This series details the eclipse-chasing exploits of our President and CEO, Chad Dorsey, as he heads down to Tennessee on a quest for the total solar eclipse. See the whole series.
We’re settled in Tennessee, awaiting totality. As we do, this final post in a three-part mini-guide describes the stages involved as totality nears and takes over, and the planning and prioritizing involved in experiencing and capturing it.
Eclipses are fascinating things. Every aspect of one is by definition practically a unique experience for almost everyone experiencing it. For that reason, the entire phenomenon usually leaves people not knowing what to expect. While this can be a very good thing, as experiencing the event for oneself in one’s own way is by all means the most important thing to do overall, there are a number of aspects of an eclipse that are especially wonderful to experience, and that veteran chasers look for in particular. Many of the most fascinating are fleeting or non-obvious to observe, and require either the knowledge of where or when to look or specific advance preparation to observe. I’ll list a few for those experiencing totality for the first (or the many-th) time as tips and to-dos for what to watch for in the hours and moments through totality today.
Early partial phases – Sunspots and the progressing crescent
The partial phases, especially the early partial phases, are the slow and unobtrusive portion of an eclipse. The slow buildup. The pre-game show. I think of them like the advertisements that show in the theater before a movie—nice to see and very worth watching off and on if you’re there, but not essential for continuous viewing. The partial phases are mostly cool for the overall realization that something’s eating the Sun! They are also an opportunity to observe some of the details of the Sun’s surface, in particular sunspot patterns. While the easiest way to observe an eclipse is through eclipse glasses, as noted in an earlier post, there are plenty of good ways to observe these partial phases relatively continuously. One of our favorite is to set up an unfiltered telescope pointing at the Sun and use it to project the Sun’s image on a screen (usually a piece of paper or tagboard) under the eyepiece.
This can easily generate an image around 2-3 inches in diameter, and allows a larger number of people to view the advancing partial phases simultaneously. Of course, it’s essential to keep others from attempting to look through the scope as it points at the sun. Also, since the image is highly magnified, the rotation of the Earth is highly evident—the image quickly moves across the screen, and will pass out of the scope view generally in a matter of minutes, so this method requires some consistent attention to realignment (or a motor drive, if you’re at the point of having even more specialized equipment). The early partial phases move along slowly, but consistently, so they shouldn’t be ignored—it’s great to see the moon begin to make a crescent across the sun over the first 45-60 minutes of totality. Note that this can also be done by holding up binoculars in reverse pointing toward the ground. *Don’t * look at them
Late partial phases — Crescents, eerie light and shadow bands
If the early partial phases of the eclipse are the movie theater advertisements before the lights go out, the late partial phases are the logos and opening credits for the blockbuster movie itself—and in this case, one you’ve waited over twenty years to see! In other words, the later partial phases are where it’s at. From about 30 minutes prior to totality up through totality’s onset, a continual parade of phenomena crop up and demand closer observation. Early on in this period, pinholes of all types begin to cast noticeable lit projections on surfaces below. Since these projections are images of the eclipsed Sun, they take on the shape of the remaining exposed region of the Sun at that moment, transforming the ground below a tree into a cavalcade of crescents. You can also try creating these yourself during the partial phases—a kitchen colander provides one fun way to do this—or even a Saltine cracker!
The lighting is the second effect noticeable during the later partial phases. Lighting can become odd and disconcerting during these moments, and changes by the minute. During the Baja eclipse, it felt as if someone were turning down a dimmable light everywhere, and colors became oddly muted in an otherworldly manner. We’ll be watching to see when these effects happen during this eclipse and how they change and evolve.
The last effect to watch for during the partial phases is a little-known and elusive one that veteran eclipse chasers always look for, but can require some preparation. In the minutes, or even seconds, prior to totality, some eclipse viewers report seeing wavy bands of shadow appear, typically dancing along light areas of the ground. These bands sometimes seem like more of a myth than a consistent phenomenon, as they are rarely captured well. Additionally, because they are so elusive, they are not easily studied and only partially understood. It appears that scintillation theory provides a good explanation of most of the effects observed related to shadow bands, and that their generation is related to turbulence in the lower areas of the atmosphere—below 2 km—in times longer than 20 seconds to from totality. In the final seconds prior to totality, the current theory holds that turbulence at the tropopause (20-60 km) may have influence over their formation as well. These remain strange and complex phenomena to understand, and vary greatly from eclipse to eclipse and location to location. Scientists are still hoping for better data about these with each eclipse. We’ll be placing a sheet out and watching carefully to see if we can help the cause!
Onset of totality — Diamond ring and Baily’s Beads
As totality rushes in, there are two specific effects that veteran eclipse chasers always look for and hope to see. The more well known of these is the “diamond ring effect,” which is often captured in the more iconic eclipse photos many people have seen. This effect, which appears as a ring of totality with a single bright spot in one location around the perimeter, can appear in the final seconds as totality is beginning and the initial seconds as totality slips away. This effect is one of the most gorgeous and memorable of a solar eclipse overall, and one every eclipse chaser hopes to see. It is also among the coolest as well because of the nature of its origin. The diamond ring effect is a subset of the larger class of effects entitled “Baily’s Beads,” named for astronomer Francis Baily, who first provided an exact explanation in 1836. These effects are so cool because they provide direct-observation evidence from Earth of the jagged profile of the lunar surface. That is, the diamond ring effect actually represents the sun’s light shining through a single valley on the moon’s surface! It’s worth noting that, although Baily gets his proper due in the naming, Edmund Halley actually first made the guess at the cause of this phenomena with his observations during the 1715 eclipse over a hundred years before Baily’s explanation.
Baily’s Beads, as named more generally, appear as small scattering of beads gathered in a group near one location on the perimeter of the circle. These necklace-like formations are typically delicate, beautiful and highly fleeting. It turns out that they are usually less generally observable by veteran eclipse chasers for an interesting reason: in eclipses viewed from the center of the eclipse path, they are typically only seen for a few seconds. However, at the edges of the path, where the curve of the moon’s shadow grazes the observation path, they can be observed for as long as 1-2 minutes. Of course, since totality at those locations only lasts a matter of seconds, and since traveling to the centerline 10-20 miles away typically brings totality lengths of minutes instead, very few eclipse chasers are interested in shortening their time under totality simply to observe Baily’s Beads for a longer time! Will we see either of these effects in today’s eclipse? We certainly hope so, and we’ll be watching carefully for both!
Totality arrives — Corona and prominences
The main show, and what raises goosebumps on every eclipse-watcher’s arms, is the glorious sight of totality itself. A major part of what makes it such a glorious sight is the appearance of the wispy, feathery corona visible extending unevenly in all directions from the central disc of totality. This corona, from the Latin for “crown,” is truly the crowning element of any eclipse, and is only truly visible during totality, making the event a particularly important time for scientific study. This year’s eclipse will be studied in particular by an intrepid group from the nearby Harvard-Smithsonian Center for Astrophysics, who will rise above the clouds in a plane—but not be able to see the eclipse themselves!—to study this year’s eclipse as it happens.
The corona is the Sun’s wispy outer atmosphere, made up of hot, ionized gases extending thousands of kilometers from the Sun’s surface. Because of the Sun’s ever-shifting magnetic fields, the corona is dynamic and ever shifting. The corona is best observed during eclipses for the simple (and obvious) fact that the Sun is so bright that its light swamps the corona’s at all other times. Though scientists can use a device called a coronagraph to artificially block the sun’s disc and view the corona at other times, the opportunity offered by an eclipse is still the gold standard for scientists—and the only opportunity for mere mortals—to view the corona’s evanescent beauty.
The corona is glorious for a few additional reasons. For one, it’s unpredictable. Well, mostly. With improved observation and theory available now, scientists are getting better at predicting how the corona will look. However, in reality, the corona’s appearance remains one of nature’s most wonderful mysteries, and one of eclipse watching’s best guessing games. The second thing that makes the corona so amazing is its temperature. Despite the fact that it extends thousands of miles away from the Sun’s surface, the corona is much hotter than the rest of the Sun itself. In fact, much hotter—three orders of magnitude, to be exact. Why? Yet another unsolved mystery (isn’t the corona awesome?!) that science is still working to unlock. The answer lies somehow in the fact that the corona contains a wealth of pent-up energy, which it releases by ionizing atoms in the corona sphere. This image of iron-poor atoms shows some of the different examples. How the energy gets from the Sun into the corona remains a mystery, however. With luck—and the help of thousands of specially prepared amateur astronomers at the ready as the shadow sweeps across the country—this year’s eclipse will offer some useful clues toward answering that question.
The last reason the corona is such an awesome aspect of a total eclipse is simply because it it so difficult to capture in any way other than with the naked eye. Because our eye is attuned to so many different variations in brightness, the subtle variations and faint structures within the corona’s feathery wisps are readily apparent and incredibly striking to those actively viewing a solar eclipse. However, cameras are only able to capture one exposure at a time. Taking in the whole of a corona’s detail can requires multiple photographs, and even the subtle stitching of HDR photos still only begins to capture the essence of the sight as viewed in person. In addition, the fluctuation of the Sun’s magnetic fields can lend a subtle dynamism to the corona during the viewing of a total eclipse. During the extremely long Baja eclipse, we saw the corona fluctuate at times, almost as if it were a slightly waving flag made of some gossamer material. Incidentally, the 1991 corona still stands out as the one to beat among eclipse watchers. Though we’re near the low point of the 11-year sunspot cycle this year, nobody knows what the corona will look like this time—but we’re waiting excitedly to see!
The last main feature of totality is the icing on the cake, and just as icing varies with every cake, this one varies radically from eclipse to eclipse. Prominences are large loop of plasma extending from the Sun’s surface, a fingery, fiery structure of charged hydrogen and helium gas contorted and buoyed by the Sun’s magnetic fields. Prominences are awesome, literally and figuratively. They exist first as growing magnetic instabilities on the Sun’s surface itself, then can erupt outward into structures that extend hundreds of thousands of miles from the surface and can sometimes persist for months. Prominences are sometimes—but not always—highly visible during totality. When they are visible, they appear as crimson-red beads or lines along the perimeter of totality’s inky black disc. Imagining these structures and the fiery vortices that underly them is one of the most exhilarating aspects of observing a solar eclipse. In the 1991 eclipse, several prominences were highly visible to the naked eye, with at least one extending far from the surface and into the feathery corona. We’re hoping for some interesting prominences this time, and will be observing both with our eyes and with binoculars and scopes to see if we can see them!
Following totality — A world in reverse
After totality completes, all of the phenomena of the partial phases are observable in reverse. However, they are much less excitedly observed—the time is taken up much more with wonder and exhilaration as everyone processes the fleeting moments of totality both together and alone. The moon’s disc quietly slips away, restoring the Sun to a complete circle once again, untouched and perfect, lying in wait for the next encounter 18 months or more in the future.
Totality’s big dilemma — Photograph, or soak it all in?
The biggest question of all, however, plagues all eclipse chasers. The above phenomena are all visible during totality, and capturing and sharing them is every eclipse-hound’s dream. However, executing on that plan can be a dangerous thing. Totality is extremely short and fleeting, and can surprise even the most veteran eclipse watcher. With an event as big as this one, Murphy’s Law is in full effect—anything that can go wrong usually will, in colossal fashion. During the Baja eclipse, my one job was to operate the video camera to catch video of the diamond ring effect. This I did nobly and with dedication—except that in the excitement I missed turning adjusting the camera’s iris to account for the sudden dim of totality (something not at all uncommon among eclipse documenters).
To get photography right takes planning, rehearsal and determination. It also can make the experience of totality one of stress and equipment, rather than joy and awe. Each eclipse carries its own goals and challenges, and each person watching needs to decide for him or herself how to approach this dilemma. In this case, I’ve decided in advance—with so many people out there taking professional photographs of totality, the Web will be flooded with enough gorgeous images to fill a hundred hard drives. Spending our short moments trying to capture the perfect picture isn’t worth missing out on the precious experience. The main dilemma I’d rather be faced with will likely be whether to stand at a telescope or just lie down and soak it all in!
So, with all these phenomena clearly in mind and our equipment beginning to move into place, nothing’s left now but the waiting—and nervous waiting it is! Nothing compares to the excitement of waiting and watching in the hours and seconds prior to a total solar eclipse. As we settle in, I’ll leave you with Mark Ryan’s amazing composite view of the 1991 eclipse’s amazing corona and prominences as a touchstone for what’s to come.