Great American Eclipse: Everything you need to know about Monday’s event | AspenTimes.com

Great American Eclipse: Everything you need to know about Monday’s event

Jimmy Westlake
Special to The Aspen Times

It's being called the Great American Eclipse. The big one. The one that astronomy enthusiasts in the U.S. have been waiting to see for 38 years. It's been a long eclipse drought.

The shadow of the moon will sweep across the 48 contiguous states today, 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 Earth almost every year. The problem is the area of visibility is small — one-third of one percent of the Earth's surface.

It is one of nature's most marvelous coincidences that the sun is 400 times larger than the moon, but it also is 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. If the sun and moon cross paths at a time when the moon appears slightly larger than the sun, a total eclipse occurs. Under the 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.

The most recent total eclipse of the sun visible from the 48 contiguous states was Feb. 26, 1979. That one was visible only from the northwestern tier of states and across central Canada.

Today, the moon's shadow will once again sweep across the U.S., 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 Aspen, the sun will be 92 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.

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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.

Warning: 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; regular sunglasses are useless and 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.

Maximum eclipse for northwestern Colorado happens between 11:40 a.m. and 11:45 a.m., local time. For Aspen, 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.

Baily's Beads

As totality approaches, amazing things begin to happen rapidly. 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.

Stars and Planets at Midday

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.

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.

Also, watch for other dusk phenomena, such as streetlights coming on. It might behoove you to make sure that your eclipse observing site is not under any streetlights.

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.

Third Contact: The End of Totality

Faster than you can sing George Harrison's "Here Comes the Sun," the two minutes and 20 seconds of totality for the eclipse will be over and the dark moon will withdraw from the sun. Daylight returns instantly at third contact.

At this point, put back on those safe solar eclipse glasses to watch the final partial phases of the eclipse — you have a whole hour of partial phases remaining before the eclipse ends at fourth contact.

The next total solar eclipse across the continental USA happens April 8, 2024, but that one won't come as close to Northwest 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 is your big chance. Don't blow it.

Events in the valley

Here in Aspen, the sun will be 92 percent occluded at the peak of the eclipse; the eclipse will begin at 10:20 a.m., peak at 11:43 a.m., and end at 1:11 p.m. It will be celebrated in countless ways; here are a few local happenings:

IN ASPEN

Where: Galena Plaza, Pitkin County Library

When: 9:30 a.m. to 1 p.m.

Details: The Aspen Science Center, in partnership with the Pitkin County Library, will host eclipse viewing with telescopes, pinhole cameras, demonstrations and simulations about eclipses, games for the kids and more. More than 400 pairs of free solar glasses will be available, or you can make your own solar eclipse viewer.

More info: http://www.aspensciencecenter.org

IN BASALT

Where: Basalt Library

When: Monday, 10 a.m. to 2 p.m.

Details: The library’s telescope will be equipped with solar filters for viewing the eclipse and a limited number of free solar glasses also will be available. The event also will include free snacks and drinks, kids’ activites, and “noisemakers to scare away the dragon who ate the sun.”

More info: http://www.basaltlibrary.org