Because most philosophies that frown on reproduction don't survive.

Saturday, August 26, 2017

In The Moon's Shadow

As MrsDarwin wrote, one of the legs of our recent family road trip was visit Nebraska and see the total solar eclipse.

It wasn't my first time going to try to see an eclipse. My family wasn't much of one for big vacations. To support a family on a planetarium lecturer's salary, my father always worked a patchwork of several side jobs, and since people visit museums and planetariums when they are on vacation, the times when other people were taking time off were often when he was busiest. There was, however, one big exception. In 1991 a total solar eclipse crossed over the tip of Baja California and also the Big Island of Hawaii. The community college where Dad worked agreed to send both Dad and one of the astronomy professors on eclipse viewing expeditions: Dad to Hawaii, the professor to Baja California.

With the college paying for Dad's travel and hotel room, the rest of us just needed plane tickets and other traveling expenses to tag along, and so we spent about a week in Hawaii: hiked through a rain forest, visited the volcano, tasted sugar cane, played on a black sand beach. We did all of the satisfying tourist things. And on the morning of July 11th, we got up early and boarded the buses with the rest of the big eclipse tour group, many of us wearing our eclipse tour t-shirts. (Being a tourist destination already and the only part of the US when the eclipse would touch, Hawaii was loaded with eclipse merchandise.)

They bused us out to an open field before sunrise, and we spread out picnic blankets, set up telescopes and cameras, and looked nervously up at the broken clouds overhead. Through the gaps between clouds, we saw most of the partial phases of the eclipse, but then a few minutes before totality the sun went behind a thick, low, cumulus cloud. Right on schedule the sky got dark. It stayed dark for the four minutes of totality, then it gradually brightened again. Several moments after totality, the sun emerged from behind the cloud.

Of course, the thing about missing the eclipse by such a small margin is that across the island experiences varied quite a bit. For us, it was during totality that the sun went behind a cloud. For others, including the staff back at our hotel, the sun had come out from behind a cloud just in time for totality.

Still, we had at least been in Hawaii. The astronomer who had led the group down to Baja California saw the eclipse, but on the way back their buses broke down, people suffered heat and lack of water, and the astronomer ended up in the hospital for a week with malaria. Perhaps in the end, missing the eclipse was the better part of the deal.

In the following few years, we managed to see partial and annular eclipses. We watched the spectacular comets of the 90s: Comet Shoemaker–Levy 9, Comet Hyakutake, and Comet Hale–Bopp. But we never did see a total eclipse.

My father died in 2006, still never having seen a total solar eclipse. When my faithfully science minded brother reminded me that there would be an eclipse crossing the US in 2017, I decided that I owed it to family memory to try again. The older kids were also agitating for a visit to their friends in Texas, and so the great Darwin cross-country road trip was born.


My Dad used to describe his fatalistic streak as "being Irish", after his mother, who faithfully reared him in the Irish-American experience of the depression even though he was born in 1948. It's not surprising. Grandma was 19 when the stock market crashed in 1929. She came of age in the depression. Her family lost their farm in Iowa and drove out to the West Coast, where her father sold various things door-to-door in order to put food into his children's mouths. Eventually he hit upon selling insurance, and opened the first State Farm office in San Diego. Post-war, this would lead to security and something a bit like prosperity, but by then Grandma's view of the world was already formed.

I have have this fatalistic streak myself. Dad used to tell a story about how Grandma was convinced she wouldn't live past some age (I forget what exactly) in her mid-sixties, for the simple reason that everyone else in her family had died before that age. As it was, she lived into her 90s, but apparently right up until the night before that record-making birthday she was convinced she wouldn't last. Since I knew Grandma as someone who remained alert and tough past 90, this seemed a funny story to me. But now, as someone whose father died of cancer before turning 58, I myself find it hard to imagine that I'll turn 60.

Through some similar sense of fatalism, even as I planned the eclipse trip, I never quite imagined it would come off. This fear was not helped by the fact that as soon as a 10-day weather forecast became available for the eclipse day at our planned viewing location of Lincoln, NE the weather services predicted "partly cloudy".

It was going to happen again, my heart told me. I now had kids the age I had been when we were clouded out in Hawaii, and I was going to take them to be clouded out in turn.

The morning of the eclipse itself did not reassure. The sun was in blue skies overhead, but the wind was from the south and clouds were blowing up from that direction. As the hours passed, the clouds closed in. They were, at least, high, thin clouds. As we looked up through our solar filters, we could see the sun, but we could also see wisps of cloud passing in front of it. Here's the view six minutes before totality:

We gathered under partly cloudy skies at the Lincoln Diocese's seminary.

As the remaining exposed part of the sun narrows to a sliver, the quality of the light changes. Like everyone, I'd heard all the warnings not to look at the sun without a filter, lest the image burn into my cornea. Yet, catching brief glimpses from the corner of my eye, I could see that rather than its usual brilliant disk the sun now had the quality of a very brilliant star. A star brighter than any in the real sky, bright enough to cast crisp shadows. But now very close to a point of light rather than a disk of fire.

The older kids were worried that baby would in his bleary way stare at the sun in this condition, so they put a hat over his head while he slept:

At last, it went dark. You could no longer see anything through a solar filter. And to confirm what we already realized, the leaders of our viewing group blew a whistle to let everyone know that for the next minute it was safe to look directly at the sun.

I lowered the filter I had been looking through and saw perhaps the most beautiful natural sight of my life.

I'd seen plenty of photographs of the total phase of a solar eclipse, the black disk of the moon surrounded by the ghostly white corona of the sun -- the sun's thin upper atmosphere which is normally invisible because it is so much dimmer than the sun itself.

Those photographs are beautiful, but they don't at all capture what you see with your eyes during a total solar eclipse. The human eye is an amazing thing, able to deal with differences of brightness and scale which a camera cannot. You've probably noticed this if you've ever tried to take a picture of a full moon rising over a landscape. To your eye, the moon looks huge, and you can see all sorts of detail on the moon itself while at the same time seeing the landscape in twilight. Yet if you try to take a picture, you'll notice several things: The moon looks much smaller if you have a wide enough field of view to see the full landscape. Also, you either see the landscape, with the moon burned-in as an undifferentiated bright blob, or else you see the moon clearly and the landscape is dark.

In camera terms, your eye has the ability to zoom in and out instantly, giving you a sense of the moon looking huge against the landscape features it's rising behind and also of the wider landscape. Your eye is also hugely adaptable to different levels of light, so it can both focus on the bright surface of the moon and make out details on it and also see the dimly lit landscape in the foreground. The only way to reproduce this in a photograph is to take two different photographs (one getting the moon clearly and one getting the landscape clearly) and combine them after the fact. And even then, a photograph can't reproduce the ability of your eye to see both narrow focus and wide angle at the same time.

So when the eclipse becomes total and you lower your solar filter to look at the sun with the naked eye, you don't see the totally black sky and the fringe of corona around the sun such as you see in up close photographs taken through telephoto lenses or telescopes. You see a dark but not black sky, with a few stars dimly visible, like the twilight sky half an hour after sunset. All around the horizon, however, you see the orange light of sunset, because in every direction you are seeing areas of sky not in the path of totality.

The sun (covered by the moon) is itself small. Just as at any other time, you could cover the sun with a thunbnail held out at arm's length. And yet the ghostly light of the corona seems to light up the sky around the black disk of the moon for a good eight or twelve solar diameters in every direction around the sun. And since your eyes can both zoom in on that sight of the sun itself, and also zoom out to look at the wider landscape, you perceive the sun and the halo around it as huge even while seeing the landscape, the horizon, and the sky all at once.

I tried to take a quick picture with my iPhone, but the sun is totally burned-in so that you can't even see that the moon is covering it, and really all it does is give you a sense of how perfectly the clouds parted to make it visible for us.

I've been searching like crazy for an photograph which gives even a slight sense of what seeing totality looks like. I found examples like this:


However, reading the description of the photograph I see that even this (which does not fully capture the effect) is in fact a "composite of simultaneous telephoto and wide angle frames".

Seeing a total solar eclipse is different from seeing a partial one (or a lunar eclipse) in kind, not in degree. Having finally experienced it, I want very much to do so again. The only thing that strikes me might be similar might be seeing the northern lights (something I have yet to experience.) However, even that is a strange effect during a normal night. This is something that sweeps down upon you in the middle of the day.

I can see now why some people travel the world to see eclipse after eclipse, and why they were taken as signs and portents in the ancient world. I can see why ancient peoples developed mathematics in order to calculate celestial events such as this. If you ever get the chance to see one, do not pass it up. It is one of the most wondrous things you will see.


Kathy said...

This is an excellent description of viewing the totality. Thank you for your explanation. I take personal credit for the parting of the clouds for the totality--I had asked God specifically for all of my family members to be able to see the totality. :-)

Joseph Moore said...

Nice write up, glad the clouds cooperated.

We made a huge family trip of it, getting all 4 of our now-scattered kids to come to Idaho and stay in a cabin together. I was worried it would be a disappointment for them - I'm the lone science geek in the family - but: spectacular. Awesome in the root sense. We were on the side of a mountain facing west across a huge valley, and so were able to see things go dark in stages a bit. I, being reckless and familiar with the modern tendency to overreact to risk, looked up just as totality was reached, and saw the string of pearls and diamond ring effects - again, awesome - both coming and going.

The kids were thrilled, and began spontaneously singing songs - spirituals and Bill Withers tunes (ain't no sunshine when she's gone, after all).

2024, here we come! The big question: Mazatlan? Never been. Texas or the Midwest? Easier, but still. Or Montreal or Prince Edward Island? There's an adventure!

Darwin said...

I'm glad it worked out for you too!

It really was an awe inspiring experience, much more so than I expected.

I only caught the diamond ring on the way out, but wow it was amazing.