Your ultimate guide to Monday’s Great American Eclipse
August 16, 2017
It's being called the Great American Eclipse. The BIG one. The one that astronomy enthusiasts in the USA have been waiting to see for 38 years. It's been a long eclipse drought.
On Monday August 21, the shadow of the moon will sweep across the 48 contiguous states, from coast to coast, putting millions of people within a short drive of one of nature's most breathtaking celestial events — a total eclipse of the sun.
Total eclipses of the sun are not rare. There's usually one somewhere on the Earth almost every year. The problem is that the area of visibility is exceedingly small — one-third of one percent of the Earth's surface — so you either have to be lucky enough that the eclipse happens close to where you live, or you have to travel a great distance to put yourself in the right spot.
It is one of nature's most marvelous coincidences that the sun is 400 times larger than the moon, but it is also 400 times farther from Earth. Consequently, the sun and moon appear to us to be the same size in our sky. But, because the orbits of Earth and moon are ellipses rather than perfect circles, there are slight variations in the apparent sizes of the sun and moon over the course of the month and year. Sometimes, the sun appears slightly larger than the moon, and sometimes, it appears slightly smaller than the moon. If the sun and moon cross paths at a time when the moon appears slightly larger than the sun, a miraculous total eclipse occurs. Under the very best of circumstances, the moon can cover the sun for only seven and a half minutes. Most of the time, it is much less than that.
If you were floating in the vacuum of space, all you would have to do to see a total eclipse of the sun is to hold your thumb up to cover it. You could then view the sun's corona and stars at the same time against the blackness of space.
The same trick does not work from the surface of Earth, because the atmosphere scatters the sunlight and creates a bright, blue sky. The sky itself is brighter than the faint corona and feeble starlight, so a thumb eclipse will not work. Only when the sunlight is blocked from above the atmosphere can the wonders of a total eclipse be observed. That's where the moon comes in handy.
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The most recent total eclipse of the sun visible from the 48 contiguous states was way back on Feb. 26, 1979. That one was visible only from the northwestern tier of states and across central Canada.
As a young man, I traveled from Young Harris, Georgia to Riverton, Manitoba, Canada to witness that eclipse. The sky was crystal clear and cold. The moon's shadow swept over me for 2 minutes and 49 seconds. The sun turned black, and its silvery corona flashed into view. The stars came out at midday. My heart was pounding, and my knees were wobbling as I shot frame after frame through my homemade, 6-inch telescope and the seconds ticked by. In 169 seconds, it was over, and daylight returned. It was a sweet success. Two years earlier, I had traveled to Columbia, South America for a total solar eclipse but was clouded out at the last minute. C'est la vie.
On Aug. 21, the moon's shadow will once again sweep across the USA, this time from sea to shining sea, casting parts of Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia and South Carolina into midday darkness. The shadow path is very narrow — only 70 miles wide — so, unless you happen to be living within that path, you get the "close but no cigar" award. From Craig, Colorado, the sun will be 94-percent eclipsed; from Steamboat Springs, 95-percent eclipsed. That's not enough to see all of the wonderful features of a 100-percent total eclipse.
I've chased, studied and photographed total solar eclipses from three continents over nearly five decades and spent a total of 31.4 minutes within the shadow of the moon. Total solar eclipses are hypnotic, if not addictive. They are much more than mere astronomical phenomena — they are awesome and emotional cosmic events that touch something primal in each of us. This alignment of worlds reveals mysteries of the cosmos that are normally hidden from the human senses. It is my experience that total solar eclipses connect me viscerally to the cosmic forces at work in the universe — and I like it.
A detailed map showing the path of the total eclipse across the USA can be found on the website greatameri
caneclipse.com. Assuming that you make the effort to plant yourself in that path of the moon's shadow, here is a description of some of the things you will want to watch for.
First Contact: The Partial Eclipse Begins
This is the term used to describe the moment that the dark disk of the Moon first takes a bite out of the edge of the Sun. Shouts of "First contact — there it is!" invariably rise up from the adrenalized crowd of eclipse watchers. For the next hour, the Moon covers up more and more of the bright face of the Sun during the partial phases of the eclipse.
As long as any part of the bright photosphere of the Sun is in view, it is unsafe to look at without a proper solar filter, so don't do it. Regular sunglasses are useless. Permanent eye damage can occur. The lens in your eye will focus that dazzling sunlight into a laser-like point on your retina and scorch it. Purchase a pair of CE and ISO certified safe solar eclipse glasses online for a couple of bucks. Then, you can watch the progress of the eclipse safely with your glasses on.
Maximum eclipse for northwestern Colorado happens between 11:40 a.m. and 11:45 a.m., local time. From Steamboat Springs and Craig, the eclipse will never be total, so you'll need to wear those eclipse glasses for the entire event.
One cool way to watch the partial phases of the eclipse indirectly is to place a sheet of white poster board underneath a leafy tree where the sunlight filters through. The overlapping leaves in the tree create hundreds of little pinholes that project shimmering images of the eclipsed sun all over the ground. This is one of my favorite ways to watch an eclipse.
Shadow Bands And the Approach of Totality
If you are within the path of totality, you get to see some very special things that are not visible from outside the path. In the fleeting moments just before and just after totality, sunlight from the vanishingly thin crescent of the Sun peeking around the edge of the Moon diffracts through the Earth's atmosphere and creates rapidly moving, flickering shadows across the ground.
I saw them best while watching the solar eclipse of June 30, 1973 from the deck of the MS Massalia, off of the west coast of Africa. While frantically shooting photos at my telescope, I became aware of flickering shadows moving across my arms. Looking down at the wooden deck, I watched the shadow bands racing at an angle across the deck planks. They remind me of the ripples of sunlight dancing on the bottom of a swimming pool. A white piece of poster board on the ground in full sunlight makes a perfect backdrop for viewing the shadow bands.
As totality approaches, amazing things begin to happen rapidly, so try to keep your wits about you. One of these is the appearance of Baily's Beads along the leading edge of the Moon, named for Francis Baily, who first explained this phenomenon in 1836.
The Moon is not a slick cue ball. On the contrary, there are towering mountains and deep crater valleys all along the edge of the Moon. In the last few seconds before totality, the crescent of sunlight will be broken into a string of beads, where high mountain peaks break the crescent and allow the last rays of sunlight to stream through the deep valleys. From the centerline of the total eclipse, Baily's Beads will be fleeting. The closer you are to the edge of the eclipse path, where the Moon just grazes the edge of the Sun, the longer Baily's Beads will remain in view.
The Diamond Ring
One by one, Baily's Beads will wink out as the Moon continues its march across the face of the Sun. When one final bead remains and darkness descends rapidly across the landscape, the last ray of sunlight creates a brilliant point of light, as if from a sparkling diamond. Pop off those eclipse glasses and watch one of nature's most breathtaking sights — the Diamond Ring effect. It is ever so delicate and fleeting and will last for only a split second. Try to be aware of the shouts of amazement and glee from those around you at the sight of the Diamond Ring. Chances are, you, too, will be unable to contain your amazement quietly and will join into the chorus of cheers and howls.
Second Contact: Totality and the Solar Corona
When the leading edge of the Moon reaches the opposite edge of the Sun, the Diamond Ring disappears, and totality begins with what is called second contact. It is now completely safe and appropriate to remove all eclipse glasses and filters and stare at the Sun. Believe me; you won't be able to stop yourself. Where once hung a glowing ball of life-giving light is now a jet-black orb, surrounded by an opalescent halo of fantastic arcs and streamers. This is the Sun's 10 million degree outer atmosphere called the corona. My experience is that the loud shouts and cheers of the eclipse watchers around you will turn, at this point, into wordless sounds of disbelief at the sight before them. The corona is always there, surrounding the Sun, but the blinding light of the photosphere renders it invisible to Earthlings — except during these precious moments of totality. Enjoy the view, because in mere seconds, the Sun will return.
During totality, you might notice one or more hot pink protrusions along the edge of the eclipsed Sun. These are solar prominences, Earth-sized flames of hot hydrogen gas leaping off of the Sun's photosphere. I have seen no other color in nature to compare with the fluorescent pink color of these prominences visible during a total eclipse of the Sun.
The most spectacular prominences I've ever seen came during the total eclipse of July 11, 1991. I had taken my two young sons, Jason and Michael, to Cabo San Lucas, Mexico to see their first total solar eclipse. During both the first and second Diamond Rings, there appeared gigantic prominences, one completely disconnected from the Sun and the other in the shape of a colossal seahorse, 10 times as tall as the Earth! Both were visible to the naked eye.
There is no guarantee that there will be any prominences visible at the time of the eclipse, but keep your eyes peeled for them, just the same.
Stars and Planets at Midday
It will be hard, ever so hard, to take your eyes off of that totally eclipsed Sun and the solar corona, but take a few of those priceless seconds to do so, because darkness will have fallen over the Earth at midday. This means that bright stars and planets will come into view.
Brightest of all will be the planet Venus, about two full hand spans at arm's length to the upper right of the eclipsed Sun, near the two o'clock position.
The sky's brightest star, Sirius, will be twinkling about four full hand spans to the lower right of the Sun, near the four o'clock position.
Look for planet Mars about one clenched fist at arm's length above the Sun at the one o'clock position.
Bright planet Jupiter will appear just above the eastern horizon, nearly four full hand spans to the lower left of the Sun at the seven o'clock position.
Most challenging of all will be the bright star, Regulus, Leo the Lion's brightest star. Regulus will be shining right through the solar corona only one degree, that's about two Moon diameters, from the edge of the Sun at about the eight o'clock position. I've never seen a star shining through the corona so close to the Sun, so I am particularly excited about this opportunity.
Animal Behavior and Other Stuff
Total eclipses are not just for the eyes. Open your ears and listen for sounds that are normally heard only at night — frogs and crickets chirping, mosquitoes humming, night birds singing and winging their way to their nests.
During the total eclipse of March 7, 1970, I was set up observing in the Okeefenokee Swamp Park in southeast Georgia, when night feeding alligators crawled up around me and my compadres, giving us quite a start. Animals and insects are confused by the sudden and unexpected onset of nightfall.
Also, watch for other dusk phenomena, such as streetlights coming on. During the total eclipse of July 10, 1972 from Prince Edward Island, Canada, a lighthouse right beside my observing spot flashed on unexpectedly. It might behoove you to make sure that your eclipse observing site is not under any streetlights — or lighthouses.
You will probably spy one or more high-flying airplanes, full of scientists and spectators, flying along and chasing the shadow of the Moon across the Earth. This will help extend the duration of totality for those passengers, but at the expense of being in a moving vehicle, making observations challenging.
Once you've taken a moment to observe the things going on around you, return your gaze to that heavenly sight of the corona for a final view. The total eclipse is almost over.
Third Contact: The End of Totality
Faster than you can sing George Harrison's song, "Here Comes the Sun," the 2 minutes and 20 seconds of totality for this eclipse will be over and the dark Moon will withdraw from the Sun. Daylight returns instantly at third contact. But, don't forget to watch for all of the same spectacular phenomena that accompanied the onset of totality, only in reverse: the Diamond Ring, Baily's Beads, and the shadow bands again.
At this point, put back on those safe solar eclipse glasses to watch the final partial phases of the eclipse. It ain't over 'till it's over — you have a whole hour of partial phases remaining before the eclipse ends at fourth contact. Chances are, the folks around you will start heading for their cars as soon as totality ends, but stick around and enjoy the final phases of the Great American Eclipse while reflecting on the spectacular things that you just experienced.
After watching this total solar eclipse, you might be hooked and want to see another one. The next total solar eclipse across the continental USA happens on April 8, 2024, less than seven years from now, but that one won't come as close to Nnorthwest Colorado. The Moon's shadow will cut a swath from Texas to Maine and treat folks living in the path to 4 minutes and 28 seconds of totality — nearly twice the duration of this month's eclipse.
This ain't horseshoes, folks. Close doesn't count. If you want to see the mysterious shadow bands, the eerie darkness with stars shining at midday, Baily's Beads and the Diamond Ring, the stunning solar corona and prominences, then do whatever it takes to put yourself in that path of totality! It's a short drive up to central Wyoming for the most stunning and breathtaking two and a half minutes you've ever experienced.
This is your big chance. Don't blow it.