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Windows 2001 - Beauty Outside your Window!

By Edward Pascuzzi
April 4, 2001

Join us as we take a tour of the sky to view a dazzling array of astronomical and atmospheric phenomena you may see when you fly.

As our Boeing 767-300 began its descent into New York City one recent afternoon, I gazed out my port window and spotted a beautiful sight. Through wispy clouds beyond the wing, a rainbow-like ring encircled the entire Sun, highlighted with brighter patches of light. As an avid astronomer and sky-watcher, I knew I spotted a solar halo adorned with bright patches called sundogs. I immediately asked the cabin attendant to inform the flight crew so as to alert the passengers of the view. Minutes later, the announcement came; "Ladies and Gentlemen, one of our passengers has informed us that a ring and some dogs are visible around the sun outside the left side of the aircraft!" Soon after the comical announcement, a correction was made and passengers were impressed with the view.

Those of us who fly frequently - and take the time to look out the window - have an unparalleled view of the sky and may glimpse such breathtaking events much more often. Phenomena as common as star-filled night skies, rainbows, and eclipses, or as uncommon as aurorae, glories and the green flash, have either atmospheric or astronomical origins. In either case, they illustrate how the complexities of nature can combine to create breathtaking vistas that may be readily visible from your in-flight aircraft.

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Fig. 1) A sun pillar visible at sunset behind the wings of Austrian
Airlines’ A330 OE-LAM over the North Atlantic Ocean.
Photo © Edward Pascuzzi

Beyond the tip of our wing, gazing back at the sunset following our evening departure one may easily notice a faint column of light at the location of sunset (Fig. 1). Caused by the reflection of sunlight off nearly horizontal plate-type ice crystals in our atmosphere, these impressive sun pillars are certainly something to look out for when the Sun has nearly set (or risen). To obtain a good photograph, first be sure to place the camera as close to the window as possible, shade the region around the camera so as to minimize the reflections of interior cabin lighting off the window and then click away, bracketing around 1/30 or 1/60 of a second.

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Fig. 2) A composite image of the United States at night as viewed from 400 miles (640 km) above the ground. Courtesy of the International Dark-Sky Association with data provided by the Defense Meteorological Satellite Program
 
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Fig. 3) Comet Hale-Bopp viewed against a dark, star-filled night sky.

As daylight fades into darkness, our attention wanders Earthward, gazing upon the myriad lights adorning the landscape as far we can see. While many of us are familiar with air, noise, and water pollution, few may be familiar with light pollution; the excessive use of night lighting brought on by technological growth and the quest for advertising space (Fig. 2). Anyone who has ever tried observing the night sky from large urban locations immediately notices the scarcity of stars on clear moonless nights, replaced instead by a pervasive orange-white glow brought on by popular sodium vapor lights. As a result, most urban dwellers can only see a few dozen stars on even the clearest nights. In contrast, those living in rural, open areas will find the opposite to be true, with literally thousands of stars visible as a result of the absence of light pollution (Fig. 3). Interestingly, such a difference will be visible on any night flight you are on, provided interior cabin lighting is completely turned off. While the human eye has the ability to register this sight easily, snapping some photos of such sights from a moving jet will prove futile, as your camera will require very long exposures (several minutes) in order to fill the frame with stars . Thus, such photos are best achieved with fixed cameras situated in dark, ground-based locations.

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Fig. 4) An impressive aurora over New York State, USA,
taken by amateur astronomers Alan and Sue French.


Ask any friend or acquaintance when they last saw colors and electricity in the night sky and you may find yourself sitting alone at lunchtime! Asking the same of flight crews, however, will probably engage you in an invigorating discussion about the Northern Lights, or Aurora Borealis (or, for those Southern Hemisphere flyers, the Southern Lights, or Aurora Australis). At times, the night sky can take on beautiful combinations of greens, reds and blues in a shimmering curtain-like display (Fig. 4). The Sun, in addition to emitting heat and radiation, also spews forth the solar wind, a continuous stream of charged particles. Upon reaching Earth, these particles impact primarily nitrogen and oxygen molecules some 90 to 250 miles up (150 to 400 km), causing these atoms to emit light of various colors yielding the aurorae that we silently witness. Unfortunately, because of their subtly, aurorae, like the star-filled night sky, are not easily photographed from in-flight aircraft, though they are indeed stunningly beautiful and easily visible to the unaided eye.

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Fig. 5) A meteor becomes visible as it streaks through
our atmosphere and burns due to frictional forces.


Due to the passage and continual disintegration of comets through our solar system over many hundreds of years, heating of these "dirty snowballs" by the Sun causes very small bits of them to form in their own solar orbit. As the orbiting Earth passes through this material, miniscule cometary debris falls to Earth, burning up in potentially bright displays of streaks of light, collectively called meteor showers (Fig. 5). Occasionally, a chunk as large as a golf ball or so may flare into many different colors as it passes through our air and disintegrates due to frictional heating. Such rare occurrences are often called bolides or fireballs. Though brief in appearance, bolides occasionally make the news as they may have numerous witnesses, take on a variety of colors and may often be mistaken for other airborne objects. Lasting but seconds, meteors are approximately 30 to 125 miles (50 to 200 km) high, well above any civilian aircraft.

Just as subtle are objects which have been put in the sky by us. From the darkened cabin, the observer may notice an artificial satellite, placed in Earth orbit as a result of our continuous effort to incorporate technology into our “difficult” push-button lives. Satellites appear as star-like objects moving among the stars, sometimes flickering because they reflect sunlight from their irregular shapes as they spin. Interestingly, more than half of all functioning satellites lie at altitudes between about 21,000 and 23,000 miles (34,000 to 37,000 km), with some 7000 non-functioning satellites and more than 50,000 pieces of space junk circling Earth at much lower altitudes. Just in case you were wondering, you can always distinguish a satellite from an aircraft, as they possess no anticollision or landing lights.

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Fig. 6) The Moon during a total lunar eclipse takes on a
strange reddish color as it passes through Earth’s
shadow (also visible in this image is Saturn).


Lastly, one of the most beautiful astronomical phenomena visible during our night flight involves Earth, Sun and Moon. As the Moon orbits Earth, it may at times pass directly into Earth's shadow, preventing sunlight from illuminating its surface. The passenger fortunate enough to view a Full Moon as it passes completely through Earth's shadow will witness a total lunar eclipse (Fig. 6). In such a circumstance, sunlight filtered through our atmosphere still falls on the Moon, lighting it with an eerie reddish glow. Once again, while your eye can easily discern the ruddy color the moon acquires during an eclipse, the camera will require several seconds to a minute to capture the deep red hues seen in photographs.

As our flight makes the transition from night to day, we await the rising Sun at which point the keen-eyed passenger may notice a brilliant grass-green flash of light at the Sun’s location the moment it rises. Visible at sunset as well, the green flash is one of the most famous, noteworthy and infrequently witnessed sky phenomenon. Impressions of this event are found as far back as 1882, when author Jules Verne recounted the beauty of the green flash in his Le Rayon Vert (The Green Ray), describing the color as “the true green of Hope.” Essentially, the underlying cause of the flash arises from the dispersion (spreading or separation) of sunlight by our atmosphere, which acts as a lens. While red and orange light tend to be scattered a great deal at sunrise, green light is scattered much less and appears only briefly at the Sun's rising point, causing the “flash” we see. Since observing the green flash from the ground requires a very clear atmosphere and an unobstructed view straight to the horizon, your chances of seeing it in-flight are much better, provided the aircraft is above clouds, and of course, you're on the correct side of the aircraft!

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Fig. 7) A partial solar halo with a sundog visible outside
the port window of an in-flight jet.


Once the Sun is well above the horizon, many sights may still be visible right outside your cabin window. Should your plane be passing through thin cirrus-type clouds and you have an unobstructed view of the Sun through the haze, blotting out the Sun with your fist might reveal an impressive ring of color around the Sun, very similar to a common rainbow, though fainter (it is important to note that staring directly at the sun without the use of proper solar filters can be damaging to one's eyesight and should thus be avoided as much as possible). Called a solar halo (Fig. 7), this effect arises primarily from the passing of light through hexagonally shaped ice crystals in a manner similar to that described above for the green flash. However, no colors here are absorbed by the atmosphere and, as a result, the halo surrounding the sun should have a red inner portion and a blue outer portion. With care, you may also notice a couple of bright patches of light on the halo which appear to “tag along” with the Sun. Known in mythological times as the “chasers of the sun,” these sundogs (or "mock suns"), can be frequently noticed by earthbound observers best at sunrise or sunset. Sundogs occur at specific points on the halo because of refraction of sunlight through flat based plate crystals of ice at high altitudes. Clearly, the combination of halo and sundogs makes for an impressive display as one flies from place to place!

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Fig. 8) A glory visible from the shadow side of an in-flight
jet, projected onto clouds below the aircraft.


So what if you forgot to book your seat on the side of the jet facing the Sun? No problem! While gazing out the window at your aircraft’s shadow, search carefully for a small rainbow of light around the shadow of the plane on the clouds below. While this feature’s name may imply a heavenly origin, you haven’t witnessed the Almighty outside the plane! Called a glory (Fig. 8), it is a colored halo which is centered exactly on the shadow of your location in the aircraft (called the subsolar point). Before the days of aviation, an effect similar to the glory, called the Specter of Brocken, was witnessed only by mountain climbers when their shadow was projected onto a nearby cloud bank. Just as with the aircraft, their shadow was adorned with a colorful ring of light. Though the full explanation of the glory is actually very complex, the primary effect causing it is the dispersion and diffraction of light around water droplets in the air surrounding the aircraft. Unlike some of the evening phenomena discussed earlier, the glory is very easy to photograph. Just follow your camera’s meter and...shoot away!

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Fig. 9) A breathtaking total solar eclipse occurs as the Moon
covers the Sun, revealing the Sun’s wispy corona. The next
such event will be 21 June, 2001, across Africa.


You may think it a rare and perhaps even an odd circumstance that the interest actually exists for people to book a flight only to watch the Sun "disappear" in mid-flight! Well, not so for New York meteorologist and amateur astronomer Joe Rao and several of his colleagues. In July 1990 they convinced officials at Indianapolis-based American TransAir to modify the flight path of Flight 402 to pass right through the Moon's shadow to witness a breathtaking total eclipse of the Sun (Fig. 9). An avid eclipse chaser, Rao determined that the tail end of this eclipse would be visible roughly between Hawaii and California and correctly reasoned that surely at least one commercial airline must have routes in this vicinity. Sure enough, the most promising was ATA's Flight 402 from Honolulu to San Francisco. To his surprise and enthusiasm, authorities at ATA were delighted to delay the departure of #402 by about 41 minutes just so the L-1011 could fly through the eclipse track's end. Interestingly, Rao and his colleagues flew from New York to Honolulu via San Francisco only to "visit" Hawaii for about an hour and a half! Thanks to sun viewers given to all passengers by Rao and his group, some 360 people gazed in awe as the Sun disappeared completely behind the Moon for but a minute or so. During the event, skywatchers happily photographed the completely eclipsed Sun with exposures up to 5 seconds or so before the it crept out once again. Undoubtedly, this event turned out to be one of the most memorable and impressive in-flight phenomena ever witnessed by the passengers of Flight 402.

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Fig. 10) Two of fifteen images of the setting Sun as it “mushrooms” to meet its “anti-sun” on the horizon.


As we prepare for our descent at day's end, gazing toward the setting Sun may prove exciting as we again witness another "lensing" effect of our atmosphere on our departing star. As described earlier, Earth's delicate blanket of air can alter, distort and rearrange our view of many objects in the sky. In particular, the setting (or rising) Sun may exhibit a number of strange distortions similar to mirages. As the Sun sets, refraction of light through layers of air of varying temperature creates the mirage of a rising Sun (called the anti-sun) that seems to ascend to meet the true setting Sun (Fig. 10). The "two" Suns appear to meet and meld into one setting "mushroom" Sun to offer an impressive solar event. While the anti-sun is easily photographed from the ground using a telescope, a typical SLR may reveal only a hint of the effect. Again, care should be taken to avoid direct observation of the Sun.

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Fig. 11) Alternating rays of light and shadow create crepuscular
rays along which the Ancients postulated water would
return to the sky after heavy rainstorms.


As we approach our destination, you may notice cumulus clouds alternately passing in front of the Sun, casting impressively beautiful rays of light through open breaks in the clouds toward the ground below. Many ancient explanations for how water returned to the sky may have resulted from postulating that these crepuscular rays implied the Sun was "drawing water" (Fig. 11). Crepuscular rays are actually alternating rays of filtered sunlight and cloud shadows which are best observed when the Sun's elevation is low. Notice that the rays appear to converge on the Sun, but that they may, in rarer instances, sometimes appear to extend across the entire sky and would thus be termed anticrepuscular rays.

How many of these atmospheric and astronomical phenomena have you witnessed in your years of flying? Realizing the variety of sky phenomena visible before our eyes as we fly should certainly cause us to become more aware of when, how, and why we see such sights, both on the ground and in the air.

Written by
Edward Pascuzzi

Currently a teacher of Honors and Advanced Placement (pre-college) physics and an avid aviation enthusiast, Ed spent twelve years lecturing and teaching in a major planetarium facility and now brings the curiosities of nature to our youth. Ed also reviews science books, writes occasionally for The Physics Teacher and Delta AirLines’ Sky magazines, and his first book, Astronomy for All Ages, co-authored with astronomy writer Phil Harrington, outlines more than 50 activities for the young at heart who have an interest in amateur astronomy. You can read more about him and what he does at http://www.thephysicsguy.com.

13 User Comments:
Username: 747-600X [User Info]
Posted 2001-04-04 15:39:19 and read 28639 times.

I love this article, I spend my entire time on planes staring out the windows, even at night. Watching the "red ants marching into the night" cars on the roadways can be wonderful.
By the way, that first photo is of an A330, not an A300 as it says!

Username: An-225 [User Info]
Posted 2001-04-04 20:11:28 and read 28623 times.

Very interesting. I'll probably make a presentation in my Weather and Atmosphere class about it.

Username: Dee-see-eit [User Info]
Posted 2001-04-04 22:15:25 and read 28612 times.

Very nice article! Enjoyed a lot and remembered me all the flights and incredible views I had until now.

It is also good to know what kind of interesting people are behind their photos at airliners.net!

Best regards from Barcelona
DC8

Username: Pascuzzi [User Info]
Posted 2001-04-04 22:30:24 and read 28609 times.

Hi 7470-600X and all,
Thanks for your note and glad you enjoyed reading the article. The airliner in Fig. 1 is indeed captioned as an Airbus A330, and it was a *great* flight!

Cheers:)
Ed Pascuzzi

Username: Joe pries [User Info]
Posted 2001-04-05 17:52:01 and read 28562 times.

Ed, that was a great read- people do not realize the importance of physics and sciences and the role they play in our lives, especially in aviation. Well done!

Joe

Username: 747-600X [User Info]
Posted 2001-04-05 19:24:17 and read 28556 times.

...guess I must be dislexic :-)... anyway captions (or my inability to read them) aside, it's a great article. I like the pic.s.

I have a question, if this can find it's way to the author - I thought when the sun streamed through the myst beneath clouds as in that last photo it was called the Tyndall affect after the guy who figured it out. Does this hold any water ;-)?

Username: Pascuzzi [User Info]
Posted 2001-04-05 22:47:24 and read 28548 times.

Hi again 747-600X,

Interesting thoughts!....however, I'm not aware of that effect offhand, but it may very well be so.

Ed:)

Username: Redngold [User Info]
Posted 2001-04-06 04:32:10 and read 28536 times.

Mr. Pascuzzi,

Thank you for your article.

During one of my more recent flights (I believe on NWA from ABE-DTW on a DC-9-30) I watched a sun glory for almost the entire trip. Other people on board were not impressed when I tried to get them interested. Oh well...

I also love to watch developing thunderstorms from the air... as long as they're well out of our flight path.

redngold

Username: B727-200 [User Info]
Posted 2001-04-07 06:49:19 and read 28498 times.

Hmmmm, I always wonderred what the shadow on the clouds was called. I have seen this quite often when flying.

A point of interest, it was mentioned that mountain climbers experience the same thing. Well, so do golfers. When you tee-off early enough so that the lush grass is still wet with tiny droplets and the sun at about 45 degrees in the sky, you get the same affect around the shadow of your head on the ground.

Great article too. I spend all my time with my nose pushed against the window. The latest things I have seen is shooting stars over the Pacific on a MEL-LAX flight.

Rgds,
B727-200.

Username: Ikarus [User Info]
Posted 2001-04-11 21:09:54 and read 28424 times.

I still remember seeing a "glory" like the one described around the aircraft shadow for the first time - 1992, KLM B737-300, I believe. Anyway: I was amazed and thought it the most beautiful sight on earth.
However, I got rather used to it lately, and today I watched one appear and disappear on the alternating cloud cover for at least ten minutes prior to landing - without even a shadow of my former emotions. I considered taking a picture of it, but thought it would be pointless as www.airliners.net would not be impressed, and I know how disappointingly pale and blurry clouds and shades of white generally turn out in my photos...

Well, I have to admit that this article truly reminded me of how interesting a phenomena it is, and I look forward to the next time I see one: I'll be sure to attempt a picture or two....

Great article! It manages to recreate some of the amazement I used to feel for the small miracles in this world. Congratulations!

Regards

Ikarus

Username: Pascuzzi [User Info]
Posted 2001-04-14 00:18:00 and read 28402 times.

Hello Ikarus,

Thanks for sharing your thoughts and interests concerning the glory, and on the article.
In fact, an image from the very same flight whose photo is in the article is actually on airliners.net (image #56459), and was taken from a slightly different angle than the one in the article. Thus, never hesitate to shoot something you believe is impressive that you can share with others; who knows when you'll spot it again?

Also, several photos not in the article or on airliners.net I actually shot several years ago and they depict the glory from a *descending* Delta AirLines' MD80. In the photos, what is most striking, is the fact that as the distance from the plane to the clouds decreased, the glory size remained the same! What did change, as you would expect, was the jet's shadow size. If anyone is interested in seeing these images, please don't hesitate to drop me an email and I'll share them with you.

Thanks again Ikarus for your input. Keep photographing!

Sincerely,
Ed Pascuzzi:)

Username: EGGD [User Info]
Posted 2001-11-10 12:19:20 and read 28257 times.

Hey Ed,

Just read the article (i guess i wasn't interested in them when you wrote this). Its really great, i love looking out for odd weather phenomenon, or just interesting cloud formations and cities on the ground. I remember the first time i can remember flying, and it was cloudy (as some people might know, before this flight i was afraid of flying). We spent ages flying through the cloud, but when we got out of the top onto such a beautiful sight of the top of the clouds, i thought it was the most beautiful thing on earth. Of course it isn't, and i've seen alot of great things since then.

On a Monarch A300 we took off at LGW at sunset, and because we were flying due south to MIR. I was in the middle seat (3-3-3) and on the right the sun was setting and it was very bright, and on the left it was already night time. It was weird, I could see both windows and on the left it was like we were on a night flight, and all the lights were on on the ground, and on the right it was still sunny and all the lights weren't on yet. Truly weird experience, although it wouldn't have happened without the middle seat (although i would've preferred a window seat :D).

Great,

Regards

Dan

Username: Jcamilo [User Info]
Posted 2009-09-01 18:18:44 and read 20280 times.

wow amazing!!!! so interesting!!

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