The "Great American (Total Solar) Eclipse" of August 21st, 2017Frequently Asked Questions
Notice: This page contains information on how to safely view a solar eclipse. Due to unforeseen accidents or improper use of filters, looking at the sun, even
with proper safety equipment, may increase the possibility of eye damage, so do it at your own risk! The information below is intended to decrease the
likelihood of being injured, but there's no such thing as a 100% guarantee—please exercise caution.
General Eclipse Info
Q1: What happens during a total solar eclipse?
A1: While a partial solar eclipse is fascinating and worth seeing, a total
solar eclipse offers everything a partial does, plus much more. Many who have experienced
totality describe it as an incomparably beautiful and awe-inspiring event. For viewers along the eclipse center line, the partial phases preceding and following
totality must be viewed with solar filters, just like locations far from the shadow path.
In the moments before totality:
- Alternating light and dark rippling "shadow bands" (caused by sunlight, reduced to a near-"point source,"
refracting through regions of varying air density in Earth's atmosphere) will appear on flat, uniformly-colored surfaces near the ground.
- Sunlight passing through pinholes (e.g. spaces between leaves in a tree) will produce tiny, narrowing crescents on the ground.
- Just before the sun is completely covered, it becomes safe to view without filters as tiny glimmers of sunlight shine through low topography (valleys or canyons)
on the moon's limb, creating the appearance of bright dots of light around the dark sun ("Baily's Beads").
- The sun's outer atmosphere (the solar corona) becomes visible as a pearly ring of streamers radiating outward.
The final Baily's Bead plus the corona produces a brief "diamond ring" effect.
|The total solar eclipse of July 22nd, 2009. In addition to the "diamond ring" produced by the last bright glint of sunlight (the "diamond") and
the ghostly solar corona (the "ring"), note the tiny red prominence visible just below the "diamond." (Photo by David Cornfield, MIT.)
- Once the sun is completely eclipsed, reddish gas eruptions ("solar prominences") may become visible around the dark moon.
- The corona becomes easier to see. (Note: The 2017 eclipse occurs about half-way between the last (relatively weak) solar maximum in mid-2013 and the
upcoming solar minimum in the early 2020s, so the corona may not be particularly prominent for this eclipse.)
- The sky darkens dramatically, with bright stars and planets becoming visible at mid-day. Mercury, Mars, and Venus should be visible near the obscured sun
during the 2017 eclipse; Leo's brightest star, Regulus, will lie just one degree from the moon's limb; and Jupiter will sit low on the eastern horizon for viewers in
the Western U.S.
- Birds begin chirping or seeking their roosting spots and cows start heading for their barns, as though the day had ended and nightfall was imminent.
All the pre-totality events repeat, in reverse order: The diamond ring, Baily's beads, and shadow bands reappear, followed by partial phases (requiring filters).
None of the phenomena described above are visible unless you are in the path of totality.
All in all, a total solar eclipse is a truly unique, dramatic, and
unforgettable experience, so much so that after seeing their first total solar eclipse, some "umbraphiles" ("shadow lovers") will go to great lengths to see as many total
eclipses as possible.
Q2: I saw a solar eclipse a few years ago—what’s the big deal?
A2: Many people have a recollection of seeing a total solar eclipse, but most likely what they saw were only partial phases when a total solar eclipse was happening
elsewhere. If you saw the eclipse from your home or school (i.e. you didn’t take travel specifically to see it), it is exceedingly unlikely (although not impossible)
that you just happened
to be in the narrow path of totality. For a description of the dramatic differences between partial phases and totality, see
"What happens during a total solar eclipse?"
Q3: How can I photograph the eclipse?
A3: The sun will appear quite small in photographs unless the camera has a powerful (zoom) lens. Photographing the partial phases without a filter could damage the
camera (and your eye, in the case of a camera with a through-the-lens (single lens reflex) viewfinder), since the lens will concentrate the sun’s energy onto the shutter,
detector, and/or viewfinder. During totality, it is safe to photograph the eclipsed sun without filters, but care must be taken to point the camera away before the
first glint of sunlight begins peeking out from behind the moon (the second "diamond ring"). Also, the rapidly-changing light levels can make eclipse photography
particularly challenging. All that being said, if you want to try your hand at eclipse photography, Fred "Mr. Eclipse" Espenak has an excellent
with lots of helpful suggestions.
Particulars of this Eclipse
Q4: Where is the best place to view this eclipse?
|The path of totality of the August 21st, 2017 eclipse (by Fred Espenak, NASA's GSFC).
A4: For approximately 90 minutes, the moon's shadow will sweep eastward across the U.S., from its first land contact in northwestern Oregon, to its last in southeastern
South Carolina. Viewers in southern Illinois will experience the maximum duration of totality along the shadow path, with the sun completely obscured by the moon for
2 minutes, 40 seconds. However, weather prospects (based on historical data for the frequency of overcast skies in late August) indicate that the best chance of clear
skies along the eclipse path are to be found in the Western U.S., specifically north-central Oregon (average cloud cover 34%), eastern Oregon (average cloud cover 35%-40%),
eastern Idaho (average cloud cover 37%-43%), and central Wyoming (34%-50%). Although the duration of totality will be somewhat shorter in the West, most experienced
eclipse chasers will be opting for higher probabilities of clear skies over the "all or nothing" gamble of going to a site more likely to be clouded out in the hope of
getting a few more seconds of totality. Be aware that overnight accommodations along the entire path of totality have largely filled up as of late 2016.
Q5: How can I determine exactly where the shadow path will be?
A5: NASA has an excellent web site
with an interactive
map showing the path of totality
Eclipse Circumstances for Idaho and the Magic Valley
Q6: What will people see in the vicinity of Twin Falls, ID?
|Simulated view of the sun at maximum eclipse (August 21st, 2017, 11:30 AM MDT) in Twin Falls, as seen through a solar telescope (by Chris
Anderson, using Software Bisque's "TheSky6").
A6: The path of totality (the moon’s full shadow) does not pass through Twin Falls, so it will only be a partial eclipse here, lasting from 10:12 AM to 12:54 PM MDT. At
maximum eclipse (11:30 AM), the moon will cover 97% of the sun's disk, leaving only a very thin, intensely bright "sliver" of the sun's surface exposed. The level of
illumination on the ground will be noticeably dimmer than normal. The sky will look a little darker than normal. Since the sun will not be completely eclipsed,
proper solar filters are required to look directly at the sun safely from Twin Falls throughout the entire eclipse.
Q7: How long will the eclipse last in the vicinity of Twin Falls, ID?
A7: The moon will begin to pass before the sun at 10:12 AM MDT, beginning as a small, dark "bite" from the sun's upper right edge. At maximum (11:30 AM MDT), 97% of the
sun's disk will be covered. The last bit of the lunar silhouette will disappear from the sun's lower left edge at 12:54 PM MDT. Throughout this time, proper solar
filters must be used to protect the eyes from damage when looking at the sun. The danger is that it's possible to look directly at a mostly-dimmed sun for longer than
normal without discomfort, which allows more damage to occur. This is especially hazardous for young children, who may stare at the sun without experiencing the
instinctual urge to blink or look away.
Q8: How close does the path of totality come to Twin Falls, ID?
|Probability of morning (top) and afternoon (bottom) cloud cover for late August, based on historical data (by Jay Anderson, using data from CIMSS/NOAA/UW-Madison).
A8: Sun Valley is the nearest populated place to Twin Falls which will experience a total eclipse. However, Sun Valley lies just inside the southern border of the
65-mile-wide shadow, and thus will only see 62 seconds of totality, vs. 2 minutes, 13 seconds of totality along the center line, just south of Stanley. In Sun Valley,
the center of the moon (which will appear black) and the (obscured) sun will not coincide at mid-eclipse (the moon's center will pass to the north of the sun's). Sun
Valley and Stanley, for all their scenic beauty, are poor prospects for viewing this eclipse based on the historical probability of cloudless skies in late mornings in
August (45%-56%) compared to locations to the west or east (around 57%-63%).
Q9: Where will be the best place in Idaho to view this eclipse?
|The Aug. 21st, 2017 solar eclipse's path of totality over Idaho (by Fred Espenak, NASA's GSFC). Note that regions outside the blue curves will
only experience a partial eclipse whose maximum obscuration and duration diminishes with increasing distance from this path.
A9: Weather is the most important factor when choosing a viewing location. Based on historical data, eastern Idaho (near Rexburg) and western Idaho (near Weiser) appear
to offer the highest probability of clear skies within the state. However, statistics being what they are, the most prudent strategy would be to be as flexible as
possible as to where you intend to travel based on forecasts in the days leading up to the eclipse. (If both eastern and western Idaho look equally good, eastern is
preferable, since totality will last a few seconds longer there, and there is a more extensive road network to make it easier to relocate quickly to escape a small cloud
blocking the sun at eclipse time.) Be aware that overnight accommodations along the entire path of totality have largely filled up as of late 2016.
|Timeline for the total solar eclipse as viewed from the center line of the shadow path, 4 mi. south of Rexburg, ID (all times are Mountain Daylight Time).
Eclipse will occur earlier/later for locations to the west/east, respectively:
||Eclipse begins (partial phases, solar filters required for safe viewing)
|11:33:04 AM (approx.)
||Appearance of Baily’s beads, followed by diamond ring effect
||Start of totality (eclipse may be safely viewed directly without filters)
||End of totality, reappearance of the diamond ring and Baily's beads, after which filters must be used for safety
||Partial phases end
Q10: Can I safely view the eclipse's partial phases through a welder's helmet (or welder’s glass)?
|Regular sunglasses, welder's helmets/glass, photographic film, and looking through a pinhole are NOT safe ways to view a solar eclipse!
A10: While the darkest welder's glass (#14) is safe for solar viewing, most welder's helmets use filters that are insufficiently dark (and therefore, are not safe to view a
partial eclipse). Remember, lack of pain does not equate to lack of eye damage! By using an inadequate filter, it's possible to look at the sun for prolonged
periods without discomfort, compounding the damage. Even if using an inadequate filter does not result in immediately-obvious damage (ranging from permanent blind spots
to total blindness), it will likely result in the premature onset of cataracts.
Q11: Can I safely view the eclipse's partial phases through an electronically-darkening welder's helmet?
A11: Most electronically-darkening welder's helmets either don't darken enough, or are designed to trigger from the welding arc, but not sunlight. With safe "solar
shades" both available and inexpensive (typically costing less than $5), why risk it?
Q12: If #14 welder's glass is safe for viewing the eclipse, can I just use two #7 filters stacked together?
A12: No! The darkness rating on welder's glass is not based on a linear scale, so two #7 filters (or any other combination of filters that add to 14) will not provide
adequate protection and could result in permanent eye damage.
Q13: Can I look through photographic film to safely view the partial phases?
A13: Fully exposed, properly developed black-and-white negative film can provide the necessary filtering, but given how rare photographic film has become (black-and-white
even more so), why not be certain (and safe!) and simply used an approved solar filter?
Q14: Can I look through a pinhole to safely view the partial phases?
A14: No! A pinhole should only be used to project
the partially eclipsed sun onto a white surface (click
to download plans and classroom exercises (Microsoft Word document)). Looking through a pinhole will not only
make it impossible to see the eclipse, but it could also result in eye damage. (A safe, dramatic way to project the partially eclipsed sun is through a sheet of peg
board, producing hundreds of "crescent sun" images.)
Q15: Can I safely view the eclipse's partial phases with sunglasses, by not looking directly at it, or squinting?
A15: No! Regular sunglasses will only make it more comfortable to look longer, and thus incur more eye damage. They do not provide adequate eye protection, even
from a mostly-obscured sun. Looking to the side of the partially-eclipsed sun will only serve to damage a part of your eye other than the center of the visual field—
don't do it! And squinting will not significantly reduce the damage, either.
Q16: Where can I get a safe filter for viewing the partial phases?
|"Solar shades" are inexpensive (typically less than $5), widely available, and safe (just don't try to use them with an unfiltered telescope or binoculars!).
A16: "Solar shades" (good only for viewing the sun, since they are too dark to let you see anything else) are readily available from a number of vendors, including the
Herrett Center Store
. They resemble the disposable cardboard 3-d glasses used in movie theaters, but contain a special film that dims
the sun and absorbs the harmful infrared and ultraviolet light for safe direct viewing.
Q17: Can I use a telescope or binoculars to safely look at the partially-eclipsed sun if I'm wearing "solar shades?"
A17: No! Binoculars and telescopes concentrate the sun's light, and would quickly melt through a solar shades' plastic film, resulting in eye damage.
Q18: How can I view the eclipse safely with a binoculars or telescope?
A18: Some older telescopes included a solar filter which fit over the eyepiece. Because such filters were prone to getting knocked off, or cracking due to the
concentrated solar energy, they are considered unsafe and should be discarded. A proper, safe solar filter for binoculars or a telescope must fit securely over the end
of the instrument so that sunlight is dimmed to a safe level before it ever enters the optics. Such filters are readily available from a number of vendors. During
totality, it is safe to view the eclipsed sun with unfiltered binoculars and telescopes, but great care must be taken to point them away or put filters back on before the sun
begins to re-emerge from behind the moon!
Q19: For safety, shouldn't I just keep my kids inside during the eclipse?
A19: While parents and guardians must ultimately weigh the benefits vs. risks of allowing their children to view a solar eclipse (as we do with all other aspects of modern
life, including riding in automobiles), a solar eclipse is one of nature's great visual spectacles, and with a little bit of planning and preparation (see above), the risk
can be reduced to acceptable levels so everyone can safely enjoy this amazing event.
Eclipses Past and Future
Q20: When did a solar eclipse's path of totality last come through Idaho?
A20: Feb. 26th
, 1979 was the last total solar eclipse in Idaho
. It swept along
the Oregon-Washington border, through Idaho's panhandle, and along the length of central Montana before sweeping northeast into Canada. Being in wintertime, many
Idahoans were clouded out for this event.
Q21: When did a solar eclipse's path of totality last come this close to Twin Falls, ID?
A21: The solar eclipse of Jun. 8th, 1918
was the last total solar eclipse whose shadow
path came this close to Twin Falls. The center line passed near Weiser, Hailey, and Pocatello on its way through the Gem State.
Q22: When will a solar eclipse's path of totality next come this close to Twin Falls, ID?
A22: An eclipse shadow path won't come closer to Twin Falls than the 2017 eclipse until December
, when Twin Falls will lie quite near the center line. (Remarkably, for the next total solar eclipse after that, less than two years later, Twin
Falls will again
lie near the center line, on May 17th
, 2254.) For those who can't wait around until the 23rd
Century, on August
, 2045 a total solar eclipse
similar to the 2017 eclipse will follow a somewhat
more southerly path, sweeping through northern Nevada and northern Utah.
Q23: When will there be another total solar eclipse in Idaho after 2017?
A23: The next total solar eclipse in the Gem State
won't be until June 25th
(when the path of totality will pass north of Jerome).
Q24: When will the next total solar eclipse occur anywhere on Earth?
A24: Solar eclipses (either partial or total) occur somewhere in the world approximately every six months. However, total eclipses are roughly three times rarer than
partials; the last solar eclipse of any kind before the August 21st
, 2017 total eclipse across the U.S. was an
annular ("ring of fire") eclipse
which crossed from the southeastern Pacific, across the
southern tip of South America, across the southern Atlantic, to southern Africa on February 26th
, 2017. Four partials
, and 1/6/2019
none of which will be visible in the Contiguous 48 U.S. States) follow the 8/21/2017 eclipse before the next
, which will cross the South Pacific and southern South America on July 2nd
Q25: When will the next total solar eclipse occur in the Contiguous 48 States after 2017?
|The next total solar eclipse in the Contiguous ("Lower") 48 States after 2017 will be on April 8th, 2024 (by Fred Espenak, NASA's GSFC).
A25: On April 8th
, 2024, a total solar eclipse
will sweep from western Mexico,
through eastern Texas, and all the way to eastern Maine and the Maritime Provinces of Canada.