Saturday, August 26, 2017

Total Eclipse of the Sun - Part 4

This post concludes my four part series about total eclipses of the Sun. Part 1 described my first total eclipse experience, part 2 gave advice for observing eclipses and described my second total eclipse, and part 3 gave details of my preparations for the 2017 total eclipse. They are not necessary reading but you may enjoy taking a look at them. I will describe my trip to Madras, Oregon and the activities and events leading up to totality and just after. Much of it should be of interest to physics and astronomy educators. If you are all about the totality, I understand. Just scroll down to the picture of the total eclipse. All pictures and video were taken by myself unless otherwise noted.
Having path of totality cross the campus ensures having a great summer! Climbing tower loomed over volunteer campsite
My wife and I started driving from Los Altos, California to Madras, Oregon, about 10:30 AM on Saturday. The rest of the staff and volunteers at the Lowell Eclipse Experience were arriving Friday and Saturday and I wanted to join them. We were met by Rich Krueger, a physics teacher at Flagstaff Arts and Leadership Academy, when we arrived at Madras High School. We quickly pitched our tent in the volunteer area and were asleep by 11:00 PM. I woke up just before sunrise and noticed an osprey nest in the climbing structure next to our campsite. I wondered if it was occupied. While observing sunrise from the bleachers, I heard the ospreys chicks start cheeping just as the sun struck their nest. The adults quickly flew off to find some fish. Watching the four adult ospreys try and keep the chicks satisfied with fish was one of the highlights of the trip. We noticed when they brought a larger fish back, they would eat the good parts first before giving it to the hungry chicks.

H-alpha could see through clouds but would corona shine through?
Shot through iPhone good enough to show facula and prominences
Sunday was spent setting up the booths and displays for the Lowell Eclipse Experience. There were vendor booths from Lowell Observatory and Madras High School. There were activity booths from Northern Arizona University and Lowell Observatory. There was a group with several types of solar telescopes including a calcium line filtered scope with video display. The Science Channel had a stage for broadcasting live and a booth for free photos that used a green screen to put you in the total eclipse. The auditorium was set up to host talks by the Lowell Observatory astronomers. I set up my h-alpha solar telescope on my tripod and a Skywatcher clock drive. The clock drive only works well if you polar align it. This is difficult in the daytime but I had read about a trick in Sky and Telescope. Open an astronomy app that displays the night sky, I use "Night Sky". Place the phone flat on top of the Skywatcher and adjust the azimuth and elevation until the south celestial pole is centered on the screen. This worked beautifully. I could leave the scope for over an hour and the sun would stay in the eyepiece. I spent most of the day showing mostly staff and volunteers the chromosphere of the Sun. There were some awesome prominences all around the Sun. One extended an unusually large distance from the Sun. Unfortunately, it dissipated before totality. Sunspots don't show well in an h-alpha telescope because they reside on the photosphere. The line of about 3 sunspots that showed in white-light filtered scopes were faint except for the umbra of the leading spot. That proved useful because it was about the diameter of the Earth, allowing me to put the other features in perspective for people. One feature that did stand out was the facula that appeared as a bright stripe over the region where the sunspots were located. Sunspots occur in regions where the solar magnetic field is stronger and inhibits convection. They are a little cooler, thus dimmer than the photospshere. The energy still has to reach the photosphere. A facula is the location where this energy escapes, making it a little brighter than the rest of the photosphere. Showing people this amazing view occupied me until dinner. I put the scope away because the view was deteriorating as the Sun got lower in the sky and it was clouding up.

The Sun showed another one of its tricks before sunset on Sunday
Me and Rich and the odd annular eclipse graphic on Lowell booth
People started showing up for the astronomer talks that started at 6:00 PM. I set up two demonstrations to coordinate with the Lowell activity booth. One was the spacetime simulator that I use to discuss gravity and General Relativity. I would go through the demos depicted in the viral video plus a couple of new ones. A group from SPS posted a video where they show tides and the Roche limit on this "rubber sheet" model. You toss a group of 4-5 marbles sideways so they orbit the central 2 kg mass that represents Jupiter. They stay in a cluster until they get close, simulating a comet. The curvature of spacetime noticeably increases as they approach Jupiter. The gradient in curvature causes the marbles to stretch out in a line. They get closer, break into individual marbles, and then collide with Jupiter. The point at which they break up is called the Roche limit. I then told the tale of comet Shoemaker-Levy 9. The other additional demo is the simulation of gravity waves. I allude to them earlier when we observe that an orbiting marble spirals into the central mass. This is due to rolling resistance of the marble on the spandex but is a nice analogy for gravity waves. I explain that this effect is not measurable for the Earth orbiting the Sun. That is a relief for those worried the Earth is spiraling into the Sun. I then mention it is measurable for two orbiting neutron stars and the Nobel Prize for physics was awarded to Hulse and Taylor in 1993 for the first measurement of the effect of gravity waves. I first saw gravity waves simulated on a spandex sheet on Steve Mould's video. He mounts 2 castor wheels to a board and then attaches the board to a drill. Place the wheels on the spandex and start the drill. The wheels represent the orbiting black holes. The gravity waves are only visible on a slo-mo video or under a strobe light. I did this demo for my students for the first time last May under a strobe light. The number of "whoas" I heard confirmed my opinion that this was a great demo. Rich brought a drill and generator so we could try it. I showed him how it worked as he took a slo-mo video with his phone. When he watched the video, he exclaimed a loud whoa, just as I expected. Rich was bothered by how the drill and board blocked the view of the orbiting black holes and the point where the gravity waves were emitted. He decided to crawl under the spandex and record a video. His next "whoa" was much louder. His video showed two bumps in the spandex and the waves, but no drill and board. Then we hit on a great idea. Why not have the drill under the spandex? We tried this and knew we had a winner. At the conclusion of my first demo, Rich crawled under the spandex as I instructed the crowd to record a slo-mo video with their phones. After a few seconds of recording, they shared their video with those around them. It was a spectacular conclusion to what I hoped would be a memorable experience. Here is what it looks like:

In between "shows" I would put one or two of the 2 kg masses on the spacetime simulator and let children play with the marbles. That proved to be very popular. Some of them could barely see over the edge but they were fascinated by watching the motion of the marbles. The parents took non-stop pictures. Many people recognized the spacetime simulator from the viral video but they did not recognize me. I told them I was the one in the video and a few people took selfies with me and one even asked for my autograph.

Water refracts light around the edge of the bucket, toward eyes of the observers
Refracted image of the sun was enough to start the cheeping of the osprey chicks
My other demo was a variation on a standard refraction demo. You attach a coin to the bottom of a opaque container. Have students look down on the coin, then move slowly back until the top edge of the container just blocks their view of the coin. Pour water into the container and the coin appears. Have students draw the light path from the coin to the eye for the empty container and the filled container. I decided to super-size this demo so it would work for a larger group. My intent was to make an analogy with the bending of light by refraction with the bending of light by gravity. If the Sun just barely covered a star, you would still see it because the Sun's gravity would bend the light from the star around its edge. The same thing happens at sunrise. The density gradient in the atmosphere bends the Sun's image around the limb of the Earth. When you first see the Sun, it is still below the horizon. In the refraction demo the edge of the container would represent the Sun and the coin would be the star. I thought this was a good analogy to make but was a little concerned that it was too forced. Then I saw this wonderful demo making the same refraction to gravity analogy by Paul Doherty from the Exploratorium. I new if Paul thought it was a good idea, then it really was! To super-size it I used a 5 gallon bucket. Instead of a coin, I wanted to use an LED light. I searched for "waterproof LED" and found many options. It turns out that putting LEDs in the vases of floral arrangements is a thing. I found some that were remote controlled and very bright. I epoxied a washer to the bottom of the light and placed a strong magnet underneath the bottom of the bucket. This prevents it from moving as you pour in the water. As it was getting dark I asked Rich's students from Flagstaff to gather around the bucket. I turned on the "star" and asked them to carefully move back until it was just blocked by the edge of the bucket. I explained the analogy and then started pouring in water. They got excited when the star came into view. I could even see the light hitting their eyes at the moment there was enough water in the bucket. I had a second light that was in the bucket with the water. That allowed me to just keep pouring the water back and forth for each demo. I did this demo a few more times for the people attending the event, then turned the buckets over to the high school students. They quickly mastered the demo, adding their own twists. They liked to ask the crowd to look at the bucket, then they said "imagine there is a star in the bottom" and at that point they would use the remote to turn it on. That got their attention as the bucket had a cool glow to it. Here is a short clip of them doing the demo as seen by an observer:

Rich Krueger's students show gravity bending light
The students also had some cool demos that they helped Rich build. They attached large fiber optic cables to spandex and put a mass on it. This warped the path of the fiber optic cables, showing what gravity does to light. It looked very dramatic at night when they were lit. The students had developed a great presentation. They concluded by showing if the object in the center was a black hole that light would not escape and could be made to orbit it. As I watched the students enthusiastically go through their "show", I thought about the tremendous influence of Paul Doherty who passed away just before the eclipse. Because of Paul I had decided to proceed with the bucket demo and here were some future scientists, engineers, and hopefully teachers, benefiting from his influence. The students had seen Paul's refraction analogy video and had prepared several wineglass bottoms so they could perform it themselves. This is just the tip of the iceberg of Paul's overall influence on every educator and science enthusiast who ever came in contact with Paul or one of his many demonstrations or online posts. The science and education community has lost a giant. However, Paul's influence will continue to resonate and impact many generations to come.

If you are interested in trying the bucket demo I suggest using metal buckets and paint them flat black inside and out so the entire bucket doesn't glow from the light. That will make the desired effect more apparent. Instead of a washer, epoxy a magnet to the light to attach it to the bottom of the bucket. I am sure Paul would have liked this one, I hope you and your students do too.

Rich Keuger takes the audience on a tour of the Universe
As the sky got darker it got cloudier, dampening prospects for the star party and causing anxiety about the next day's total eclipse of the Sun. The forecast predicted it would clear up after 9:00 PM. At about 9:10, half the sky had cleared and by 9:40 it was almost all clear. My faith in meteorologists and their forecasts was restored. Because of the clouds and distance from my van to the football field, I did not set up my 10" SCT. There were some telescopes set up but the main attraction was Rich's telescope connected to a large monitor. Rich would point out where an object was with a green laser pointer, then bring it into view on the screen. He could then describe the object and give details about it to the whole group. He kept a large audience spellbound well after I went to bed.

LGHS AP Physics and APES teachers prepare for totality
I woke up before dawn and watched to see if the osprey chicks started cheeping at sunrise again. They did right on cue. As the sun climbed higher, clouds of smoke became visible toward the southwest. They appeared to be slowly moving toward the region of sky where totality was to occur. As the morning went by, the smoke thinned and became less of an issue. The thin layer of cirrus was more of a concern. I set up the h-alpha again and showed the gathering crowd the chromosphere that would be visible to the naked eye in just a few hours. I was able to leave it tracking the Sun and do a few more shows with the spacetime simulator. The students did more shows and the bucket demo worked great in the daylight too. My sister and her husband arrived from Seattle. One of my colleagues was also there with her husband, 3-year-old son and father. I even ran into a former student who was excited to tell me about his summer internship at JPL. I was disappointed that they did not announce first contact on the PA system. I watched in my h-alpha and listened to the eclipse app someone nearby had countdown from 10. Right at zero I noticed a tiny indentation on the upper right corner. I waited and watched it slowly grow before I announced first contact. Soon after a few sharp-eyed observers could see it in their eclipse glasses. The eclipse I have been waiting for for two decades had begun! I brought out the pinhole picture box I made for the eclipse and it worked great. It shows the equation for General Relativity.
LGHS Teacher with Sun Funnel on 8/21, by R. Peters
In my third post in this series I mentioned using perf board for a pinhole picture. I found it was much easier to punch uniform holes into a piece of cardstock placed on thick cardboard. The pinhole images were crisp if the screen was about 20" from the pinholes. This is a little more than the length of a copy paper box. At this distance the pinhole images won't overlap if they are 4-5 mm apart. A colleague made a DIY video of my design if you want to make one for the next eclipse. They look cool even if there isn't an eclipse! I also mentioned using the Sun Funnel I built. I decided to leave that to my colleagues staying behind at Los Gatos High School. They would have 75% of the Sun covered during the morning tutorial. The big advantage of the Sun Funnel is that it allows many people to safely see the eclipse at once. They also had eclipse glasses and pinhole viewers. My awesome substitute teacher helped with the observing and then streamed totality from Madras on the Exploratorium website, just like my sub did in 1998.

My only good total eclipse picture was still very satisfying
I felt dorky taking a selfie with the eclipsed Sun and the picture captured the feeling
I went to great trouble to bring the large convex mirror I made using a kiddie pool and a spaceblanket that I described in previous posts. When it came time to deploy it, I decided to leave it in the van. All it would show is an all-sky view of the ominous clouds and threatening plumes of wildfire smoke. I also worried it would be a trip hazard. Maybe my next eclipse. I set up my video camera on a tripod and zoomed in on the Sun. I also pointed my GoPro so it would capture some of the crowd and the eclipsed Sun. People were still using my h-alpha to view the partial phase as the clock on the football scoreboard counted down the last minutes before totality. I left it on the tripod and hand-held my camera with the 300 mm telephoto lens. I knew this would smear out the longer exposures but taking pictures wasn't my priority. Time seemed to speed up as the clock counted down. I forgot to ready my binoculars but didn't even realize that until I saw them on the ground after totality. Shadows got sharp, the air cooled, the sunlight seemed to drain from the sky. People were EXCITED! This was really happening. Just before second contact I noticed the contrail of a jet heading toward the Sun. Because the contrail might interfere, I joked that you never have a surface to air missile when you need one. My brother-in-law heard me and took his eclipse glasses off to see the jet. He accidentally got a good look at the slender crescent. We were worried but he seemed fine later. The Science Channel counted down the final 10 seconds over the PA and then BAM, totality. I have seen it before but will never get used to the sight. It looks so wrong and yet so beautiful. I tried tracing the three coronal streamers out as far as I could and looked for structure in the corona close in to the Sun. Coronal structure detail was slightly obscured by the thin cirrus that had plagued us all morning. I don't think anyone witnessing their first eclipse noticed, and if they did, they wouldn't have cared. It was the same amazing life-changing sight I have seen before, and yet was completely unique. I took a quick selfie with my iPhone, then pressed the shutter on my camera and waited for the five bracketed exposures to complete. I looked up at the scoreboard clock and saw only one minute had passed. It seemed like a long time. Now it was prominence time. I saw two very bright ones that revealed their pinkish-red color with averted vision. I was studying these beauties and heard what might have been a warning to prepare for third contact. Before I knew what was happening, there was the diamond ring. I think the countdown clock still had a few seconds on it. Those lunar valleys can be tricky. Some people put their eclipse glasses back on, others just stood there smiling and looking emotionally exhausted. Those that just witnessed their first total eclipse felt compelled to say how unbelievable the sight was. They felt unprepared for what they saw, verifying my belief that there is no way to prepare for this experience. Some had tear tracks down their faces. Before the path of totality swept off the Earth's surface it will have deeply affected millions of people, leaving them with a sense of awe that will not go away.
  Totality starts about 1 min in, focus goes out of whack later but the sound is good!
GoPro of totality with Rush soundtrack. Look for eclipse chasing plane toward lower right.

Sister Colleen, me, and wife Gia, photo by Science Channel
Some people left right away while others stayed for fourth contact and the astronomer talks in the theater. I stayed by my h-alpha and many people stopped by to have a look. They now knew what a prominence really looked like and appreciated being able to see them again. After fourth contact I started packing up. We were ready to leave by about 1:30. We got texts from people reporting heavy traffic but my iPhone traffic map showed it dissipated around Bend with a few slow spots after that. It didn't look like I needed to take my backup route, cutting east over to 395. We headed out, taking a few shortcuts but sticking to 97. That turned out to be a mistake. Something went very wrong in the small town of Chemult about 100 miles south of Madras on 97. Traffic backed up solid from La Pine to Chemult. It took us 10 hours to go about 100 miles. After Chemult there was no traffic but it was getting late. People were pulled over at every turnout, sleeping in their cars. There were no motel vacancies. I was feeling a little tired but considered driving all night. I then realized that would have us arriving in the Bay Area at the peak of rush hour. That would have driven me insane so we found a side road and pulled over for a four-hour nap. Other than the cat that jumped up to sleep on the warm hood of our van, things went smoothly the rest of the way home. When people asked what time we got home, I answered "one hour after totality ended, but on Tuesday!" I have tried finding out what happened in Chemult to no avail. However, I think I know. We have done this drive many times to go skiing at Mt. Bachelor. Chemult is the last chance for gas for many miles while driving south on 97. I think a lot of people stopped at the last gas station and it backed up onto the road. People trying to get back on 97 stopped traffic too. When we drove through Chemult there were a lot of cars at the gas station. The police had coned off the right lane, forcing us to drive in the center turn lane. They would stop traffic going south to let cars back on 97 from the gas station. I think we saw the remnants of what must have been quite a scene. I wonder if the gas station ran out of gas at some point too. I will probably never know for sure but we were both fine with what happened. I had our best substitute teacher for Tuesday and my wife was able to do some business on the road with her phone Tuesday morning. I have often driven that road when there is solid ice, that is worse. I now don't trust the travel time estimates given by my iPhone. During the 11 hours of crawling on 97 it kept saying we were just 8 more hours from home. Had I had better information I would have used my backup route.

I have been looking forward to the 2017 Great American Eclipse for about two decades. Now that it is over I feel a little letdown. The surest cure for post-totality blues is to start planning the next trip to the Moon's umbra. You will probably find me on a cruise ship off the west coast of Mexico in 2024. The 2028 total eclipse in Australia looks good too, I better take care of myself! Although seeing a total eclipse of the Sun is an incredible experience, there are other spectacles of nature that are equally beautiful and inspiring. Seeing an erupting volcano or an aurora come to mind. Perhaps these don't get the same attention because theoretically you can go and see them almost anytime you want, if you can afford it. There seems to be a premium for natural phenomena that are rare. I wonder how people in the future will think of total eclipses when they can board a rocket and travel to the Moon's umbra anytime they want for as long as they want. I believe one of the greatest natural displays, sunsets, are underappreciated because they are ubiquitous. I am glad we don't have to wait years to see one. Usually, all you have to do is take a walk outside and look up.

Sunset, August 20, 2017. If this was rare, I would have a t-shirt saying "I Saw the Great American Sunset in Madras, 2017"

In Memorium: Paul Doherty

One of my personal mentors was a very down-to-earth Physics celebrity, Dr. Paul Doherty of the Exploratorium. I met Paul within a month of my first year of teaching as part of the New Teacher Institute so he has been a major influence on me. Paul passed after a battle with cancer last week. Despite knowing his time was near, like many I was wrecked at the news. We had all secretly hoped that he would make it to see another solar eclipse but it was not to be. During the eclipse I thought of Paul and the sheer joy he had at experiencing such beauty in science and nature.

Every teacher that has been a part of the Summer Teacher Institute, New Teacher Institute, conference or public outreach at the Exploratorium knew Paul. This was not just because he was a memorable guy, although he certainly was, but because he always tried to get to know everyone. His enthusiasm and curiosity were as infectious as his smile. He seemed to know everything, able to speak on anything related to Physics, and most things in other fields of science. Once while watching the credits of a science documentary I saw "Thanks to Paul Doherty, Science Historical Consultant," and when I asked him about it he said, "Yeah I was just helping them out." He's written books and papers, developed exhibits and more demonstrations and educational activities than you can count. When Paul developed an activity it was hands on, used easy to access materials, and most importantly for teachers, worked every time. He enjoyed playing the whirly, playing with flashlights and was an Iron Science Teacher champion.

Paul made the intricacies of the world easy to understand; he could answer complex questions with a pencil or a telephone cord. He absolutely delighted in every question that was asked of him and he had a few common responses:

"I don't know, let's try it!"
"Well ... it's more complicated than that."
"What do you think?" 

He was the smartest man I have ever known and he was perfectly comfortable saying "I don't know." The power in that was palpable. When I asked him a question and he countered with asking me my opinion I no longer felt ashamed at not knowing but excited at the prospect of figuring it out on my own with Paul as a guide. I can say for certain that knowing Paul made me a better teacher because he was an amazing teacher. They say a teacher's influence is hard to measure and I would argue that Paul's reach is truly immeasurable. He helped hundreds of teachers who in turn have each taught or will continue to teach thousands.

Julie Yu of the Exploratorium put together this video of Paul from an interview for the museum. It both warms my heart and saddens me to see Paul speak again. Every response is very quintessential "Paul." I may watch it when I need to remember why I teach, or just when I miss him.

Paul's family has set up a page for sharing stories and thoughts of Paul. If you knew him I encourage you to leave a response. Some of what I wrote about Paul is below:

"...the most important things I learned from you was to keep the wonder, to not be afraid of not knowing to be fascinated with learning and to forever be curious. Over a year ago you wisely responded to a teacher's question with "The best gift  for a physics professor is a puzzle they don't don't understand." You encouraged me to delve deeper, gave me permission to have fun and will forever be an inspiration."

May we all teach as Paul did: with enthusiasm, wonder and a true passion for science education. 

Thursday, August 10, 2017

A Trap for Theorists

EBIT Cutaway
One of the highlights of the workshop program I conduct at Lawrence Livermore National Laboratory is a tour of the Electron Beam Ion Trap or EBIT. In about an hour Dr. Greg Brown explains how this incredible instrument works and what it is used for. I have toured it many times and learn new things on each tour. Before I started working at LLNL, I had no idea what an EBIT was. Now I know it is essential for many important areas of physics and astrophysics. The physics behind how the EBIT works covers many topics encountered in an introductory physics class. The areas of physics and astrophysics it is used for are highly interesting to introductory physics students. Because of this I decided to write a post about EBIT.

Astrophysics was enabled by the invention of the spectrometer. However, it didn't get started until the connection was made between the odd lines observed in solar and stellar spectra and laboratory measurements of the spectra of elements. Many scientists and engineers contributed to this effort but Gustav Kirchoff and Robert Bunsen get the lion's share of credit for this accomplishment. Together they developed techniques to purify samples and observe and record their characteristic spectra in the uncontaminated flames of, you guessed it, a Bunsen burner. This work allowed them to discover several new elements. More importantly, they realized that their work could be used to decipher the information coming from the universe through a spectroscope connected to a telescope. By comparing the absorption and emission lines of astrophysical objects to the lines measured in the lab, astrophysicists could determine the composition, temperature, magnetic field strength, motion, and much more about astrophysical objects. This led to an explosion of discovery that resulted in humans learning about nucleosynthesis and the Big Bang.
By Poul la Cour & Jacob Appel - Historisk Fysik bind I,
Bare Uranium Spectrum by EBIT
The modern day Kirchoffs and Bunsens are working at EBIT. They use a high energy beam of electrons to create ions and hold them still. They use advanced spectrometers to measure the spectral lines of these ions. You might wonder why this still needs to be done. Haven't we already measured all the spectra of the elements? The answer is no because the spectra are different for different ions and isotopes of the same element. When you consider all the naturally occurring elements and all of their isotopes and possible ionization states, you realize that this is a herculean task. Another reason this wasn't done a long time ago is that it is extremely difficult to create some of these ions. Imagine the energy required to remove the 92nd electron from a uranium atom. That is something they have done at EBIT. These high ionization states are found in high energy environments like the accretion disks of black holes, supernova, fusion experiments, and x-ray lasers. Without EBIT and other similar research facilities, astrophysicists and fusion scientists would not be able to decipher the observations they make with their spectrometers.

We arrived a little early at EBIT for this summer's tour. Luckily, we were met by a high school physics teacher from Hawaii, Tessie Lumabao. She had completed Level 1 and 2 of the Fusion/Astrophysics Teacher Research Academy in 2016. Tessie had first seen EBIT on the TRA tour I took the teachers on last summer. Now she was working there as a summer intern. One of the primary benefits of the TRA program is the opportunity for a paid research internship at LLNL. Tessie introduced herself to this year's TRA participants and excitedly described what she was working on. I asked her to elaborate when she mentioned they were observing the spectrum of "neon-like molybdenum". She explained that it was a molybdenum atom that had 32 electrons removed by EBIT's electron beam. That left it with only 10 electrons, just like a neutral neon atom. At this point Dr. Greg Brown joined our group and started our tour. Tessie's brief talk proved helpful as Dr. Brown scattered things like "helium-like uranium" and "beryllium-like iron" in his remarks throughout the tour. We still saw a lot of Tessie as she dashed back and forth between computer monitors connected to EBIT and the spectrometers as they collected data.

The experiment that was being conducted with Tessie's help has important implications for one of the foundations of modern physics, quantum electrodynamics or QED. This theory explains how light interacts with electrons. In other words, it explains everything you have ever seen or ever will see. QED has been tested extensively and has held up very well. It is considered to be the most accurately tested theory in physics. Theorists can use it to predict what the spectral lines of a given ion will be. These are extremely complex calculations and need to be tested with something like EBIT. In many tests their predictions hold up. In some there is a troubling discrepancy. The question is, who is right, the theorists or the experimentalists?  Observations of the spectra of astrophysical objects suggest it is the experimentalists using EBIT that are correct and the theorists and possibly QED that have a problem. It struck me that we were visiting a research facility that could change a fundamental theory in physics and one of our TRA high school physics teachers was participating in this endeavor.

Dr. Elmar Trabert
I wanted to learn more about this area of research and did some digging after the workshop was over. The LLNL EBIT website is very helpful but hasn't been updated recently. Searching online I found a remarkable paper by Elmar Trabert in the journal Atoms called "Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter's View" (note: clicking on preceding link will download the pdf file of this paper). This 70 page paper was outside the realm of my usual summer reading but the introduction drew me in and I spent a lot of time reading the parts that I found interesting (and understandable!). I will share a few items here. The page numbers I refer to are the ones in the document that start on page 15. Here is what caught my attention in the introduction on page 15:

"Burkhard Fricke... recalls advice by his elders as “If theory and experiment disagree, work on theory; if they agree, improve the experiment.” Alan Hibbert... would add a caution to this: “If theory and experiment agree, be aware of the possibility that both may be wrong.” Right. Moreover, if one considers another research practicality, one may suffer the consequences “if theory and experiment agree, you won’t get funding for further research.” "

This didn't sound like a typical research paper. It had a sense of history and humor. He continues in the introduction on page 16 to say this:

"My aim in this article is a discussion of what I as an experimenter expect from theory and atomic structure computations, how I try to assess the quality of the work, and what experiment can or can’t do towards a critical validation process of such calculations. After all, experiments and experimenters come in many flavors, too. We all make mistakes, and maybe we can learn from some of them that we have recognized by now. In this context, I dare to digress into anecdotal evidence of various problems in the interplay of atomic structure theory and experiment, into human and technical sources of error and uncertainty, before turning to a more systematic discussion of data on specific isoelectronic sequences. However, I will not present an ultimate recipe for assessing calculated data. Both, experiment and theory, are intertwined in the scientific process, and progress may involve a new perspective, if not always a paradigm shift."

I found a mention of the QED vs experiment issue on page 52:

Dr. Greg Brown
"Since neither experimenters nor theoreticians found fault with their own ways and results, the systematic discrepancy between experimental and computed line ratios was blamed on a variety of collisional-radiative processes in distant light sources that one could diagnose by the size of the discrepancy. However, Greg Brown’s extensive and tedious systematic studies at the LLNL EBIT [183,184] agreed with the stars, but could not suffer from the same collisional effects."

I chuckled at the adjective "tedious" but I am sure the importance of the measurements masked any sense of drudgery that may have been present during this work at EBIT. Following this mention of Dr. Brown's work, Trabert begins another digression that is uncharacteristic of the typical academic journal article. I found it fascinating. It starts on page 53 and I will leave it to you to download this paper and read this short passage on your own. If you are like me, you will get drawn in and spend more time scrolling through the rest of the paper for more of Trabert's wit and wisdom.

Another critical task of EBIT is to help test and design advanced spectrometers. On the tour we got to see and hear about what Dr. Brown described as the most accurate and sensitive spectrometer in the world. It is of a type I had not heard of before touring EBIT, a calorimeter spectrometer. Instead of using a grating and charge-coupled device (CCD) to measure the energy of incoming photons, it uses the temperature change photons cause when they strike the detector. EBIT helped design the x-ray calorimeter spectrometer that flew on the ill-fated Suzaku and Hitomi x-ray observatories. Suzaku lost its cryogenic coolant in just a few weeks due to a malfunction. This Japanese Hitomi spacecraft went into an uncontrolled tumble soon after it went operational and spun so fast the solar panels broke apart. Prior to that, it demonstrated the remarkable capability of the calorimeter spectrometer for x-ray astronomy. This will undoubtedly result in a follow up mission in the future.

What an incredible opportunity Tessie and other teachers have to work in a facility that is helping to design and test instruments that will fly in space and discover new wonders about the universe. If you share this opinion, I urge you to sign up for the Fusion/Astrophysics Teacher Research Academy next summer at LLNL in Livermore, CA. It is tentatively set for the last two weeks in June. We typically have teachers from the Bay Area and Central Valley attend, but some teachers have traveled from as far as Thailand and Hawaii for this opportunity. I will post on The Blog of Phyz and on my Twitter account, @kilroi22, when registration opens. If you are wondering what it would look like to see an object that is so energetic it has atoms like iron missing most of their electrons you are in luck. Make your way to the eclipse path on August 21st. The solar corona is like a giant EBIT!

Tuesday, August 08, 2017

How a VCR works—I had no idea

I know. I didn't think I needed to know, either. But I was wrong.

We've all used them, and we likely have a rough idea of what's going on in there. But I didn't know most of this, and confess embarrassment at the depth of my VHS ignorance.

The challenge, history, and inner workings are surprisingly enthralling. It's 18 minutes that you won't regret. Trust me on this.

The Impossible Feat inside Your VCR

These days a VCR seems more quaint than anything else. But in fact, there's a device inside every VCR that solved what seemed to be an unsolvable problem. The video head drum is a fascinating solution to the complex problem of tape speed, and therefore I think it deserves to be remembered. Plus, the video head drum shares some motor technologies with modern hard disk drives. So there's that.

Monday, August 07, 2017

Where we are with California NGSS state tests

This post is really just a link share. I don't know about you, but I often get so wrapped up in teaching physics that I lose track of where the state is in terms of mandated statewide assessments.

Gone is STAR and its CSTs. In development is the California Science Test (CAST), part of the California Assessment of Student Performance and Progress (CAASPP) [No program is legit unless it has a handy acronym or initialism.] So CAST is the product of CAASPP Science.

The skinny: The CAST is for eligible students in grades five, eight, and once in high school. It's currently in development with pilot tests being run. The test will become operational in the 2018-19 academic year.

Here's the California Department of Education's CAST web page.

Here's a link to released practice test items. When I looked, I was disappointed. Perhaps material for a post to follow. Take a look for yourself at Online Practice and Training Tests Portal.

And here's the promotional video offered on that page.

Which cup fills up first?

Depending on your social media foot print you may have seen a lot of this image over the last few days:

If you didn't achieve "genius" status the first (or second) time you looked at it, that's ok. It is a bit tricky and I don't think solving this has a direct correlation to your IQ. To be honest, I missed the closed pipes the first time I looked at it too. Some people got really upset with others over this thing. Massive debates were sparked and it was determined "Well, we just can't be sure, without doing it." Hands on experimentation to the rescue!

A facebook page called Prozix made a 3D print of this now infamous brain teaser and did the actual experiment. Now you can confidently tell your students the answer when they try to stump you. Video of the experiment is available here (or here) but make sure you try to make your own guess before viewing.

Sunday, August 06, 2017

Vector Birthdays

I will be teaching AP Physics C, Mechanics and Electricity & Magnetism, for the first time this year. Although I have been graciously gifted curriculum from several veteran teachers, you have to make your curriculum your own. So I'm tweaking what I have, splicing and dicing things together into what I think will make a good learning experience for my students. (Of course you know I'll have to rewrite it next year once I actually know what I'm doing).

One of the things I wanted my students to practice was drawing vectors. I found a lot of worksheets online but wanted something a little more open. Adding to my complicated needs is the upcoming eclipse and my plans to travel to Oregon like Dan. I need four days of sub plans right at the beginning of the year. At last I had an epiphany:

The instructions should be simple enough for students to do without help from the sub. Each student (unless they are twins) will have an entirely different vector drawing. Its a quick and easy way to practice. Below is the example I'll have the sub project:
I can ask students who has the smallest resultant, the largest or perhaps the one closest to 90 degrees. This use of child-specific numbers make me think how else I can use them. Perhaps problems with blanks students fill in with numbers only the know: their birthdays, their address, their phone number. Everyone gets to practice the same process but each problem would be unique.