Total eclipse a brief event of wonder, beauty

August 21 is E-Day across North America.

After years of anticipation, the “Great Solar Eclipse of 2017” finally stands on our doorstep.

And in this age of cellphones, this eclipse may become the most photographed celestial event in human history.

How can a 2,150-mile-wide moon cover an 864,000-mile-wide sun?

Though the sun is 400 times larger than the moon, it’s also 400 times farther away. That’s why these two celestial bodies appear equal in size as they cross the sky.

Because of this coincidence and the periodic alignment of the new moon, Earth and sun, the moon sometimes crosses in front of the sun.

If the moon covers all of the sun, it’s called a total solar eclipse.

Astronomers, plus millions of casual observers and ardent eclipse chasers, will be flocking to hopefully cloudless — and smokeless — observing sites in the moon’s 60- to 70-mile-wide shadow that runs southeast from the Pacific shores of Oregon to the Atlantic Ocean off of South Carolina.

A total eclipse is only visible to observers watching from inside the moon’s oval-shaped shadow (umbra) projected down upon the Earth.

In the Pacific Northwest, the moon’s shadow does not cross Washington state. This is why so many people are traveling south into Oregon.

Amazing, incredible, stunning, beautiful and even life changing are but a few of the adjectives eclipse viewers have used to describe their observing experiences.

After all, there is excitement and beauty in chasing the darkness of total eclipses across mountain ranges, valleys, oceans and deserts. Unforeseen sights stirred with unforgettable memories.

This month’s total eclipse is the first one visible across the contiguous United States in 38 years. Coincidentally, that eclipse passed directly across the Tri-Cities.

On average, any location on Earth will experience a total eclipse once every 360 years. This time, a thin ribbon of Oregon landscape captured the prize.

Partial eclipse

Except within the strip of land covered by the moon’s shadow as it races across 2,500 miles of the United States, all other land sandwiched between Canada and Central America will witness a partial eclipse.

Less of the sun is covered as you travel away from the umbra. For example, from north to south the maximum eclipse coverage in Eastern Washington is 91 percent for Spokane, 95 percent in Yakima, and 97 percent in Walla Walla.

On eclipse day in the Mid-Columbia, the sun will rise at 6:04 a.m. Three hours later at 9:09 a.m., the moon notches off a thin sliver of the sun’s upper edge. This marks what astronomers call First Contact — the beginning of the partial phase.

You can safely view first contact and the following 2 hours, 34 minutes of the partial eclipse if you use safe solar viewing filters.

By 10:23 a.m., the moon covers a maximum of 96 percent of the sun. The moon then slowly recedes from the sun. The partial eclipse ends at 11:44 a.m.

One of the misconceptions I’ve recently heard is that watching a partially eclipsed sun is just slightly less exciting than watching a total eclipse.

“After all, what difference does a few percent of sun coverage make.” This is like saying there is little difference between day and night or thunder and lightning. Totality ushers in a wholly different experience.

Nonetheless, if you are not traveling south to catch totality, watching the partial eclipse will be enjoyable and worth the time and effort — especially for young people watching their first eclipse.

The Moore Observatory at Columbia Basin College will be open eclipse day 9 a.m. to noon.

Safe viewing filters will be available in addition to close-up views of the eclipse using a variety of telescopes. You will want to arrive early.

Total eclipse

Few celestial events surpass the experience of a total eclipse. Those two short minutes likely will pass faster than any few minutes of your life.

Imagine standing near the eclipse’s center line.

Less than one minute before totality, glance toward the western horizon. If the sky is clear, you may see the moon’s shadow, stretched north to south, racing three times the speed of sound (2,200 mph) toward you.

The shadow will soon plunge your observing site into near darkness except for fringes of twilight. Some observers have been known to duck their heads as the shadow engulfs them. Totality has arrived.

The glowing lemon-tinted sun suddenly blackens into a dark cosmic eye that’s now surrounded by a rind of orange and loops of silver-white reaching outward from the eclipsed sun. Silence covers the landscape, temperatures drop, birds settle into their nests, and eerie bands of shadow race across the ground as breathless reverence fills your thoughts. You glance at your watch. The time has arrived.

The once excited voices of friends and family dampen into silence as the eclipse unfolds overhead and around you.

When totality arrives, eclipse filters are no longer needed. The once glowing sun blackens. Only the dim light of reddish solar prominences and the wispy corona extends from the darkened sun.

The total eclipse belies its ending as the sun’s lower left edge begins to brighten. The sun is returning. Sun filters should now be used for viewing any part of the remaining 1 hour, 20 minutes of the partial eclipse.

At its closest, this eclipse’s northern edge lies about 80 miles south of the Tri-Cities. The eclipse’s center line where totality lasts the longest is almost 115 miles south of the Tri-Cities.

A maximum of about two-plus minutes of totality will be visible across Oregon, starting between 10:16 a.m. and 10:25 a.m.

Along the umbra’s outer edge, only a few seconds of totality are visible. This time increases as the shadow’s center line is approached. Exact times and eclipse durations depend on where you are.

During an eclipse, three dominant regions of the sun can be seen. They are:

Photosphere: The sun’s surface where most visible light is released. Solar filters are required to safely view the surface. Any sunspots will appear as dark semi-circular blemishes on the photosphere.

Chromosphere: Marks the red rind of the sun’s lower-most atmosphere visible to the naked eye during totality. Resembles red tangled loops rising from and falling back into the sun.

Corona: Sun’s outer silvery atmosphere visible as an aura of intertwined loops, streamers, and plumes ascending outward for millions of miles along magnetic lines of force. Causes solar winds that create colorful auroras in the Earth’s atmosphere.

The beginning and end of the total eclipse are easy to anticipate. This is especially important when supervising children watching the eclipse.

Take time to photograph the eclipse but don’t forget to glance around to secure that moment in your memory.

This story was originally published August 13, 2017 at 2:43 PM with the headline "Total eclipse a brief event of wonder, beauty."