Deciphering a solar array surprise with Energy3D

Fig. 1: An Energy3D model of the SAS solar farm
Fig. 2: Daily production data (Credit: Xan Gregg)
SAS, a software company based in Cary, NC, is powered by a solar farm consisting of solar panel arrays driven by horizontal single-axis trackers (HSAT) with the axis fixed in the north-south direction and the panels rotating from east to west to follow the sun during the day. Figure 1 shows an Energy3D model of the solar farm. Xan Gregg, JMP Director of Research and Development at SAS, posted some production data from the solar farm that seem so counter-intuitive that he called it a "solar array surprise" (which happens to also acronym to SAS, by the way).

The data are surprising because they show that the outputs of solar panels driven by HSAT actually dip a bit at noon when the intensity of solar radiation reaches the highest of the day, as shown in Figure 2. The dip is much more pronounced in the winter than in the summer, according to Mr. Gregg (he only posted the data for April, though, which shows a mostly flat top with a small dip in the production curve).

Fig. 3: Energy3D results for four seasons.
Anyone can easily confirm this effect with an Energy3D simulation. Figure 3 shows the results predicted by Energy3D for 1/22, 4/22, 7/22, and 10/22, which reveal a small dip in April, significant dips in January and October, and no dip at all in July. How do we make sense of these results?

Fig. 4: Change of incident sunbeam angle on 1/22 (HSAT).
One of the most important factors that affect the output of solar panels, regardless of whether or not they turn to follow the sun, is the angle of incidence of sunlight (the angle between the direction of the incident solar rays and the normal vector of the solar panel surface). The smaller this angle is, the more energy the solar panel receives (if everything else is the same). If we track the change of the angle of incidence over time for a solar panel rotated by HSAT on January 22, we can see that the angle is actually the smallest in early morning and gradually increases to the maximum at noon (Figure 4). This is opposite to the behavior of the change of the angle of incidence on a horizontally-fixed solar panel, which shows that the angle is the largest in early morning and gradually decreases to the minimum at noon (Figure 5). The behavior shown in Figure 5 is exactly the reason why we feel the solar radiation is the most intense at noon.

Fig. 5: Change of incident sunbeam angle on 1/22 (fixed)
If the incident angle of sunlight is the smallest at 7 am in the morning of January 22, as shown in Figure 4, why is the output of the solar panels at 7 am less than that at 9 am, as shown in Figure 3? This has to do with something called air mass, a convenient term used in solar engineering to represent the distance that sunlight has to travel through the Earth's atmosphere before it reaches a solar panel as a ratio relative to the distance when the sun is exactly vertically upwards (i.e. at the zenith). The larger the air mass is, the longer the distance sunlight has to travel and the more it is absorbed or scattered by air molecules. The air mass coefficient is approximately inversely proportional to the cosine of the zenith angle, meaning that it is largest when the sun just rises from the horizon and the smallest when the sun is at the zenith. Because of the effect of air mass, the energy received by a solar panel will not be the highest at dawn. The exact time of the output peak depends on how the contributions from the incidental angle and the air mass -- among other factors -- are, relatively to one another.

So we can conclude that it is largely the motion of the solar panels driven by HSAT that is responsible for this "surprise." The constraint of the north-south alignment of the solar panel arrays makes it more difficult for them to face the sun, which appears to be shining more from the south at noon in the winter.

If you want to experiment further, you can try to track the changes of the incident angle in different seasons. You should find that the change of angle from morning to noon will not change as much as the day moves to the summer.

This dip effect becomes less and less significant if we move closer and closer to the equator. You can confirm that the effect vanishes in Singapore, which has a latitude of one degree. The lesson learned from this study is that the return of investment in HSAT is better at lower latitudes than at higher latitudes. This is probably why we see solar panel arrays in the north are typically fixed and tilted to face the south.

The analysis in this article should be applicable to parabolic troughs, which follow the sun in a similar way to HSAT.

Exploring hurricane datasets in the classroom

In August 2017, Hurricane Harvey evolved from a series of thunderstorms to one of the first major hurricane landfalls in the United States since early 2005. Right on the heels of Harvey, Hurricane Irma blasted through the Caribbean and onto the U.S. mainland, striking Florida in early September.

The National Oceanic and Atmospheric Administration (NOAA), which aims to understand and predict changes in weather, provides educational resources and datasets about hurricanes.

The dataset for 2005-2015 is available in our Common Online Data Analysis Platform (CODAP), a free and open-source web-based data analysis tool, geared toward middle and high school students.

Screenshot of NOAA hurricane data embedded in our Common Online Data Analysis Platform.

With all the current catastrophic news about hurricanes, students have lots of questions. Use the data to help them understand the history and characteristics of storms.

  • To investigate the paths that hurricanes generally follow, use the slider to change the year from 2005 to 2015, and watch the data points on the map, which represent the general path of the storms.
  • To determine the storm with the highest wind speed, click the top data point in the wind speed graph, which plots year against highest wind speed. Since data is linked across multiple representations, the data point is highlighted on the graph and in the table, so you can find the name and date of that particular storm (e.g., Wilma, October 15, 2005, with top wind speeds of 160 mph).
  • To learn which year had the most or least number of storms, look at the storms per year graph. Notice an outlier in the data with year 2005, which had 15 storms during that season. (Note: This was the same year as Hurricane Katrina. Select KATRINA in the table and make sure the slider is set to 2005, then see the path of the hurricane graphed on the map.)
  • To see a relationship between wind and pressure, click on the Graph button. Drag the Maximum Wind column header from the table to the vertical (y) axis until the axis turns yellow. Drag the Minimum Pressure to the horizontal (x) axis until the axis turns yellow. (Note: you may need to scroll to the far right of the Case Table to see these columns.) 

Analyzing and interpreting data is one of the key science and engineering practices of the Next Generation Science Standards (NGSS), and representing and interpreting data are featured throughout the Common Core State Standards (CCSS) for mathematics. Students can use publicly available datasets from storms and other weather events to learn more about the world around them.

STEM Resource Finder: Part I – Register for a Teacher Account and Add a Class

Our updated STEM Resource Finder (previously called the Learn Portal) at learn.concord.org now allows you to search for resources, create classes, assign activities, and track student progress with reports. All in one place. All for free.

Register for a Teacher Account

Follow these easy steps to create an account in the STEM Resource Finder.

  1. Click the Register button in the upper right-hand corner.
  2. Complete the registration form with your name and create a password.
  3. Select the radio button for “Teacher,” create a username, and provide an email address you can access easily.
    • Complete the fields about your location and school.
    • If you don’t find your school listed, or you are a homeschool, click “I can’t find my school in the list” to enter the name of your school.
  4. After registering, you’ll receive an email from help@concord.org. Click the “Confirm Account” button in the body of the email to activate your account.
    • If you do not receive the activation email in your inbox, please check your junk or spam mailboxes, or any quarantine set up by your email provider.
    • If you cannot access the email in your junk or spam mailboxes or quarantined email, please contact help@concord.org for assistance.
  5. By clicking the link in the activation email, you’ll be directed to the STEM Resource Finder. 
  6. Click the Home icon in the upper right — that’s your own home page, where you can create and manage your classes, and track student progress.

Add a New Class

  1. To get started, Add a New Class by clicking the link on the left and enter Class Setup Information. Provide a class name, description, and applicable grade level(s). (Note: Please disregard the Term field as it’s currently not working. We’re working to update this soon.)
  2. Create a unique Class Word, which students will use to enroll in this class. Class words can be more than one word, but cannot include any special characters (such as *, @, and %). The Class Word is not case sensitive.
  3. You’re now ready to assign resources to this class. Click the Concord Consortium logo in the upper left to search all resources or view curated collections of resources by clicking the Collections link in the top navigation bar.

Additional information is available in the User Guide.

Let us know if you have any questions!

Designer dragons? Talking to students about the ethical implications of editing DNA

University of Michigan School for Environment and Sustainability, Flickr (CC-BY-2.0)

A breakthrough in medical research has allowed a team of scientists to edit the DNA of human embryos to repair a version of a gene that causes cardiomyopathy, a genetic disease resulting in heart failure. While some see this genome editing technology—known as CRISPR—as a remarkable tour de force, others find the practice extremely alarming.

Meanwhile, some middle school students are already practicing genetic engineering in the classroom with inexpensive kits. Geniventure, our dragon genetics game for middle and high school students, also allows students to manipulate genomes, but the DNA in Geniventure is virtual and the species is a mythical creature called a “drake,” the model species for dragons.

Working with drakes and dragons allows us to combine various real-world genes without having to be restricted to the genome of a specific species, a problem that scientists in many countries often run into. We’ve combined real genes from mice, fruit flies, lizards, and other model organisms into the genome of our fantastical creatures. Students thus experience many of the same real genes that scientists around the world are also studying. Importantly, using dragons also allows teachers to talk about ethical issues, including the implications associated with modifying DNA.

CRISPR incites fears of designer babiesthe idea that parents will someday want to choose particular traits for their unborn children. In Geniventure, students do “design” drakes in challenges that require them to change alleles to match a target. Teachers guiding students through these challenges have an opportunity to discuss the notion of modifying an organism’s genes for a particular purpose. They can pose questions to get students thinking about the ethical implications of gene editing: Are there circumstances where you wouldn’t want to edit a drake’s genes? What might happen if you changed the wrong gene and you couldn’t change it back? What effect would that have on the drake’s future offspring?

“Designing” drakes. Geniventure tasks students with manipulating drake genes by selecting alleles from pull-down menus in order to match a target drake.

It’s easier to discuss these issues when we are talking about drakes and dragons because humans aren’t anything like these fictitious creatures. But since the genes are modeled after real genes (e.g., the the albino gene is modeled after skin color in humans), we can translate conversations about dragons to similar debates by scientists and regulatory officials about human gene editing. In Geniventure, students change an albino drake’s genes from producing a broken enzyme so that it can create a functional protein and generate a drake with color distributed throughout its scales. Albinism is also an inherited genetic condition in humans, so there is a significant parallel that could bridge the conversation.

Scientists are using CRISPR to investigate the prevention of inherited diseases like Huntington’s disease, cystic fibrosis, and even some cancers, though there is opposition and concern over this technology. One major fear is the safety to a developing embryo. DNA that’s been modified in an embryo would be passed down for generations, which raises concerns that any mutations as a result of the gene editing could cause new diseases and become a permanent part of that family’s genetic blueprint. Geniventure enables students and teachers to start discussions about these important topics.

Virtual CRISPR-like techniques engage students in editing dragon DNA

The CRISPR gene editing technique is faster, cheaper, and more accurate than past methods of editing DNA. And it’s creating a huge buzz in the world of science and medical research. By precisely removing, adding, or altering part of the genome, CRISPR enables geneticists to target and edit genes that are associated with genetic diseases—without affecting other areas of the genome, a major drawback of previous approaches.

A recent story (CRISPR, 5 ways) includes a video, produced by Wired magazine, in which a biology professor at NYU explains CRISPR to a seven-year-old, a high school student, a college student, a graduate student, and an expert scientist in the field of genetics. The conversations range from genomes to the value of basic research.

In the final conversation with the expert scientist, the focus shifts to the level of DNA and genome engineering. Scientists who use CRISPR must understand the underlying mechanisms by which the genes affect particular genetic traits and disorders. They’re able to learn about the composition and functionality of genes from model species they study and apply what they’ve learned to another target species (e.g., the mouse is a model species for human genetic disease).

We’ve created an online learning environment that allows middle and high school students to do the same.

Geniventure, dragon genetics software

Geniventure, the next generation of our popular dragon genetics software Geniverse, places students in a virtual underground lab where they perform genetic experiments with drakes, the model organism for dragons. There is real biology behind the mythical drake and dragon genes and traits, which have been carefully compiled from the actual genes and associated traits of the anole lizard, mouse, fruit fly, zebrafish, and other model species used to study genetics. The genes that affect horns, wings, color, and other drake traits are genes that are involved in the development and functioning of similar traits in real organisms.

In our Geniventure game, students zoom into a drake’s genes, see the actual DNA code behind them, and manipulate the resulting proteins as the proteins do the work of producing traits. The first set of protein-based challenges using this new interface revolves around scale color (modeled after the same genes for human skin color) and allows students to edit the genes of an albino drake. After working with the proteins that produce melanin and discovering a broken enzyme that results in an albino drake, students enter the nucleus of the cell to change the drake’s genes (and DNA) from producing the broken enzyme so that it can create the functional protein, ultimately generating a drake with color distributed throughout its scales.

From albino to charcoal (right). In the protein-level challenges, students can view the starting state of their drake’s scale color (Albino), the current state (Lava), and the target state (Charcoal). The Start and Target views also display the distribution of color throughout the drake’s scale cells.

Proteins in action. In the Geniventure Zoom Room, students experiment with proteins and discover how they influence the color of the drake. Students are tasked with manipulating the proteins of an albino drake to restore color to its scales.

Inside the nucleus. In some challenges, students are unable to work with the proteins directly. Instead, they must enter the nucleus where they can alter the drake’s alleles to create the proteins needed to reach the target color.

Making this protein-based link from DNA to trait is critical for students’ ability to make sense of patterns between genes and traits— for example, dominant vs. recessive versions of genes— and to apply the same logic to other genetic phenomena. Through Geniventure, students are able to transfer their experience of editing genes and working with proteins in drakes to an understanding of how scientists are using CRISPR and other techniques.

Our goal is to help students better understand modern science, including biotechnology advances such as CRISPR, to make science engaging and relevant, so students can ultimately envision themselves as future scientists.

Earth Educators’ Rendezvous

Last month, I attended the Earth Educators’ Rendezvous in Albuquerque where I participated in the Geoscience Education Research and Practice Forum. Approximately 40 geoscience educators and researchers gathered for four days to prioritize grand challenges in geoscience education research and recommend strategies for addressing the priorities.

Both in small working groups and large group feedback forums, we discussed research on students’ understanding in geology, and environmental, ocean, atmospheric, and climate science; research on K-12 teacher education; Earth and societal problems; access to underrepresented groups; cognitive science unique to geoscience (e.g., quantitative reasoning, temporal reasoning, spatial reasoning); instructional strategies to improve learning; and research on institutional change.

In the evenings to clear my mind, I took to the hills—literally—and was amazed by the local geologic landforms!

Amy Pallant at Kasha-Katuwe Tent Rocks National Monument. The cone-shaped tent rock formations are the products of volcanic eruptions that occurred 6 to 7 million years ago and left pumice, ash, and tuff deposits over 1000 feet thick.

Basalt cobbles at Petroglyphs National Monument created by a lava flow around a hill (that has since eroded).

Back at the meeting, I was in the working group focused on research on instructional strategies to improve geoscience learning in different settings and with various technologies. Because this topic is so broad, developing a list of grand challenges brought up a wide range of ideas. In the end, we narrowed our list to six grand challenges and began to outline strategies to address them.

The ideas developed will be presented at AGU and AGI this fall, and members of each group will be writing white papers. I’m hopeful that the product of this work will be like the influential Earth and Mind II, with the geoscience education research field and educators benefiting similarly.

The Earth Educators’ Rendezvous and the nearby landscapes were both inspiring. No wonder they call New Mexico the land of enchantment.

Chad’s Great American Eclipse Chase: Part 11—Returning home, and recalling

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.

The final leg of the trip is here at last. Beginning the last push back from Scranton, it seems we can feel life already drifting downward, returning to the quotidian from its brief perch among the cosmic reaches of the Sun and Moon’s conjunction. We can’t help but remember the moments over again, though. Transient as it may be, totality sticks with you, and we recall once more the rush of excitement as the shadow swept across and the mysterious beauty shone out. This video of our reactions as totality began—and receded far too quickly—captures the ebullience and awe in a way that no words ever could:

Yes – it’s really that exciting—for anyone and everyone.

So, as we find our eclipse reunion attendees once again scattering to the winds and find ourselves now driving along familiar roads toward home, we can’t help but smile inwardly ever so slightly.

Group pic eclipse chasers

Our eclipse-chasing group takes one last reunion pic before heading our separate ways…until the next one!

Because even as friendships fall back into comfortable step and familiar surroundings rise up to greet us, waiting and unchanged, we know that we may be back among it all, but are simply not quite the same ourselves. Once you’ve experienced a total solar eclipse, you’ve gained a new perspective on the universe, a more humble take on humanity, and a renewed sense of connection to both. Though it always sounds sappy, the truth is that feelings of such depth are common and understood among eclipse watchers. Another thing that is shared? The impulse to do as our group did immediately after this eclipse ended—pull out the maps and charts and study the slate of upcoming eclipses around the world. Where next? A cruise ship off Chile in 2019? A visit to the plains of Patagonia in 2020? And of course the Great American eclipse redux in 2024, for which we’re already studying locations and weather maps…

Recognizing that it’s almost futile to try to bring the essence across, I urge you instead to check out this great piece from Vox, especially the video linked below. These interviews of some of the world’s top eclipse chasers represent an attempt to capture some portion of the ineffable something that drives them all forward. Better than any others I’ve found, their words capture the sense of why we all headed on the road this August 2017—and why anyone who made it successfully to totality this week can’t help but dream of their next opportunity to stand under the shadow of the moon.

VOX eclipse chasing piece background image

 

Chad’s Great American Eclipse Chase: Part 10—The road home – Pondering the details

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.

Sigh. The drive back. Just like the partial phases of the eclipse itself, everything passes by in reverse, but it’s never quite as exciting. Still, as we drive back we’re running into fellow eclipse travelers from across the country everywhere we stop and stay, and it’s clear that memories and thoughts of the eclipse remain top of mind for everyone. The kids have gotten in the habit of looking out the window first thing in the morning to inspect for clouds and looking at the sky at 1:27 every afternoon to judge whether clouds would have blocked the sun, had things happened that day. I share in the wonder, too, catching myself seeing eclipses in the sky ahead as I drive. I also find myself pondering a number of aspects of this particular eclipse and wondering about the questions they raise.

“Not quite night”

Difference between 1991 and 2017

The difference in the size of the Moon’s shadow as it passed over us during the 1991 eclipse (black circle) and the 2017 eclipse (white oval) is striking.

This eclipse was interesting in the way the light of totality felt — we definitely noticed during the eclipse itself that it definitely didn’t look like night, and didn’t really even look like a weird twilight, the way the 1991 Baja eclipse had. It turns out that there is a very understandable explanation for this. The Baja eclipse was very distinctive in that many factors lined up to make it one of the longest eclipses in the century. This meant that the dark part of the moon’s shadow, the umbra, was extremely large.

At the point where we stood in Baja, the umbra for the 1991 eclipse was 257 km wide. In comparison, the umbra over Gallatin was only 115 km wide. As a result, the lit portions of the Earth were much closer during totality, and the darkness was more muted. We weren’t on a point where we could see the horizon, but had we been, the effect of the 360º “sunset” on the horizon would have been much brighter than the one we saw in Baja.

Stunning rush of darkness

This is one I’ve been puzzling out ever since the moments following totality. The way in which darkness overtook us during this eclipse was very striking. Whereas we recall the darkness descending during the 1991 eclipse, our memory of the transition from day to dusky totality was of a more gradual phenomenon. In contrast, the darkness of this eclipse surged in almost violently. You can see this somewhat in the shadow bands video in the previous post; the fall of darkness and the degree to which it took us all by surprise is evident in the light in the video and in the change in reactions of everyone in the final seconds of the video.

I’ve spent considerable time looking into this question and am just beginning to puzzle out an answer. I thought it might be obvious, as the two eclipses were so different in so many ways. However, the most obvious factor, the speed of the moon’s shadow (also known as umbral velocity) was almost identical between the two events. Where we stood in Baja, the shadow overtook us at 1407 mph (0.629 km/s), while in Gallatin, the umbra hit us traveling at almost the same rate: 1447 mph (0.647 km/s).

The factors that go into this speed at any point on Earth’s surface are very interesting — ultimately, it breaks down into a race between the speed of the moon and the linear speed of the Earth at the particular point of observation. Because the Moon orbits the Earth from east to west at a velocity of about 1 km/s, its shadow travels at the same rate. The linear speed of Earth’s rotation is about 0.5 km/s at the equator, and less at higher and lower latitudes, so the shadow always travels from west to east, and does so most slowly when falling on the equator. This is a complicated brew, of course, and the calculation of umbral velocity is an active area of discussion. It is also all mixed in with additional considerations of geometry—the shadow falls obliquely as it first meets Earth and again as it exits, and thus travels much more quickly at those points. (At first landfall in Oregon on Monday, for example, the moon’s shadow was traveling 2416 mph (1.080 km/s), almost twice the rate it swept across us in Gallatin.)

Concorde and eclipse

An amazing image of the Concorde during the 1973 eclipse over Africa

For eclipse chasers, of course, this all provides a bit of a recipe for finding the longest totality. As with our experience in Baja, finding a point where your speed is as fast as possible relative to the shadow’s is essential. For most of us, this means finding a point near to the equator. But there are other ways to do it—in a now-legendary (and perhaps never to be repeated) story from in 1973, a group of eclipse chasers did the ultimate, commandeering a prototype of the Concorde and chasing the moon’s shadow across most of Africa at above the speed of sound. This amazing feat, which resulted in a mind-blowing 74-minute experience of totality, was captured in a short and fascinating French-language documentary clip. This is the stuff that eclipse chasers can only dream of, despite their attempts to do similar things. It makes for some legendary images as well.

The cool thing about this eclipse was that there were so many observers, which permitted many things that have rarely been possible otherwise. Some of the observers were in space, which made for some amazing shots, including this one from NASA, in which you can see the shadow pass across the whole US.

The moon's shadow as seen from space on Aug. 21 (Credit: NASA)

The moon’s shadow as seen from space on Aug. 21 (Credit: NASA)

If the difference in rate we perceived is because of something other than mere perception and psychology (indeed, those may turn out to be the crowning aspects overall), it’s definitely more complicated. Two possible other factors that could be at play are the difference in our location relative to the centerline between the two eclipses and the effect of the Moon’s apparent size relative to the Sun. Some of this boils down to surprisingly arcane geometry, and I’m still working both of these ideas through somewhat—stay tuned for more thoughts in an epilogue post!

Coronal predictions are improving

One interesting thing about this eclipse was the fact that there were some notable coronal predictions ahead of time, and they were generally fairly good. Check out the comparison between the latest prediction before the 21st and the corona itself. Not too shabby—the similarities are definitely there…

Prediction of the Sun's corona during the Aug. 21 eclipse

Predictive Science’s prediction of the Sun’s corona during the Aug. 21 eclipse

Mark Rosengarten eclipse image

Mark Rosengarten’s stunning image of the Aug. 21 eclipse

 

Not-prominent prominences

Solar flares Aug. 2017

An amazing capture of the solar flares during the Aug. 2017 eclipse. (Credit—Flickr: moshen)

One other thing that was quite notable about this eclipse was the fact that there were prominences, but that they weren’t readily apparent to the naked eye. At very first glance, I thought I saw a very apparent prominence, but I was mistaken—the perception of the eclipse with the naked eye was primarily one of black disc and feathery corona. However, through binoculars or a telescope, a number of prominences were quite visible, including many in a closely connected line along the sun’s perimeter.

Sunspots during partial phases

Sunspot group 2671 was clearly visible during the eclipse’s partial phases

Prominences are fascinating and complex, and are closely associated with sunspot activity among other things, and we had some interesting luck this year. Despite the fact that we’re very near the 11-year solar minimum of sunspot activity, a new sunspot group appeared just prior to the 21st—Sunspot 2671 came into view on Aug. 14 and the 27-day rotation period of the Sun made it move into just the right position that we were able to see it during the partial phases of this eclipse.

Tracking totality—in total

The flares and prominences, as well as the corona, change and evolve across the course of totality. These changes can be essential to understanding solar activity, but are generally almost impossible to observe during the fleeting moments of coverage. This eclipse was different, though. Citizen astronomers across the country banded together to form the Citizen Continental-America Telescopic Eclipse Experiment (CATE), in which they organized and crowd-sourced video from a series of carefully calibrated and positioned telescopes at 50-mile increments along the path of totality. While they will be assembling and studying the resulting video for years, the first cut was just released, and it’s amazing to see, even if grainy and in its first stages. More evidence as we continue our drive back north that this was truly an eclipse to remember.

2017 Totality movie – first cut

The initial cut of the Citizen CATE movie of the entirety of totality on Aug. 21, 2017

Chad’s Great American Eclipse Chase: Part 9—First impressions, and the experience of totality

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.

Wow. That’s pretty much all one can say after an event like that. Once an eclipse has passed, it’s hard to capture it in words. We’ve had almost a full day since the event, which ended up so filled with plenty of excitement and recounting of individual experiences that there was barely a second to log experiences in one way or another. We’re off to another day shortly, so I’m posting some main impressions here, and will return with a few more in-depth posts about the event, how it unfolded, and some musings on various details.

Partial phases and setup

The atmosphere here at the Fairvue Plantation was calm, but buzzing with activity. A band was scheduled to play for a viewing party across the eclipse timing, and people were busy gathering and setting up chairs and tables all over. In the end, there were surprisingly few people in attendance, but we were able to share the partial phases with many of them.

We set up telescopes to project the partial phases on a card so they could be easily seen by many. There were several sunspots visible on the face of the sun, and it was great to watch the sun’s disc be slowly eaten away by the moon. First contact, at 11:59 local time, started the excitement buzzing around the whole group. The remainder of the early partial phases went by slowly, with people watching the projection and trying to capture digiscoped images through the telescope we had set up for direct viewing.

Late partial phases, pinhole projections, and shadow bands!

Shadow bands

A screenshot from our video of shadow bands immediately before totality

During the later partial phases, about a half hour or so to totality, things really got going. The trees all aroundus projected readily visible images, patterning the sidewalk everywhere with miniature crescent suns. Guests arriving for the party or relocating from the special Eclipse Brunch were awestruck at the zoomed telescope views. We spent some of the time looking at the great DIY Sun Science app, developed by colleagues of our Sherry Hsi at the Lawrence Hall of Science, trying to decipher the various filtered views and predict what the Sun’s corona and prominences might look like when totality hit.

As the minutes moved on, the light became extremely eerie. We kept telling each other to stare at the ground, and marveled together at how weird things felt. The light seemed almost yellow, with the world feeling stripped somehow of its usual vitality. In the ten minutes or so prior to totality, we quickly grabbed a sheet from the cottage and extended it in the hope of perhaps seeing shadow bands. This was rewarded with one of the big successes of this particular eclipse — shadow bands were clearly visible across the length of the sheet, dancing quickly and then disappearing, then returning again. The video below  captures them if you squint carefully, though as we noted before, they’re particularly difficult to photograph. They returned once again in the moments just prior to totality, and then…

The Rush of Totality

…darkness was upon us! In a literal rush this time. In discussion afterward, it seemed to all of us that totality’s darkness moved in with an unexpected ferocity, catching us almost by surprise (more than almost, in my case, as you can see in the video above). Then, totality. And the screaming. And the staring. Oh, the staring – what an amazing sight. First impressions? The corona was compact, but had some large lobes in different places. Prominences were almost not visible at all initially, but were visible through the telescope, which I moved into place during the later phases of totality. A line of prominences was visible along about 1/4 of the disc, light red rather than the fiery red points of the 1991 eclipse we saw in Baja.

Diamond ring effect

A capture of the diamond ring, shot through our scope in Gallatin, TN

The darkness during totality was much less than in the 1991 eclipse — it was dark out (the automatic lights on the cottage turned on mid-way through!) but it didn’t feel or look like night time to me in particular. Instead, the total eclipse felt as if it were suspended in the sky during a dusky evening, like a pearl hanging above a dim landscape.

And then—it was over. Way faster than anyone expected, or certainly wanted. I had read reports from veteran chasers in the days prior stating that no matter what, it would feel like it was 8 seconds long. That was about exactly right—when we went around the group afterward, we pretty much all agreed that was how long it felt. This feeling of brevity shouldn’t have been surprising—after all, this was almost three times shorter than our experience in Baja—but it was still just way, way, way too short.

But exciting. Oh, exciting. The joy of seeing totality is hard to match or better, but in this case, I found a way, by being able to share it with the next generation. I’ll write more in a more comprehensive post soon, but nothing I write can capture the unbridled feeling of totality as well as the emotional reactions and almost primal disbelief of those experiencing it. Still to come: video of our group experiencing totality…

 

Chad’s Great American Eclipse Chase: Part 8—Prepping 101—Planning and prioritizing for totality

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

Eclipse viewed through a kitchen colander

Looking for an interesting and safe way to view today’s eclipse? Try pulling a colander ouf of your kitchen cabinet! (Photo: John Lord)

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.

Eclipse shadow bands

Shadow bands as observed during an eclipse in 2001

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.

NBC Heroes logo

Fans of the NBC series Heroes may be familiar with the diamond ring and Baily’s Beads depicted in its logo.

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!

Solar flare prominence

A burst of solar material leaps off the left side of the sun in what’s known as a prominence eruption. This image combines three images from NASA’s Solar Dynamics Observatory captured on May 3, 2013, at 1:45 pm EDT, just as an M-class solar flare from the same region was subsiding. The images include light from the 131, 171 and 304 Angstrom wavelengths. (Credit: NASA/Goddard/SDO)

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 collossal 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 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 tostand 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.

1991 eclipse

The amazing corona and evident prominences of the 1991 eclipse, as captured in a composite image by Mark Ryan