Updated Safety Advice for Viewing the August 21st Solar Eclipse

In response to alarming reports of potentially unsafe eclipse viewers flooding the market as the coast-to-coast solar eclipse of August 21st draws near, the American Astronomical Society (AAS) has revised some of its safety advice to the public.

safety-adviceHow can you tell if your “eclipse glasses” or handheld solar viewers are safe? It is no longer sufficient to look for the logo of the International Organization for Standardization (ISO) and a label indicating that the product meets the ISO 12312-2 international safety standard for filters for direct viewing of the Sun’s bright face. Why not? Because it now appears that some companies are printing the ISO logo and certification label on fake eclipse glasses and handheld solar viewers made with materials that do not block enough of the Sun’s ultraviolet, visible, and infrared radiation to make them truly safe. Some sellers are even displaying fake test results on their websites to support their bogus claim of compliance with the ISO safety standard.

Given this unfortunate situation, the only way you can be sure your solar viewer is safe is to verify that it comes from a reputable manufacturer or one of their authorized dealers. The AAS Solar Eclipse Task Force has been working diligently to compile a list of such vendors, now posted on its Reputable Vendors of Solar Filters & Viewers page. Task-force members have checked manufacturers’ ISO paperwork to make sure it is complete and that it comes from an accredited testing facility, and they’ve asked manufacturers to identify their authorized resellers and dealers to identify the source of the products they’re selling. Only when everything checks out does the AAS add a vendor to its listing.

“If we don’t list a supplier, that doesn’t mean their products are unsafe,” says AAS Press Officer and task-force representative Rick Fienberg. “It just means that we have no knowledge of them or that we haven’t convinced ourselves they’re safe.”

How can you tell if your solar viewer is NOT safe? The only thing you can see through a safe solar filter from a reputable vendor is the Sun itself. If you can see ordinary household lights through your eclipse glasses or handheld viewer, it’s no good. Safe solar filters produce a view of the Sun that is comfortably bright (like the full Moon), in focus, and surrounded by black sky. If you glance at the Sun through your solar filter and find it uncomfortably bright, out of focus, and surrounded by a murky haze, it’s no good. You should contact the seller and demand a refund or credit for return of the product, then obtain a replacement from one of the sources listed on the AAS’s reputable-vendors page.

What if you received eclipse glasses or a handheld solar viewer from a relative, friend, neighbor, or acquaintance? If that person is an amateur or professional astronomer — and astronomers have been handing out eclipse viewers like Halloween candy lately — they’re almost certainly ISO-compliant, because astronomers get their solar filters from sources they know and trust (in other words, from the ones listed on the AAS’s reputable-vendors page). Ditto for professional astronomical organizations, including college and university physics and astronomy departments, and amateur-astronomy clubs.

If you bought or were given eclipse viewers at a science museum or planetarium, or at an astronomy trade show, again you’re almost certainly in possession of ISO-compliant filters. As long as you can trace your filters to a reputable vendor or other reliable source, and as long as they have the ISO logo and a statement attesting to their ISO 12312-2 compliance, you should have nothing to worry about. What you absolutely should NOT do is search for eclipse glasses on the internet and buy whatever pops up in the ads or search results. Check the AAS list of reputable vendors and buy from one of them.

The AAS continues to emphasize that it is perfectly safe to look directly at the Sun during the brief total phase of the solar eclipse (“totality”), when the Moon entirely blocks the Sun’s bright face. On August 21stthis will occur only within a roughly 70-mile-wide path spanning the country from Oregon to South Carolina, and only for up to 2 minutes 40 seconds. Before and after totality, or throughout the entire eclipse if you’re outside the path (in which case you’ll see only a partial eclipse, which is nowhere near as exciting or magnificent as a total one), the only safe way to look directly at the Sun is through special-purpose solar filters. These are commonly sold as paper- or plastic-framed eclipse glasses or cardboard solar viewers that you hold in your hand. Ordinary sunglasses, even very dark ones, are not safe for looking directly at the Sun; they transmit many thousands of times too much sunlight.

Here are the AAS’s instructions for the safe use of eclipse glasses and handheld solar viewers (https://eclipse.aas.org/eye-safety):

* Always inspect your solar filter before use; if scratched, punctured, torn, or otherwise damaged, discard it. Read and follow any instructions printed on or packaged with the filter.

* Always supervise children using solar filters.

* If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them, or hold your handheld viewer in front of them.

* Stand still and cover your eyes with your eclipse glasses or solar viewer before looking up at the bright Sun. After looking at the Sun, turn away and remove your filter — do not remove it while looking at the Sun.

* Do not look at the uneclipsed or partially eclipsed Sun through an unfiltered camera, telescope, binoculars, or other optical device.

* Similarly, do not look at the Sun through a camera, a telescope, binoculars, or any other optical device while using your eclipse glasses or handheld solar viewer — the concentrated solar rays could damage the filter and enter your eye(s), causing serious injury.

* Seek expert advice from an astronomer before using a solar filter with a camera, telescope, binoculars, or any other optical device; note that solar filters must be attached to the front of any telescope, binoculars, camera lens, or other optics.

* If you are inside the path of totality, remove your solar filter only when the Moon completely covers the Sun’s bright face and it suddenly gets quite dark. Experience totality, then, as soon as the bright Sun begins to reappear, replace your solar viewer to look at the remaining partial phases.

* Outside the path of totality, you must always use a safe solar filter to view the Sun directly.

Some eclipse glasses and solar viewers are printed with warnings stating that you shouldn’t look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 international safety standard, which was adopted in 2015. If your eclipse glasses or viewers are relatively new and are ISO 12312-2 compliant, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren’t scratched, punctured, or torn, you may reuse them indefinitely.

What about welding filters? The only ones that are safe for direct viewing of the Sun with your eyes are those of Shade 12, 13, or 14. These are much darker than the filters used for most kinds of welding. If you have an old welder’s helmet around the house and are thinking of using it to view the Sun, make sure you know the filter’s shade number. If it’s less than 12 (and it probably is), don’t even think about using it to look at the Sun. Many people find the Sun too bright even in a Shade 12 filter, and some find the Sun too dim in a Shade 14 filter — but Shade 13 filters are uncommon and can be hard to find. The AAS’s Reputable Vendors of Solar Filters & Viewers page doesn’t list any suppliers of welder’s filters, only suppliers of special-purpose filters made for viewing the Sun.

An alternative method for safe viewing of the partially eclipsed Sun is indirectly via pinhole projection. For example, cross the outstretched, slightly open fingers of one hand over the outstretched, slightly open fingers of the other, creating a waffle pattern. With your back to the Sun, look at your hands’ shadow on the ground. The little spaces between your fingers will project a grid of small images on the ground, showing the Sun as a crescent during the partial phases of the eclipse. Or just look at the shadow of a leafy tree during the partial eclipse; you’ll see the ground dappled with crescent Suns projected by the tiny spaces between the leaves.

Press Release by the American Astronomical Society (AAS)

SWRI Team to Use Airborne Telescopes to Study Sun and Mercury During Total Solar Eclipse

EclipseA team led by the Southwest Research Institute (SwRI) will use airborne telescopes aboard NASA research aircraft to study the solar corona and Mercury’s surface during this summer’s total solar eclipse. The August 21 observations will provide the clearest images to date of the Sun’s outer atmosphere and attempt the first-ever “thermal images” of surface temperature variations on Mercury.

Total solar eclipses are unique opportunities for scientists to study the hot atmosphere above the Sun’s visible surface. The faint light from the corona is usually overpowered by intense emissions from the Sun itself. During a total eclipse, however, the Moon blocks the glare from the bright solar disk and darkens the sky, allowing the weaker coronal emissions to be observed.

“By looking for high-speed motion in the solar corona, we hope to understand what makes it so hot. It’s millions of degrees Celsius, hundreds of times hotter than the visible surface below,” said Dr. Amir Caspi, principal investigator of the project and a senior research scientist in SwRI’s Boulder, Colorado, office. “In addition, the corona is one of the major sources of electromagnetic storms here at Earth. These phenomena damage satellites, cause power grid blackouts, and disrupt communication and GPS signals, so it’s important to better understand them.”

Why is the Sun’s outer atmosphere so much hotter than its surface? Perhaps the Sun’s magnetic field carries energy into the corona and converts it into heat. Or perhaps nanoflares or nanojets — explosions or eruptions too small and numerous to see individually — are constantly releasing small amounts of energy that combine to heat the entire corona. The team will use high-speed, high-definition video of the corona to look for fast, coherent motions that could help solve this puzzle. The project may also shed light on another question: why the magnetic structures in the corona are relatively smooth and stable.

“The magnetic field forms well organized loops and arcades in the lower corona, as well as large, fan-shaped structures extending out to many solar radii,” said Dr. Craig DeForest, a co-investigator also from SwRI’s Boulder office. “These structures are constantly being churned and tangled by the motion of the solar surface itself. So why does the corona always appear well organized, like a recently-coiffed head of hair, and not snarled or matted?”

From two of NASA’s WB-57 research aircraft, the team will observe the corona during the eclipse using stabilized telescopes with sensitive, high-speed, visible-light and infrared cameras at 50,000 feet. This high altitude provides distinct advantages over ground-based observations.

“Being above the weather guarantees perfect observing conditions, while being above more than 90 percent of Earth’s atmosphere gives us much better image quality than on the ground,” said another SwRI co-investigator, Dr. Constantine Tsang. “This mobile platform also allows us to chase the eclipse shadow, giving us over 7 minutes of totality between the two planes, compared to just 2 minutes and 40 seconds for a stationary observer on the ground.”

These are the first astronomical observations for the WB-57s. Southern Research, which is located in Birmingham, Alabama, built the Airborne Imaging and Recording Systems onboard and is working with the scientific team to upgrade its DyNAMITE telescopes on both planes with solar filters and improved data recorders.

“This airborne platform also provides us with higher-quality, higher-speed images than are achievable from current or previous space-borne instruments,” said Caspi. “It highlights the potential of the WB-57 platform for future astronomical observations.”

Eclipse observations also give the team a unique opportunity to study Mercury, the planet closest to the Sun. Mercury is difficult to observe because it is usually washed out by the bright daytime sky, or distorted by the atmosphere near the horizon at twilight.

“We plan to measure Mercury in the infrared, in near darkness, and through very little atmosphere,” Tsang said. Scientists hope to use infrared measurements to calculate surface temperatures over the planet’s entire night side. “How the temperature changes across the surface gives us information about the thermophysical properties of Mercury’s soil, down to depths of about a few centimeters, something that has never been measured before.”

The SwRI-led team includes scientists from the University of Colorado, the National Center for Atmospheric Research High Altitude Observatory, and the Smithsonian Astrophysical Observatory, as well as international colleagues at Trinity College Dublin in Ireland and the Royal Observatory of Belgium. The team will make its data available to the public after the event. The team’s work will also be featured in two documentaries to air on eclipse day and in the fall of 2017.

Press Release from Southwest Research Institute

A Pinhole Viewer by any Other Name

Colander Pinhole Viwer

As we discussed in the February 22 blog, solar eclipses may be indirectly viewed in a variety of ways. One of the simplest and least expensive (often coming at no cost) is to create a projected image of the Sun through a pinhole viewer. This may be accomplished by simply poking a small hole in a piece of cardboard, and then holding the cardboard such that the sunlight passes through the hole and falls onto a viewing surface (a white piece of paper, sidewalk, garage door, etc.) To focus the image, the observer simply moves the cardboard farther or nearer from the viewing surface.

Eclipse Pinhole Viewer
Jenny Oh/KQED

Observers can get pretty creative with such pinhole viewers, devising a pattern of holes that spells out a word or forms a familiar shape like a heart.

 

“One of the simplest and least expensive ways to view an eclipse is to create a projected image of the Sun through a pinhole viewer.”

Colander Pinhole Viewer
Frederic of Attic Self-Storage Blog

Another version of a pinhole viewer, one that needs no preparation, may be found in most kitchens. This is a colander, whose numerous holes are usually a perfect size to project the sun’s image.

While pinhole viewers are not useful during totality (you want to be looking at the eclipsed sun at this time anyway) they are perfect for easily seeing the partial phases of a solar eclipse.

By Kevin Schindler, Lowell Observatory Historian

How To Know If Your Solar Glasses Are Certified

The Lowell Solar Eclipse Experience Solar GlassesIn our February 22 blog, we reviewed various methods of safely viewing the Sun during its partial phases of eclipse. One of these is by use of solar glasses (also called solar viewing glasses) that are simple to use, safe, and inexpensive.

Solar glasses usually consist of cardboard frames (more expensive ones are made of sturdier plastic) that hold a Mylar or, more typically, black polymer material that filters out harmful solar rays.

The International Organization of Standardization (ISO)—a worldwide body that sets standards for commercial and industrial products and processes—addresses safe viewing of the Sun in the

ISO 12312-2 standard (this is often listed more specifically as ISO 12312-2:2015). For solar eclipse glasses to be certified under this benchmark, they must block ultraviolet and infrared light as well as reduce visible light to safe and comfortable levels.

“If solar eclipse glasses are not marked as meeting the ISO standard, you’re better off not using them.”

Glasses that meet this standard should be marked as such (something like “Meets the requirement for ISO 12312-2:2015”). Safety is paramount with solar viewing, so if solar glasses are not marked as such, you’re better off not using them.

Rainbow Symphony is one company that has certified its solar glasses meet the ISO standard. This California-based manufacturer of 3D, eclipse, diffraction, and other varieties of glasses has produced the solar eclipse glasses that all participants at the Lowell Observatory Solar Experience will receive.

By Kevin Schindler, Lowell Observatory Historian

Stargazing During the Eclipse

Viewing planets and stars is usually a nighttime activity, experienced after the Sun has set and the ensuing darkness allows for these jewels to be seen. But the disappearance of sunlight during a total solar eclipse can result in a similar, albeit more short-lived, opportunity for stargazing. During this year’s August 21 eclipse, for instance, four different planets and several familiar constellations will shine ever-so- briefly during totality.

Eclipse Stargazing 2017
The eclipse view from Central Oregon. Made with Stellarium

During this year’s August 21 eclipse, four different planets and several familiar constellations will shine ever-so- briefly during totality.

Planets and Constellations

The brightest object to show itself, Venus, will become visible about 15 to 30 minutes before totality sets in. It will lie 34º west (to the right) of the darkening Sun (1º is about the width of your pinkie finger held at arm’s length, and 10º is the width of your fist held in the same way; thus, Venus will be a little more than three fist widths to the west of the Sun). It will stay visible until 15 to 30 minutes after totality ends.

Fainter Jupiter, located 52º east (to the left) of the Sun, should also become visible during the latter stages of partial eclipse for some observers east of Idaho, but it will be very low on the eastern horizon. It won’t have risen yet as seen west of Idaho so won’t be visible in that area. Some 30 seconds before and after totality, two other planets will be visible, though they will be more difficult to distinguish because of their faintness. Reddish Mars will be only 8º to the west of the Sun, while even fainter Mercury will be 11º southwest of the Sun.

As for constellations, the Sun will be in Leo during totality. Its brightest star, Regulus, may or may not be easy to see, depending on the glare from the nearby Sun’s corona during totality. Other bright stars that should be easier to see include Sirius (in Canis Major) and Rigel (in Orion), both to the west of the Sun; Capella (in Auriga and northwest of the Sun); and Arcturus (in Bootes and to the northeast of the Sun). The Big Dipper will also shine brightly, due north of the Sun.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

What You’ll See During the Total Solar Eclipse

While totality will mark the crowning moment of the August 21 solar eclipse, several other phenomena leading up to this much-anticipated climax will be worth experiencing. The entire sequence will be an enchanting, multisensory encounter with one of nature’s sublime spectacles.

At the Lowell Observatory Solar Eclipse Experience in Madras, Oregon, the fun starts at 9:06:42 a.m., when the Moon takes its first bite out of the Sun in a moment called 1st contact; that signals the beginning of the eclipse. Using a filtered telescope, solar glasses, or other appropriate observing techniques, observers will be able to see more and more of the Sun covered during the approximately 73-minute transition from partial to total eclipse.

Totality of Solar EclipseAt about 10 a.m.—20 minutes before totality begins—the visible part of the Sun will have shriveled to almost a point (rather than a disc), resulting in sharper shadows. Soon, when about 85% of the Sun is covered, the sky will have darkened to the point that the planet Venus will be visible with the unaided eye, 34 degrees to the northwest of the Sun. At about 10:10 am, fainter Jupiter will be visible, a little more than 50 degrees southeast of the Sun.

Soon, the darkening sky will make those witnessing the eclipse feel like night is falling, though the darkest part of the sky will be toward the Sun, rather than at the distant horizon. Observers may notice that birds will stop singing and other daytime animals will cease activity, as if night has truly arrived. Just like at actual nightfall, this time of silence might then be followed by the sounds of crickets, cicadas, frogs, and other nocturnal critters. The temperature will also drop, perhaps up to 15 degrees or so.

At about 10:19:32 a.m.—two seconds before totality begins—the appearance of Bailey’s beads will quickly transition to the brief display of the diamond ring, and then totality begins, designated as 2nd contact. This will last until 10:21:36 (3 rd contact). During totality, the best view is with the unaided eye, looking at the totally eclipsed Sun and also at the so-called 360 degree sunset (all horizons will display sunset colors).

During the exciting buildup to totality, it’s easy to miss some of the features described above. Luckily, they will all be apparent, in opposite order, when totality ends and the Sun is again only partially eclipsed. Slowly, the Moon will move out of our line of sight with the Sun until 11:41:03 (4 th contact), when the eclipse ends.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

Archaeological Evidence of a Total Solar Eclipse

Many observers of this year’s total solar eclipse will undoubtedly want to capture this extraordinary event by photographing or sketching it. Evidence at an archaeological site in New Mexico suggests that a witness to a similar event nearly a millennium ago did the same thing. The medium was rock, and that observer created a rock carving called a petroglyph by chipping away rock with a stone chisel.

Archaeological Petroglyphs in Chaco Canyon.

The petroglyph is on the south side of a free-standing rock in Chaco Canyon, just a few hundred yards from the Chaco Culture National Historical Park visitor center (this is some 102 miles northwest of Albuquerque, as the crow flies.) Scholars have referred to the rock as Piedra del Sol (“Sunstone”) because it contains several Sun-related features typically found in archaeological remains, including a spiral petroglyph apparently used to mark the location of the Sun on the summer solstice. But the alleged solar eclipse petroglyph is especially compelling because total solar eclipses are rare for any given location.

Eclipse Petroglyph Chaco Canyon
Petroglyph allegedly depicting a solar eclipse.

The petroglyph consists of a filled-in circle with curlicues shooting out from its perimeter. While other petroglyphs are nearby, a smaller, filled-in circle to its upper left has been

interpreted by some scientists as representing the planet Venus, which would have been visible once the Sun darkened during eclipse.

The curlicues may represent the Sun’s corona and, perhaps, coronal mass ejections (CMEs), which are abnormally large concentrations of plasma released from the corona. These CMEs are more common during times of peak solar activity, which generally follows an 11-year cycle.

eclipse sketch
Modern Day Sketch from the 1800s depicting the Corona and Corona Mass Ejection.

So, do the observations and inferences match the astronomical facts? Determining the time and location of past and present eclipses is fairly straightforward, and we know that a total solar eclipse was visible from Chaco Canyon on July 11, 1097, during the height of the Chaco culture. Research has also shown that this eclipse happened during peak solar activity. Finally, astronomers can easily ascertain the relative position of the planets and other celestial bodies in past years, and this circle is indeed in the proper position for Venus, relative to the Sun, for July 11, 1097.

We will likely never know for sure whether this petroglyph really does represent a total solar eclipse, but there is sufficient evidence to keep our curiosity alive.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

Accessories of the 2017 Total Eclipse: Beads and Rings

During totality of the 2017 total solar eclipse, viewers will enjoy the rare opportunity to see the Sun’s corona, a complex region of extremely hot plasma extending far above the solar surface. But this won’t be the only unusual thing to see, as the first and last moments of the eclipse will be marked by two brief, spectacular phenomena— Baily’s Beads and the Diamond Ring Effect.

Leading up to totality, the Moon gradually moves in front of the Sun. Just before completely blocking it, a few rays of the Sun shine through valleys and other irregularities on the lunar limb (the edge of the Moon, as seen from Earth), resulting in a few bright beads of light called Baily’s beads. This feature is named after English astronomer Francis Baily, who in 1836 explained the nature of the phenomena. As with many cases in science, Baily was not the first person to observe or explain the effect; that honor goes to Baily’s countryman Edmond Halley in 1715.

The beads will be visible for only a short time; the last one glows brightly and looks like the diamond on a ring, and is thus known as the Diamond Ring Effect. Later, as the Sun comes out of eclipse, the Diamond Ring Effect and Bailey’s beads will again be visible. Both Baily’s beads and the Diamond Ring Effect are short-lived but dramatic and worth seeing.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

How to Safely View the Sun During a Solar Eclipse

The eclipsed Sun may be viewed in a variety of ways, and several of these don’t even require any sort of expensive equipment. In all cases, safety is of prime importance and, while observing is generally pretty simple, proper care should always be taken. Here are a few of the more common methods.

  • During partial eclipse. Most of us grew up hearing the mantra, “never look at the Sun,” though we can modify this to “never look at the Sun without proper eye protection”. This is important to remember while viewing a solar eclipse. Even when the Sun is 99% eclipsed, its intensity is still more than enough to cause permanent eye damage.
Direct Observations
  • Solar Eclipse Glasses. These are inexpensive (usually only a dollar or two) and very easy to use. You can order them online from a variety of suppliers. Lowell Observatory will also have them available at the Lowell Eclipse Experience.
  • Filtered telescopes, binoculars, or cameras. These use special filters that block out the harmful Sun rays. Several astronomers and educators will operate these instruments at the Lowell Eclipse Experience.
  • Welders Goggles – Must have a rating of 14 or higher. These should not be used in conjunction with any magnifying instruments such as telescopes or binoculars, since those will intensify the sunlight and can cause the goggles to break from the intense heat.
Indirect Observations

eclipse-projection

  • Pinhole Viewers. These allow observers to view a projected image of the Sun. A simple option involves two thin pieces of cardboard – one will be used to channel the sunlight, the other will act as a viewing screen. On one piece, poke a small hole (the size of a pin; thus the name!) through it. With your back to the Sun, hold it so the sunlight passes through and then position the other piece behind it, so that the Sun’s image falls onto it. This image will be a small, an inverted view of the Sun, and you can make the image larger or smaller by adjusting the distance between the two pieces of cardboard. Nature often creates such pinhole viewers for us, in the form of trees. As seen in the accompanying picture, captured at Lowell Observatory during a 2012 partial solar eclipse, clumping leaves or pine needles act in the same way as the pierced cardboard, leaving images of the Sun projected on a garage door.
  • Projections from telescopes or binoculars. With the instrument mounted on a tripod and pointing at the Sun, sunlight will shine through the eyepiece onto a piece of paper, which serves as an observing screen.
During Totality
  • Remember to “never look at the Sun without proper eye protection”. Well, during totality, the Moon completely blocks the Sun from our view so you can then safely look in its direction without any eye protection. You will see the darkened outline of the Moon surrounded by the shimmering glow of the solar corona. While viewing can be done through telescopes, binoculars, or cameras (with their filters temporarily removed), the best way to observe totality is to simply gaze up and enjoy the experience, without trying to fiddle with those instruments. By the time totality ends (at the Lowell Eclipse Experience, an official will announce over a loudspeaker when totality begins and ends), you’ll need to revert back to observing the partial phase with the methods described above.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian

Notable Total Solar Eclipses Throughout History

History's Solar EclipsesFor centuries, scientists have taken advantage of the special circumstances of total solar eclipses to learn about our solar system. More than 2,100 years ago, the Greek astronomer Hipparchus compared observations of such an eclipse made from different spots on Earth to calculate the distance between the Moon and Earth. His estimate of 268,000 miles is within about 11 percent of the actual distance, which is not bad considering the archaic observing techniques of the time.

In 1868, British astronomer Norman Lockyer and French astronomer Pierre Jules César Janssen independently discovered helium, the second most abundant element in the universe, while observing a total solar eclipse. Helium’s name derives from the circumstances of its discovery—the word helium comes from Helios, the Greek god of the Sun. Twenty-seven years would pass until scientists found helium on Earth.

The 2017 total solar eclipse will stretch across the United States, from the Pacific to Atlantic oceans. The last one to do this occurred on June 8, 1918. As for the 2017 eclipse, Lowell astronomers and other staff left Arizona in 1918 in order to observe the event. Observatory staff used a variety of instruments for this work, including two lenses–each with a diameter of five inches and focal length of 38.7 feet—borrowed from the U.S. Naval Observatory (these were two of the so-called “Transit of Venus objectives”, used to observe the transits of 1874 and 1882).

History of EclipsesMore famously, in 1919 British astronomer Arthur Eddington traveled to an island in the Pacific Ocean to photograph stars around an eclipsed Sun. Albert Einstein had predicted in his general theory of relativity that starlight would not travel in a straight line but instead bend slightly as it passed by an object, whose gravity would tug on the starlight. Eddington saw a perfect opportunity to test this prediction by observing and measuring starlight as it passed by the darkened Sun during a total eclipse. Eddington’s findings seemed to support Einstein’s prediction (later astronomers have debated the accuracy of Eddington’s measurements) and made Einstein an instant global celebrity.

By Kevin Schindler, Lowell Observatory Public Information Officer and Historian