I had never seen the Aurora Borealis before. And I was really hoping to get a little sleep on the long flight to Paris, France a couple months ago. Five hours out of San Francisco, halfway to Europe, the sunset changed the hue of the sky from cloudy and blue, to pink, then to midnight blue and on to black. Clouds had obscured much of the United States and Canada on the flight, and I wasn't planning on a night of stargazing. I was studying and practicing my French phrases. I looked out my window, facing north. I was flying with Cassiopeia! I felt like I could step right off the plane and float towards the Queen of the winter sky, Cassiopeia and Andromeda's heroic rescuer and lover, Perseus. The moon wouldn't be rising for hours, and we would have landed by then anyway. Bright Algol, the Demon star was just on the other side of my window.

Mesmerized, I shielded my eyes from the light. Luckily many passengers were sleeping. The only light came from the wing of the plane. There are about 30 clusters scattered in Cassiopeia. I saw many of them with and without binoculars, like sparkling tiny diamonds glittering againsts a black velvety darkness, the crown jewels round the neck of Queen Cassiopeia. Magnitude 2.3, MK standard spectrum F2 Caph, is very near the zero-hour line, or the prime meridian of the sky. This line runs from the North Galactic Pole, near Caph, to Alpheratz , (21 Alpha Andromedae), onwards to Algenib (88 Gamma Pegasi). Lower still it intersects with the ecliptic in Pisces. M52 (NGC 7635) in Cassiopeia, was just below Caph tonight. The "W" shape vertical or straight up on its toes like a ballerina. The brilliant cluster, discovered by Charles Messier in September 1774 shines at an easy to see magnitude 6.9. NGC 7789 on the other side of Caph was visible too. The Perseus double cluster, NGC 869 and 884, Trumpler 13r class clusters were very bright, friendly reminders that our planet Earth is a small and insignificant pale blue dot against the majesty of the universe.

I was busily sketching my observations when I noticed a new glow. Not the familiar pristine starry river of light, composed of the rich star fields in this spiral arm of our Milky Way Galaxy, this river was much more fluid. The glow looked like a curtain of light, waving in a brisk breeze. It shimmered, it glowed, it flamed. It was the Aurora Borealis.

I pressed the little button to call a flight attendant. When she arrived, I exclaimed, "I can see the Aurora Borealis; would you please ask the captain what the latitude and longitude is?" She and the other flight attendants all raced to the windows to have a look. Oohhs and Aahhs could be heard over the bass hum of the engines. The light show was addictive. A few minutes later she came back to tell me we were at Latitude 62N, Longitude 93W. It was 10:15 PM Eastern time. We were flying over Hudson Bay less than 10 degrees from the Arctic Circle. I craned my head to the southward, behind me to see how far the Aurora Borealis stretched. It stretched all the way to the Pleiades! Now that's about 50 degrees long, twice as long as the distance between Dubhe - the pointer star in Ursa Major and Polaris in Ursa Minor. It was as wide as Cassiopeia, and that's about 15 degrees. The arching flames of light spiked like a geologic seismograph recording the big one. The flame spikes reached above and below the 15 degree thick curtain of light doubling or even tripling the width of the shimmery green curtain.

What exactly is the Aurora Borealis? And why did I see such a display? I was flying very close to the Earth's North Magnetic Pole, the very best place on Earth (or above Earth, in this case) to see the "Northern Lights". They are more strongly visible here. Aurorae can take on many forms, from a haze near the horizon to arcs, with towering rays above. Sometimes curtains appear. This is how it looked to me. The Aurora is the effect of solar magnetic activity, and the aurora tells us a lot of information about our own sun, as well as something about our upper atmosphere. When electrons and protons from space collide with atoms and molecules of the upper atmosphere, some particle energy converts to radiation like a neon sign. The resulting auroral light appears as a diffuse glow, an arc, band, ray or veil - or a mixture of all of these. Between 50 and 150 miles above the Earth's surface the color is mostly green, but the aurora may be white, yellow or blue. Below 60 to 50 miles, the lower border may have a red fringe border. From 150 to 370 miles above the Earth, the hue is red.

The polar aurora comprises two oval haloes around the magnetic poles. The earth turns under the ovals. The auroral zones are the regions where the aurora is most commonly seen - the areas swept by the night sides of the ovals. The transient aurora is linked with solar flares and appears first as a glow on the horizon in the direction of the magnetic pole. The recurrent aurora derives its source from the high-speed particle streams emanating from persistent sources on the sun such as coronal holes. As the sun rotates, the flow of particles re-encounters the Earth. The particles causing the aurora follow the interplanetary magnetic field lines, which connect either with the Earth's field lines in polar regions or with the magnetotail, when the particles become trapped in the plasma sheet. In an auroral storm magnetic energy is converted into kinetic energy and particles in the plasma sphere are injected into the atmosphere to form the aurora. Auroral light contains only distinct emission lines, brightest in the red end of the spectrum. It is the variable sensitivity of the human eye with color that causes the green emission line of oxygen to appear the brightest.

My celestial night-movie was ending and the earth was rotating sun-ward, our 767 racing for its date with daylight. Dawn was making a pink floating layer on the curved horizon of our planet Earth. I was ready now to experience the the city of light, Paris!