Fri, 29 Feb 2008

Skywatching

There are fewer sights more humbling and more inspiring than the night sky on a dark, clear evening. These days, though, it is increasingly difficult for people to see the skies as our ancestors did. In much of the so-called civilized world, thanks to urbanization and suburbanization, the night sky is rarely a dimensionless, absolute black hemisphere punctuated by pinpoints of light spread out like tiny diamonds on black velvet. The pale yellow glow of sodium-vapor streetlamps, glaring skywards as much as downwards, gives much of the sky a washed-out aspect, with only the brightest and most obvious stars and constellations usually visible.

One of the more impressive sights that planetarium shows from my youth liked to display was a kind of before-and-after view of the night sky: first, what we would normally see in the sky several hours after sunset (when visiting the Hayden Planetarium in New York City, their projected view even from a relatively dark area like Central Park always shocked me -- so few stars!). Then, after the unspoken but unmistakable "So what?" reaction, they'd crank up the giant ant-shaped Zeiss projector in the center of the floot to show off what it could really do: "But if you were to go far out into the country, away from the lights of the cities, the sky would look like this.... And after a momentary pause, the projected image of the cosmos overhead would be revealed in all its glory. (There were always a couple of "Oohs" and "Aahs" at this point.)

Probably one of the things that distinguishes human beings from the other creatures that walk the earth is our sense of wonder. And there can be little doubt that one of the very first sights that the earliest humans looked upon in wonder was the night sky. While the winds blew and the rains fell and the seasons changed all around them, there was a kind of permanence about the stars in the sky. Like the sun and moon, they rose and set, but always their relative positions stayed the same. (A few of them strayed from their assigned places over the course of the weeks and years -- these were eventually called planets, from the Greek planasthai, which means, "to wander".)

Over time, people watched the movements of the stars, and came to realize that their was a regularity, a predictability to their motions across the sky. The presence or absence of certain constellations in the sky marked the beginning or the end of the seasons. Very practical things like when to plant and when to harvest could be anticipated and planned for in advance. The exact dates of religious festivals could be accurately known and scheduled. The notion that the infinitely vast cosmos was something that human beings could know, and understand, and put to use, was one of the first great intellectual breakthroughs in human history.

Having determined that the stars were regular and predictable, it was only natural for people to start to apply that knowledge in a practical, technological way. Some of the earliest and oldest archaeological sites we know of are of structures that serve to make astrological calculations: Stonehenge is probably the best known of these, but there are many others found all over the world, in Africa, the Americas, Asia, and elsewhere in Europe. The need to understand the passage of time, and to master the movements of the stars that formed the basis of that understanding, was clearly a universal human desire.

While there was a great regularity to the movements of the stars, occasionally there were other events happening in the skies that could not be so easily explained. Once in a great while, a star would either appear out of nowhere, or one would suddenly increase tremendously in brightness for hours or days or even weeks at a time. Some of these unexpected visitors would grow long, luminous tails that arced across the night sky. These would also come and go, but were they harbingers or omens of important events to come? Kings, Princes, and Potentates almost all thought so, and demanded that those who watched the skies and kept their calendars be able to predict these odd phenomena -- or at least have a plausible explanation of what their appearance and disappearance meant. (The consequences of not being able to do so were, on occasion, severe.)

Some of the most difficult things for these early astronomers to predict were eclipses. Stars and planets were obviously important, but they were also mere points of light in the sky compared to the sun and the moon -- the sun the source of light and warmth by day, the moon the bringer of tides and the measure of the months and seasons. They were huge, and thus hugely important. Any force that was so powerful as to be able to mess with them was clearly not something to be taken lightly.

The more dramatic of the two was the solar eclipse, with the bright disk of the sun going partially or even completely dark. This was powerful stuff, and thus offerings and supplications were generally in order on those strange days when the sun's disk seemed to be snuffed out, and woe betide the astronomer or astrologer who failed to predict it! Fortunately for them, total solar eclipses are relatively rare in the sense that the path of totality is generally quite narrow and small; it is also true that the more frequent partial solar eclipses are often not easily noticed by casual observers with the naked eye. There was a sporting chance that the powers that be would never see such an event in their lifetime, but for those that did, it was clearly awe-inspiring and terrifying all at once.

Lunar eclipses, on the other hand, occur far more often, and are visible over the entire nighttime area of the earth, and so were far more likely to be part of people's living memory. Even though the full moon never completely disappears during a lunar eclipse, it can become very dark, and it often changes color from the usual yellowish-white to a coppery orange-red. Also, whereas solar eclipse viewers typically experience only a few minutes of totality in any one place, lunar eclipses happen over the course of several hours, allowing additional time for anxiety and remorse on the part of those who did not understand what was heppening.

Over the many millennia people have been watching the skies, increasing sophistication in mathematical calculations and better observing technology helped improve the astronomer's lot. Kepler's laws of planetary motion allowed more accurate predictions of astronomical events, including eclipses. The refracting telescopes pioneered by Galileo were an enormous boon to astronomers, changing the stars and planets from mere points of light to real worlds of their own; the reflector design developed by Isaac Newton brought even more advances, due not so much to greater magnification but to its greatly improved ability to gather light. Even the creation of scientific societies like the Royal Acadamy in England helped advance astronomical knowledge by gathering and then disseminating observations and information on a wide scale.

Thus, even to the present day, eclipses, while their causes are well understood, and their dates and times computable with subsecond accuracy, are still newsworthy events.

I, like so many others, have never seen a total solar eclipse in person. Twice in my lifetime so far I have happened to be living in places where there were partial solar eclipses, where the moon would cross but not completely cover the sun's disk. But even the one which approached seventy percent totality was hardly noticeable to the average person: it's not like the sky became seventy percent dimmer; in fact, the dimming was barely perceptible (no doubt due to the overwhelming brightness of the thirty percent of the sun which remained unobscured). I did do the usual solar eclipse observation tricks of looking at the sun through layers of photographic film, and of using a pinhole in a piece of cardboard to pass the sun's image onto a larger piece of white poster board, and I could clearly see the dark moon chomping a good-sized bite out of the bright sun. But for the most part, these partial solar eclipses lacked any real drama -- no darkness at noon, not even a decent twilight. (I had often thought that if I won the lottery, I would take one of those flights on the Concorde which follow the path of totality for as long as seventy minutes, instead of the usual five or so that ground observers get -- there's nothing like looking at a total eclipse while sipping champagne at 60,000 feet -- but alas, the Concorde is no more. There do appear to be some good opportunities for us Americans to view a total eclipse "at home" as it were, on August 21st, 2017, and April 8th, 2024 -- you can see more specifics here.

Like most people, I have seen my share of lunar eclipses. My wife and I have even taken the kids outside to sit on folding chairs and look through a borrowed telescope at eclipses that took place when they were small. We even managed to troop outside for both lunar eclipses last year. My daughter has participated in the Astronomy Club at her high school for several years now, and so we planned to make the lunar eclipse which took place earlier this month a special event for the family.

Surprisingly, the local high school Astronomy Club didn't have any special activities planned, but another school in the area announced in the newspaper that they would be organizing a viewing with local amateur astronomers at a small airport about twenty miles away. The biggest question was the weather -- the forecast was for overcast and a good chance of snow that evening, and as the evening of the 20th approached, there was little improvement in the outlook. But where we lived, the solid cloud cover was starting to break up, and when the announcement was made that the eclipse-watching session was "go", we bundled up warmly (the temperature was in the mid-20s) and headed off to the airport.

We arrived about half an hour before the eclipse began (around 8 PM), and headed down to the airstrip to join the group already assembled there. I was really rather surprised to see the number of people braving the cold to watch the eclipse -- I estimated about one hundred in all. There seemed to be a large proportion of kids (some as young as four or five) and teenagers in the group, no doubt due to the fact that for the high school Astronomy Club which sponsored and organized the event, attendance was probably compulsory. The weather was continuing to clear, and the expectation was that the skies would be completely clear shortly, keeping the spirits of the crowd high in spite of the cold (at least the winds were calm; otherwise, the night would have been completely miserable).

There were about a dozen telescopes set up for viewing, in a great many sizes and kinds. There was only one "classical" refracting telescope (the kind where you look through lenses down the barrel of the scope) available. I chatted a bit with its owner; he explained that refractors were generally much less popular in amateur astronomy circles, because even with right-angle prism eyepieces, you had to do your observing from the end of the barrel, and unless you had the thing mounted on a very tall tripod, that was generally a less-than-comfortable observation position. But they did have the advantages of being relatively inexpensive, and generally have a fairly high degree of magnification, which were more important for him -- his interest in astronomy was strictly casual, and thus a more sophisticated setup would have been overkill for him.

This telescope was pointed at the moon, and so I took a look at it. The shimmering distortions caused by atmospheric ripples were apparent, but not terribly distracting. What was a little more disconcerting for me was the fact that the familiar face of the moon did not really look all that familiar through the telescope -- until I realized that I was forgetting that refracting telescopes invert their images from top to bottom, so while looking, I had to remember that craters like Tycho, normally far to the south, were appearing at the top of the image, and conversely, the bright northern crater Aristarchus was visible towards the bottom. Once I made the mental adjustment, it was fascinating as always to see the moon in much greater detail than we normally see.

The next telescope I came to was a reflector about six inches in diameter, which meant that instead of lenses, there was a six inch mirror at the bottom of the tube which gathered and reflected the light to an eyepiece mounted near the top of the tube. Because of its improved light-gathering properties compared to refractors, reflecting telescopes are well suited for observing more distant objects, and so this telescope's owner had set it up to look at Saturn, which, coincidently, was located not very far from the full moon that evening.

Out of all the bodies in the solar system, Saturn, with its rings, is the most dramatic, and ostensibly the most beautiful. If first observed it through a telescope while in college thirty years ago, and the sight of it again was still just as moving as it was then. Its pale yellow color only helps emphasize the dramatic splendor of the rings. (The rings change their tilt as seen from earth from well oblique to nearly edge-on and invisible; fortunately for us, Saturn's rings are currently in the "well oblique" stage, and thus very visible.) While it defies logic, when I see Saturn through a telescope, I imagine that I can actually see it spinning like a top. My wife and kids had only seen Saturn in pictures, so I quickly stepped aside to let them have their own looks. And, like my own first viewing of the planet, they each stayed looking at it for a long time, mesmerized by its dazzling appearance. But any extended reveries were broken up by the fact that Saturn kept moving out of the telescope's relatively narrow field of view, which meant that the telescope's owner had to step in and spend a minute or so fiddling with its azimuth controls to get the planet re-centered and back in view. She explained that she was hoping to get a computerized aiming mechanism for her birthday or for Christmas, which would allow the telescope to automatically track an object without having to be manually re-aimed every few minutes. "Now," she added, "all I need is something good to look at for ten or fifteen minutes at a time!" I suggested that Jupiter and its four large moons were always fun to watch, a kind of solar system in miniature -- but unfortunately, Jupiter was not in the visible sky this evening.

Still another reflector was turned at right angles to most of the others. I asked its owner what he was looking at, and he said that he was watching Mars, this evening rising early and so far "ahead" of the moon in its nocturnal track across the sky. While not as large or as powerful as the Saturnian scope, I could clearly make out Mars's rich red-orange color, it's vivid white polar cap, and the darker-colored blotches which entranced Percival Lowell and so many others into believing there were canals on the Red Planet. It was also hard to imagine that there were two infinitesimal specks somewhere in my field of view, the Mars Rovers still managing to scoot around and explore the planet, years past the end of their normal life expectancy. Millions of miles from the airport where I stood, there were a couple of robotic explorers from Earth carrying on with their work, and adding to our store of knowledge about Mars.

The last telescope I looked through during my initial pass among the astronomers was one of the largest homebrewed telescopes I had ever seen. It belonged, fittingly enough, to the high school Astronomy Club which had organized the evening's activities, and had been constructed by teams of students over the course of several years. What it might have lacked in sophisticated controls or advanced optics was more than compensated for by its sheer size: the barrel was nearly seven feet long, and approached three feet in diameter! Yet for all its bulk, it was constructed of fairly light-weight materials (a construction form used to pour concrete columns made up the main part of the body), and it was easily moved into place and kept pointed at the moon. Since well over an hour had passed since we first arrived, the eclipse was now nearing totality, and this was the place to watch it. The earth's shadow now covered much of the moon, changing its color from a ruddy brownish-red on the top left quadrant to a brighter coppery color as one looked towards the bottom right; there was just the smallest sliver of uneclipsed surface glowing bright white against the rest of the darkened orb.

And then, as I was watching, even that was wiped out, and the entire surface was reduced to the brown-red-copper stain that had already overtaken the rest. "It's 10:03 PM," I heard the faculty advisor of the club announce on a portable PA system, "and that means we are now in totality." I took a break from gazing through the telescope so as to not hog the thing from the club members all wanting to see this for themselves, and looked back across the night sky with my unaided eyes. One of the remarkable things about a lunar eclipse is that, when it reaches its peak, a great many stars become visible which are normally obscured by the light of the otherwise full moon in the sky. Details of fainter stars in places like the constellation Orion were suddenly easy to see; after waiting a few minutes for my eyes to adapt, I could even make out the fuzzy patch of the Orion nebula (one wonders if some early human caught sight of the supernova explosion that created it, and wondered about that unexpected flash in the sky).

I took a break at this point and went back into the airport's administration building, which was open as a refuge from the cold, and where volunteers were serving hot beverages and soup. My wife and kids were already inside, having succumbed to the cold some time earlier. I told them that the totality was starting, and that they should get outside some time in the next half hour or so to ensure that they caught the best views. A good part of the crowd had already drifted away, especially those with younger children. I took about fifteen minutes to warm myself up, then led my family back outside so that they could make their own observations. They trooped from telescope to telescope like I had done, looking with wonder at the show unfolding in slow motion overhead.

But they were also cold and it was getting late. The lady who had been watching Saturn all evening decided on one more observation before she began packing up to go, and she pivoted her telescope around and pointed it at the second star in the handle of the Big Dipper. And there, after a little bit of adjustment, my family and I were treated to a beautiful view of a pair of bright blue stars -- the second "star" is actually a binary system, with a fainter companion star orbiting its larger and brighter companion. I was reminded of how, from the time of Galileo on, as our instruments got better and better, the scope and beauty of the universe all around us -- so much of which is inaccessible to our naked eyes -- has been made clear to us: the Hubble Deep Field image (not far from the Big Dipper) shows galaxies upon galaxies, as far as it can see; the Voyager probes are still sending back trickles of data thirty years after their launch, as they approach the boundaries of interstellar space; and how even something as prosaic as a lunar eclipse can bring a family together on a cold evening to marvel at the universe all around us.

Posted Feb 29, 2008 at 19:55 UTC, 3442 words,  [/rich]  Permalink