Dyer-2006 Libya - Composite

Eclipse 2017: Waiting for the Big One

Put yourself in the path of the Moon’s shadow for this year’s most exciting astronomical show.

August 21, 2017, brings the first total solar eclipse to the continental United States since 1979, opening the door for two generations of eclipse-starved Canadians and Americans to see the Moon pass in front of the Sun without having to board an airplane or a ship. If you live anywhere within a 100- to 115-kilometre-wide strip stretching from Oregon to South Carolina, the eclipse comes to you. For the rest of us, viewing the spectacle requires a bit of travel.

Dyer-2006 Libya - Composite
Eclipse spectacle: The fabulous sight of the diamond ring effect (left and right) and the corona of the Sun surrounding the disc of the Moon (centre) awaits those who travel to the path of totality in August 2017. These views were captured from Libya in March 2006. (Composite photo by Alan Dyer)

The Circumstances

Solar eclipses occur at regular intervals as Earth and the Moon go about their cyclical journey around the Sun. August’s event is of a relatively modest duration, but it’s the first eclipse to cross the entire width of the United States since 1918. Interest has been steadily growing for the past few years, and by the time the big day arrives, excitement will be at a fever pitch.

To see a total solar eclipse, you have to be in the path of the Moon’s shadow as it races across the Earth’s surface. If you’re a bit outside of this narrow zone, you witness only part of the solar disc being covered. And though that’s an interesting sight, a partial eclipse is a little like listening to the roar of the crowd from outside the stadium while a bases-loaded home run is scored inside.

Eclipse Track
Eclipse track: For the first time since 1918, the Moon’s shadow traces a path from coast to coast across the United States. This is also the first eclipse since 1979 that you can easily drive to from Canada. Choosing the ideal viewing location depends on where you live, the location of the eclipse track and the prospects for clear weather on eclipse day. (Jay Anderson)

The Moon’s shadow first touches down at sunrise in the North Pacific, about 2,400 kilometres north of Honolulu, Hawaii. Nine minutes later, it reaches the Oregon coast and begins a 4,000-kilometre, 1-hour-and-31-minute cross-country journey to South Carolina. The middle of the eclipse path—where the centres of the Sun, Moon and Earth appear in exact alignment—is in Kentucky, but the greatest duration (2 minutes 40.2 seconds) takes place slightly farther west, in Illinois. To find the specific circumstances for any location along the eclipse path, visit Xavier Jubier’s excellent web site.

But with such a huge range of locations available, where should you go for the best view? Two main factors come into play when choosing the ultimate observing spot: the location of the eclipse track and the weather prospects for the big day. While the path of the Moon’s shadow is entirely predictable, the weather, sadly, is not.

The following aphorism was popularized by science fiction writer Robert Heinlein: “Climate is what you expect; weather is what you get.” Long-range averages are great for advance planning, but savvy eclipse chasers are always ready to move if the forecast for the big day looks bad. As August 21 draws nearer, I will post detailed weather and climate information on my web site.

Cloud cover maps
August weather: This pair of maps shows the eclipse path and the average cloud cover for the month of August, neatly summarizing the climate situation. As illustrated by the scale, blue indicates few clouds, orange and red more. (Jay Anderson)

Oregon and Idaho

While coastal Oregon communities, such as Lincoln City and Newport, are tempting, they’re on the wrong side of the mountains and are fully exposed to moist Pacific air. Salem, on the other hand, lies in the Willamette Valley south of Portland and is protected from ocean winds by the Coast Range. Sites in the Willamette Valley benefit by a 10 to 20 percent reduction in average cloud cover compared with coastal venues. Madras, furthermore, is tucked in the Columbia Basin, behind the much higher Cascade Range, where the climate is distinctly drier. Indeed, this is one of the sunniest locations along the entire eclipse track.

In southern Idaho the eclipse is about eight seconds longer and the Sun is higher in the sky than farther west. Climatology data show that this location is virtually tied with the Oregon sites when it comes to the frequency of sunny skies in August. Idaho Falls is another good spot but has a slightly greater (5 percent) amount of average cloud.

Wyoming and Nebraska

Sites along the eclipse path in Wyoming have to be chosen carefully to avoid clouds that build over the mountains during the day. Fortunately, the eclipse occurs in the morning, when these convective clouds are small. Any convective cloud should dissipate as the approaching Moon shadow brings cooler temperatures. At Casper, the aver­age cloud cover ranges between 30 and 40 percent—measurements show that August garners about 75 percent of the maximum sunshine possible. Those are pretty good numbers.

The big advantage to sites in Wyoming and Nebraska is that they offer the option to relocate at the last moment should the weather take a turn for the worse. Interstate highways run east and west through the two states, allowing an eclipse chaser to drive hundreds of kilometres while remaining largely within the eclipse track.

East of the Mississippi

As the path of the lunar shadow approaches and passes the Missouri and Mississippi Rivers, increasing cloudiness becomes a problem. The average cloud cover in Missouri and Illinois is about 25 percent higher than the best spots in the western mountains, though sunshine amounts are only about 15 percent lower, at around 65 percent. However, from these locations, the eclipse occurs in the early afternoon, when convective clouds are likely to build, especially as the track heads east from the Mississippi River into Kentucky and Tennessee.

Since cloud cover increases the farther east you travel, Carbondale, Illinois, is probably the best destination for eclipse chasers from Ontario and Quebec. Carbondale also happens to be the destination with the greatest cachet. It’s situated very close to Giant City State Park, where the eclipse has its greatest duration, and it’s also at the intersection of two eclipse paths—2017 and 2024—giving Carbondale bragging rights as America’s Eclipse City. If you head to Illinois, however, keep an eye on the forecasts and be prepared to divert, most likely to Kansas or Nebraska.

The best sites in South Carolina are on the coast, which has about the same cloud-cover statistics as Carbondale, thanks largely to the cool waters of the Atlantic Ocean, which suppress afternoon convection. Inland regions of the Carolinas and Georgia have much higher afternoon cloud amounts, due to the effects of the Appalachian Mountains and a humid subtropical climate. The same is true in Kentucky and Tennessee.

Get Ready to Get Ready

Indonesia eclipse
The beauty of totality: One of the most spectacular eclipse phenomena, just moments before totality, is the appearance of Baily’s beads—fragments of sunlight shining through valleys on the limb of the Moon. Bright, electric red prominences projecting from the solar disc are also an eclipse highlight. (Judy Anderson)

Finally, no matter where you plan to view the eclipse, your accommodation options are now pretty limited. Along much of the western part of the eclipse track, hotels, motels, and camp sites have been fully booked for months. The only large city west of the Mississippi with substantial accommodations is Casper, Wyoming. East of the Mississippi, you can choose from hotels available in Kansas City or St. Louis, Missouri; Nashville, Tennessee; and Charleston, South Carolina.

The 2017 eclipse comes at a time of year when weather prospects are generally good and many people are on vacation. So give yourself a late-summer holiday and take the family. It’s something they will remember for the rest of their lives.

Jay Anderson is a meteorologist, formerly with the Meteorological Service of Environment Canada, and a dedicated eclipse chaser, having witnessed totality 30 times.

Important safety note: When viewing the partial phase of a solar eclipse, or the Sun directly at any time, it’s vital that you use an appropriate solar filter. Observers using binoculars or telescopes should use a front-aperture solar filter. Those viewing the Sun without optical aid should use an eclipse viewer.