Ready for the Great American Eclipse? We present The 2017 Total Solar Eclipse Guide by Almanac astronomer Bob Berman, courtesy of The 2017 Old Farmer’s Almanac. This August 21 eclipse—the first to appear over the mainland United States in nearly 40 years—will be a historic event, with or without the media hype. Bob tells you everything you need to know.
First, What Exactly Is a Solar Eclipse?
To the naked eye, the sky is an inverted bowl hosting thousands of glowing points and two disks. The points—stars and planets—exhibit no size because of their immense distance from Earth. The two disks are the Sun and Moon. By amazing coincidence, these disks appear exactly the same size. Why?
The Sun is 400 times larger than the Moon but also 400 times farther from Earth than the Moon. These facts allow the Moon to fit perfectly over the Sun’s face to create a total eclipse. Yet, it’s not so big that it blocks out the Sun’s dramatic hot-pink corona or atmosphere and not so small that it leaves the Sun’s blinding gas surface (photosphere) uncovered. This bizarre alignment does not hold for any other planet and will not last forever: The Moon is spiraling away from Earth like a skyrocket and gradually increasing its separation.
Eclipses have piqued observers’ interest for centuries. Here, a print from 1871. Photo by Wellcome Images/Wikimedia Commons.
The perfect lineup of these two disks (Sun and Moon) to form a total solar eclipse does not happen often—just once every 360 years, on average, for any one point on Earth. (This is one reason why relatively few people have ever seen one.) The U.S. mainland is currently experiencing its longest totality drought in history. The last total solar eclipse occurred on February 26, 1979, over northwestern states and south central Canada.
This cycle of paucity finally ends with this year’s total solar eclipse, taking place on August 21, 2017.
What Happens During a Total Solar Eclipse?
For sheer visceral impact, a total solar eclipse is not even remotely comparable to a lunar eclipse, a partial solar eclipse, or even major auroral displays. A solar totality stands alone. If you are in the right place, it creates darkness in daytime along a 140-mile-wide ribbon of Earth. The brightest stars come out in midday but not as you might presume: During totality, they appear in seasonal reverse. In summer, the winter constellations emerge; during a winter solar totality, summer’s stars appear.
And that’s not all.
An uncommon mind-set takes over people when the Sun, Moon, and your spot on Earth form a perfectly straight line in space. Many observers shout and babble. Some weep. Afterward, everyone proclaims it to be the greatest spectacle they have ever beheld. Beyond that, many are speechless. (Animals also exhibit odd behavior, such as falling strangely silent.)
The experience surpasses all expectations and imaginings:
- The eye sees the transition of the Moon over the Sun differently from photographs; because of under- or overexposure, a camera lens can not capture the same range of brightness as human vision.
- The delicate tendrils of the Sun’s corona splay into the surrounding sky in a manner wholly different from the way they appear in photos.
- During the 10 minutes before and after totality, when the Sun is more than 80 percent eclipsed and its light arrives only from its edge, or limb, earthly colors turn richer and more saturated, while shadows become stark and oddly crisp—as if a different type of star is illuminating Earth.
- As the Moon slides over the Sun, not only is light blocked in the ribbon of space, but solar heat is, too. The steady drop in temperature usually results in a haunting eclipse wind.
- At 1 minute before and after totality, all white and light-color ground surfaces underfoot (sidewalks, sand, the like) suddenly exhibit shimmering shadow bands everywhere. (Think of black lines on the bottom of a swimming pool that appear to wiggle.) This eerie phenomenon can make your hair stand on end, yet it can not be captured on film. (Try it!) Recent research suggests that shadow bands are the edges of atmospheric temperature cells (air pockets) made visible by the remaining tiny point of Sun. Their motion catches the eye despite their extremely low contrast.
To witness these extraordinary phenomena, you need to be in totality’s path (see map, below). This year, you can drive into it and watch from a roadside! Totality lasts longest—over 2 minutes—within the centerline of the ribbon. A partial eclipse will be visible outside of that ribbon, but the phenomena described above will not occur there.
The Solar Eclipse’s Path
To see if your town falls within the 2017 eclipse’s path, check out NASA’s Interactive Total Solar Eclipse Map, as well as the simplified version, below.
- The eclipse’s path starts over the Pacific Ocean and first touches land in Oregon.
- The Moon’s shadow then traverses southern portions of Idaho; passes directly over both Jackson and Casper, Wyoming; and continues eastward over Nebraska in late morning.
- The path continues east and south, eventually passing over St. Joseph, Missouri, before continuing on to Carbondale, Illinois, where it reaches its maximum duration of totality and where the Sun will be highest in the sky. (Each location has a different clock time for totality. It happens during the morning over the Pacific Northwest, midday over southern Illinois, and afternoon over the southeastern states.)
- The eclipse shadow continues east and south in the mid-afternoon and concludes its track over Nashville, Tennessee; Columbia, South Carolina; and a lot of smaller communities.
On the day of the eclipse, NASA will be holding a number of eclipse-themed events across the country. Click here for a map of official events and viewing locations.
If possible, travel to where the forecast predicts clear weather.
For viewers outside of the ribbon of darkness (virtually the entire continent), this will be a partial eclipse, a fairly frequent sight (which does require eye protection) that is interesting, yes—but nothing like solar totality.
The cost to watch this wondrous event is affordable for most people. For about $5 to $10, purchase “eclipse glasses” online or buy welding goggles at the nearest welding supply store. Choose shade number 12 or 14 filters. Number 12 makes the solar image a bit brighter, but since the Sun will be high for this eclipse, 14 is probably ideal—but either will work. Do not use any other number.
Use the filtered shades during the hourlong partial phase before totality and then again afterward for an hour. Once totality begins, you can watch the event for the duration of totality (between 2 and 2-1⁄2 minutes) with naked eyes or through binoculars. The moment the first speck of sunlight returns at the edge of the Moon, look away and use the filter again.
When is the Next Total Solar Eclipse?
Total solar eclipses can be addictive. Fortunately, fanatics—and anyone who misses this year’s event—won’t need to wait 38 more years for the next U.S. and Canadian one—only 7. On April 8, 2024, solar totality will unfold over the continent in a path that curves north from Texas; passes over Cleveland, Ohio, and Buffalo and Rochester, New York; sweeps over Burlington, Vermont; and then continues across central Maine and eastern Canada.
But why wait? Circle August 21, 2017, on your calendar and plan a rendezvous with the Moon’s shadow this summer!
See our Eclipse Dates page to find out when other upcoming eclipses will occur.
More! The Great American Almanac is “Great American Eclipse Central”
Yes, The Old Farmer’s Almanac—your calendar of the heavens—has even more eclipse information for all you sky lovers!
Lots of folklore …
A little history …
Looking forward …
Watching the weather …
Where to go on the path of totality …
- Planning for The Total Solar Eclipse
- How Often Do Total Eclipses Occur? Are They Really Rare?
- 7 of the Best Places to See the 2017 Total Solar Eclipse
What if you’re NOT in the path …
Staying safe …