Monday, August 14, 2017

Another Eclipse Post. . .

As we draw closer to The Great American Eclipse of 2017, a few thoughts are percolating in my brain (which is not quite as painful as it sounds). . .

Of course, a solar eclipse happens when the moon passes between the earth and the sun, and what's so complicated about that?  But when I think about it. . . It is at least a colossal conincidence (or is it?) that the moon and the sun are almost exactly the same size, when viewed from here on earth.  The moon is about a quarter the diameter of the earth, and the sun is about 100 times bigger than Earth.  But the sun is about 400 times farther from the earth than the moon, so they look to be about the same apparent size.  If the moon were a little bit smaller, or a little farther from earth, it would never be able to cover the sun (and all eclipses would be like the one in '94 that passed near OurTown).

Eclipses always correspond with a New Moon - when the moon passes from one side of the sun (viewed from our persepctive here on earth) to the other.  In fact, if the moon's orbit were coplanar with the earth's (i.e. perfectly 'flat' to earth's orbit), every new moon would result in an eclipse.  But because the moon's orbit is tilted by 6 degrees relative to the earth's, the moon sometimes passes above the sun, sometimes below it.  If the earth were bigger (I don't really know how much bigger would be 'big enough'), then the likelihood of the moon's shadow crossing the earth would increase, and there would be more eclipses.  As it is, total eclipses occur roughly every 1-2 years, somwhere on the planet (and the fact that it's been almost 100 years for the US means we're WAY overdue) (but, to make up for it, the next one comes less than seven years from now, in April 2024). . .

So, an eclipse happens when a new moon corresponds to the moon being at a point where its orbit is crossing the earth's orbit (or at least, 'close enough' to it).  And where the eclipse falls on the surface of the earth just depends on which part of the earth is turned toward the sun at the moment.  Next week just happens to be when our turn comes up here in the good ol' USA, for the first time in virtually a century.

It blows my mind a little bit that things like eclipses are mathematically predictable, to a high degree of precision.  I mean, we know when the eclipse is going to happen and where it's going to happen.  There are published maps, showing the path of totality, and how wide it is, and which towns are in the path of totality, and which are just outside it.  If you're on the southwest side of St. Louis, you'll see the totality; if you're on the northeast side, you'll just miss it, and we know that before it even happens.  We know how the eclipse will progress across the country, starting in Oregon around 10:15 AM Pacific Time, and ending in South Carolina about an hour-and-a-half later, mid-afternoon Eastern Time.  We know that the totality will last for just longer than two minutes (two minutes and 40+ seconds in Missouri/Illinois/Kentucky, where Jenn and I will (hopefully) be).  I mean, that's knowing an awful lot about how it's all going to happen, and it was known years, even decades ago. . .

Jenn and I are laying our plans to drive down next Sunday afternoon/evening.  We'll actually be staying with an old blogger-friend who lives not too far from the path of totality (but not actually inside it), then getting up early on Monday to fight the (hopefully not TOO awful) traffic, and settle in a decently favorable location from which to track the progress.  The long-range forecast, at least as of today, is pretty favorable for good viewing.  Hopefully, it will stay that way.  Then, sometime around 1:30 or so, the lights will go out.  And that's what I'm waiting to see. . .

-------------------------

And of course, there are those who are just unclear on the concept. . .

In the meantime, I'm trying not to get too irritated with Jenn singing that old Bonnie Tyler song, over and over and over and over. . .

Monday, August 7, 2017

Signs In the Sky

By now, most of you, or at least some of you (okay, the nerds among you) have heard about the total solar eclipse that is due to happen on August 21, two weeks from today.  This is the first total eclipse visible in the continental United States since June of 1918, nearly a century ago.  So it's a pretty big deal, as eclipses go.  Over a narrow band maybe 50 miles wide, stretching from the Oregon coast to South Carolina, the moon will blot out the sun, for as much as two-and-a-half minutes, stretched over a couple hours, from coast to coast.

Jenn and I are planning to drive down to Hopkinsville, KY (about 8-9 hours drive time from OurTown), braving what will probably be pretty brutal traffic, at least by Hopkinsville standards.  Depending on what we see in the weather reports the day before, we could end up anywhere from Illinois to Tennessee, or just stay home, if we see that the eclipse path will be clouded under.  But we are looking forward hopefully to a once-in-a-lifetime opportunity to see the sun blotted out in mid-day.  I'll certainly blog about it, once we get back. . .

But until then, I'll whet your appetite with a few reminiscences of heavenly phenomena I've been witness to in the course of my young life. . .

-------------------------

The earliest solar eclipse I can remember happened in July of 1963, when I was seven years old.  Our family was vacationing at a beach resort near what would soon become our hometown UpNorth.  In retrospect, my dad was probably interviewing for the job that would have us moving there the following November (just after the Kennedy assassination), and his bosses wanted to impress upon him the pleasantness of life on the Big Lake, in the midst of the North Woods.

Anyway, seven-year-old me was mostly happy to splash around in the Big Lake, among the sandbars and whitecaps; I recall it being sunny and warm for our entire stay there.  Then one day, folks gathered on the beach, with an air of excitement, talking about 'the Eclipse'.  Precocious (read: nerdy) child that I was, I had read age-appropriate astronomy books (maybe even a year or two above my grade-level), and knew what an eclipse was (at least in theory), but I had never seen one live and in-person.  My dad was a pretty mechanically-clever guy, and he rigged up an eclipse-viewing box, with a pinhole on one end, and a 'screen' of white cardboard on the opposite end (which, honestly, didn't require that much mechanical cleverness, but still. . .), so we could watch as the 'bite' the moon was taking out of the sun grew.  At that location, the eclipse reached a maximum of something like 85% totality.

There was much dire hand-wringing among the adults that we MUST NOT look directly at the sun, lest we go blind, so dad's little box-viewer was what we had available.  But, naughty boy that I was, I snuck off for a minute or two. I had, from time to time in my young life, squinted with my eyes just barely slitted open, and looked straight at the sun for a couple seconds, so I had reason to doubt the whole 'going blind' thing.  I wondered briefly if there were some sort of special rays or something associated with the eclipse, but decided that I'd done it before, and if I did it again just now, it probably wouldn't be any different.  So I did - just enough to confirm for myself that, viewed directly, through my tightly-slitted eyelids, the sun looked pretty much the same as what we saw in dad's box, so I was mainly content to view the eclipse via the box, for the rest of the duration of the eclipse, although I probably risked a couple more quick views through slitted eyelids.  I think one of the men at the resort had a welding hood with him, which was quite popular with the other vacationers present. . .

Anyway, it was very cool.  As the eclipse approached its maximum totality, the light had a strange, ethereal dimness about it - sort of twilight-ish, except that the sun was high in the sky, and shadows were mid-day short.  Very cool. . .

The event probably stayed in my brain because of the vacation aspect of it, combined with (especially) my mother's anxiety over my impending blindness.  Or, you know, maybe I'm just a nerd. . .

-------------------------

In the course of 50-plus years since that first eclipse, I've experienced several other solar eclipses; this will be the sixth one in my lifetime to be more than 70% here in Michigan.  Some of them I've taken notice of, some of them came and went without me noticing much.  But there was another one, in May of '94, that is worth telling a story about. . .

The eclipse of '94 was an annular eclipse, meaning that the moon's disk was slightly smaller than the sun's disk (i.e., the moon was at a farther point in its orbit), so it wouldn't completely cover the sun.  But the path of maximum eclipse passed very close to OurTown, so the local news was in more-than-normal 'hype mode' for it.  One of the articles mentioned that a Number 14 welding shade was sufficient to allow viewing of the sun.  So I went to a local welding-supply store, and asked for a Number 14 shade.  "Number 14?" the guy said, when I asked him.  "Jeez, what are you trying to do?  Look at the sun?"  Well, yeah, I said.  "Well, I don't have a Number 14," the guy continued, "but if you slap a Number 6 and a Number 8 together, that's a 14; that ought to work.  I asked if he had a 6 and an 8 handy, so I could check it out.  He handed them to me, and I went out to the parking lot, put the 6 and the 8 together, and looked through them up at the sun, and saw the clear, green-tinted disk of the sun, at a comfortably dim brightness, comparable to the night-lights in my kids' bedrooms.  So the man had himself a sale. . .

A group of 5 or 6 of us played hooky from work for a couple hours on the day of the eclipse and drove to the county fairgrounds, maybe 15 miles from our office, and watched the familiar progression of the moon taking an ever-larger bite out of the sun, while the light took on the other-worldly dimness that I'd been through a few times by then.  At its peak, the sun was 96% blocked out, so the dimness was even more ethereal than usual that day.  My Number 14 welding shade was quite popular with my fellow-truants.

Our location at the fairgrounds was in what was called the 'Graze Zone', where the edge of the lunar disk just 'grazed' the edge of the solar disk, producing a very cool effect. At the height of the eclipse, the sun 'peeked through' the valleys between the lunar mountains, producing a 'string of pearls' effect, with a series of tiny pinpoints of light arrayed in an arc between the 'horns' of the thin crescent of the sun that remained visible.  And we saw it live, mitigated only by the green welding shade. . .


-------------------------

Up to now, that 'string of pearls' is probably the coolest thing I've ever seen in the sky, although a few other things deserve at least a mention. . .

Halley's Comet came by in 1986, right on schedule, with all the hype that you would expect for a well-known once-in-a-lifetime event.  We have friends who have a farm 30 miles or so from OurTown (away from city lights), so we arranged a Halley's Comet viewing party with them, and the kids we both had at the time.  We actually stayed overnight at their house, and got up at 5AM, to catch the viewing window between when Halley would rise over the eastern horizon, and when the dawn's early light would wash it out.  It was pretty deep in winter at the time, so we ended up trudging across their barnyard in the snow (at 5AM), with temperatures hovering around 10 degrees or so (Fahrenheit; about -12C).

And Halley was pretty much of a dud.  We consulted our star charts, to be sure that we were looking in the right part of the sky, pointed our binoculars at the correct sector of the sky, and saw. . . a little smudge of light that wasn't on the chart.  That's all - just a little smudge.  We had to look several times to convince ourselves that it wasn't just a snowflake on the binoculars.  Once we had convinced ourselves that, by golly, that little smudge was Halley's Comet, we sighed, declared victory, and trudged back to the house to go back to bed.  While our kids wondered what the hell we had hauled them out into the frozen night for. . .

But in 1997, Hale-Bopp was a comet actually worth watching.  I think it took even the astronomer-types by surprise by how bright and prominent it was.  For weeks, there was this large, sort-of V-shaped apparition in the evening sky, visible even walking amid the bright lights of OurTown.  Nothing ambiguous or smudge-y about this one.  Very cool - the best comet I've seen in my young life. . .

In 2012, there was a Transit of Venus, in which Venus passed across the disk of the sun.  It happened rather late in the day here in Michigan, so I took my Number 14 shade to work with me, and at a suitably remote location on my drive home, I pulled off the highway and took a look at the sun.  And sure enough, there was a small black dot in the middle of the sun's disk - Venus, doing its very best to block out the sun (which amounted to something on the order of a 0.1% eclipse).  Not nearly as spectacular as even a partial eclipse, but very cool, nevertheless. . .

(There was also a transit of Mercury just last year, but it happened at an inconvenient time (early in the morning), so I missed it.  Plus, Mercury is both smaller than Venus, and farther from Earth, so it's harder to see.  But I wanted you all to know that I knew about it. . .)

-------------------------

There are others, I'm sure (I recall a pretty cool triple conjunction involving Mars, Jupiter and the moon, I think), but those are the major highlights of my sky-viewing experience so far.  At least until August 21, I hope. . .