — there was solid cloud coverage beneath us, and the light was warmer than usual, as though the window were covered by a polarizing filter that had dialed down the clouds' brightness to a comfortable viewing level.

At these approximate coordinates, eclipse maximum occurred at 1 p.m. local time, according to NASA's interactive eclipse map.

My eyeballs could feel the sun emerging from behind the moon as the eclipse's shadow sped past us and the light gradually strengthened. By 1:12 p.m., the clouds were growing whiter, and by 2:26 p.m., I had to close the shade against the glare. And just like that, the eclipse was over — for us, at least.

After that, the eclipse and our plane continued on our separate ways — us to New Jersey and the eclipse to its final point over land near McClellanville, South Carolina, where it appeared at 2:46 p.m. ET. Our view might not have been as dramatic as those documented from the ground, but it was still a fascinating perspective on a historic cosmic event. I expect that I'll remember that unusual light every time I sit beside an airplane window, lift the shade, and have to shield my eyes against the brightness of the unobstructed midday sun.

Original article on Live Science.