Basics of how a total solar eclipse occurs.
As the excitement builds to see the total solar eclipse today (refer to diagram at top) I am reminded of my own "near viewing" more than 50 years ago. (See totality path in graphic.) This was while I was completing my Astronomy degree at University of South Florida in Tampa, and the date was Saturday, March 7, 1970. Totality was to occur in Perry, Fl just over 200 miles distant and about a 4 1/2 hour drive. A group of 4 astronomy undergrads were planning to make the trip and wanted to know if I would join them. Alas, I had to pass as I needed to finish up an astronomy undergrad research project for Monday. As I later learned, the gr0up made the trip for nothing because overcast ruined it. According to the Wikipedia account:
Greatest eclipse occurred over Mexico at 11:38 am CST, with totality lasting 3 minutes and 27.65 seconds. Totality over the U.S. lasted up to 3 minutes and 10 seconds.[7] The media declared Perry as the first municipality in Florida to be in the eclipse direct path. Inclement weather obstructed the viewing from that location and most of the eclipse path through the remainder of the southern states.
So I didn't feel too bad I had avoided wasting over a day and maybe a weekend. But I felt bad for the ones who tried to see this once (or twice) in a lifetime event. As for the event today, I am just not prepared to make a bet again even though Texas and Arkansas are not that far away. But with family medical issues galore, it isn't possible to travel anyway.
What I will do is watch the spectacle unfold live on TV. A great option with no gouged-up motel rates, or traffic or crowed planes to fret over.
Bear in mind- as the eclipse diagram above indicates - the Moon's shadow is being projected not onto a flat surface, but onto a sphere (Earth). Near the middle of the totality path, the shadow is moving at its slowest along the surface of the planet. But at the very beginning of the totality path, and at the very end, the shadow is striking Earth at a very oblique angle at these points. Indeed, given the fact the lunar shadow cone is tangent to the curved surface of the Earth one can say it is moving at "infinite speed". (Why so many media pundits keep saying it will be "traveling faster than the speed of sound".)
What about those special eclipse-viewing glasses? Basically,
you will need them for all but the totality phase (assuming you can be in a location inside the
totality band). At that point (total eclipse) you can remove them because they become
useless. Besides, you'd miss one of the most spectacular sights, the
solar corona. Obviously, if you live outside the totality band area you
will need to wear your glasses for whatever duration you're viewing.
During the first hour of the eclipse phase (i.e. from
"first contact") few people would recognize anything unusual
happening. No surprise given that not much of the Sun is being covered. But pay
attention to the last 15 minutes or so before totality (again assuming you're
lucky enough to be in the totality band and have clear weather) and note the
sharpening shadows, changes in the light and sometimes cooling winds.
Without any doubt the most awesome period begins in the final
minute before totality, when the Sun transitions from being 99 percent obscured
to total coverage. By some estimates, the sky gets about 10,000 times
darker. It's absolutely eerie, as even assorted animals fall sway to the sudden
change in light intensity: bees return to their hives, spiders take in their
webs, birds cease their bird song etc.
Just before totality those lucky to be in the totality band (and escaping cloud cover) will
behold the interplay of sunlight and mountains in profile on the lunar
surface. These produce a phenomenon called "Bailey's beads.'
Note how the last bead gleams brilliantly just as the Sun's corona becomes
visible.
Ultimately, today's event is astronomical but one hopes the sociological and excitement aspect will allow millions to get away from politics and polarization at least for a day. To that end, I hope everyone will be able to enjoy this event to the max,
and maybe learn a bit about astronomy from it, even enticing further
exploration. For myself, I will have to be content with watching it from
televised accounts on the TV.
Addendum:
Colorado State University has an interactive satellite viewer that includes the eclipse track as an overlay for reference. The dark spot will increasingly show up on satellite imagery focused on the United States, as well.
See Also:
Eclipse Map - April 8, 2024 - NSO - National Solar Observatory
And:
Opinion: Science prepared us to witness the eclipse. Why do we feel estranged from it?
And:
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