Monday, June 19, 2017

Total Eclipse of the Sun Part 2

I won't have to worry about changing film for 2017 eclipse
In my last post, I shared my first total eclipse of the Sun. I hoped to spur into action people who were on the fence about going. Hopefully you have started investigating the logistics about how to place yourself under the path of totality on August 21st. In this post, I will share my advice for making the most out of the experience and my 1998 trip to Aruba to witness my second total eclipse. I am in no way an experienced eclipse chaser or an expert on eclipse observation and photography. My hope is to motivate you to do further research into the various aspects of total eclipse viewing that I will raise. All of the pictures and video in this post were taken by myself in Aruba.

There are several considerations for selecting your observation spot. For me, the most important is the prospect for clear weather. When looking at various choices available to you, compare the probability for clear skies for the day and time of the eclipse. Another important factor is the length of the eclipse, but for me that is secondary. A total eclipse is one of those experiences for which the perception of the passage of time is highly altered. I was lucky to see one of the longest eclipses, 7 minutes of totality in 1991. The eclipse in Aruba was about half that duration at my location. Both seemed to last the same amount of time. I would select a location based on weather and then get close to the center line to maximize the duration. That is why you will find me in Madras, Oregon (2:00 min totality) on August 21st instead of Nashville, Tennessee (2:40 min totality). Do some research, there are many online sources for eclipse weather information. This chart shows the average cloud cover across the eclipse path.

If you are planning on photographing the total eclipse, my advice is do what I say, not what I did. I spent too much time fooling with my equipment in both of the eclipses I observed. For August 21st, I plan to snap a few pictures through my 80 mm refractor. I will not try and capture all the various phenomena associated with totality like Bailey’s Beads, the Diamond Ring, prominences, and the extent of the corona. My goal will be to have a nice personal souvenir, not to try and compete with the more experienced, skilled, and equipped eclipse photographers. They will share their results online. You can increase your chances of getting a good photograph by practicing on the Moon when it is near full. This will give you a good idea of what exposure to use and how large the image will be for your optics. I also plan on setting up my video camera to record the crowd, sky, and sound during the eclipse like I did in Aruba. I will not need to monitor it during totality. This will free me to observe as much of totality as possible using just my eyes and my 10 x 30 image stabilized Canon binoculars.

Observing a total eclipse without a solar filter is completely safe. It is the partial eclipse phase on either end of totality that is risky. It is not safe to look at any part of the Sun's surface (photosphere) for more than an instant. We have a natural instinct that prevents us from doing this. However, if you were determined to blind yourself, you could do it on any sunny day. What makes a partial eclipse a problem is our instinct is overridden by our curiosity. Furthermore, when it is a very thin crescent, the lower brightness can allow a person to look long enough to cause damage before wanting to look away. You won't notice the damage as it occurs, the eye does not feel pain. That is why it is important to have a variety of safe ways available to view the partial eclipse. Pinhole viewers, eclipse glasses, supervised telescopes/binoculars with solar filters firmly attached over the objective, and supervised telescopes/binoculars projecting images on screens are all good choices. A Sunspotter is one of the best tools if you have $430 to spend.

If you are lucky enough to be in the path of totality, you can look directly at the totally eclipsed Sun. You are now viewing the corona and chromosphere which are similar in brightness to a full moon. It is stunning to see in a telescope or binoculars but if you are looking when the eclipse ends, you will most likely damage your eye. It is important to know the duration of the eclipse at your location and stop looking about 30 seconds before it is predicted to end.

Just before the total eclipse and immediately after, there are two phenomena known as Baily’s Beads and the Diamond Ring. These occur when the only part of the photosphere that is visible is seen through valleys on the limb of the Moon. Baily’s Beads occurs when there is a crescent of valleys that the photosphere is peaking through. The Diamond Ring occurs when there is one last piece of photosphere visible. It forms the diamond and the corona forms the ring. Although many people have done it, including myself, it is not safe to look at even this last small part of the photosphere. I recommend looking at the Diamond Ring using a safe solar filter. That way when the total eclipse starts, your eyes will be more dark adapted so you can see more structure in the corona. More importantly, you will still be able to see when it is time to drive home! Most people that have seen the Diamond Ring directly saw it at the end of the eclipse. That is when I have seen it. It is the signal to look away from the Sun. It would be prudent to do so before the Diamond Ring but in my experience, most people don’t. The key is the duration of your look. I will not attempt to estimate a safe duration. I will only say it should be less than the time it takes to burn an image of it on your retina.

Gia on the beach
Dan diving a shipwreck
The total eclipse my wife and I saw in Aruba was on February 26, 1998. I was teaching science at Los Gatos High School and this was before we had a week break in February. I pitched the trip as a science expedition to my principal and he approved my one week absence. I arranged for our best substitute teacher to take all my classes for the entire week and met with him beforehand. The Exploratorium was going to show the eclipse live from Aruba on something called the Internet. I showed the sub how to connect my CRT TV to my Mac and how to log in to the Exploratorium website using an application called Netscape. If things went well, one of my classes would be able to see the total eclipse live, others would see the partial phases on the Exploratorium’s broadcast.

Warned to not be under sleeping iguanas
The eclipse stamp shows Aruba was prepared
Aruba is a Caribbean island near the coast of Venezuela. It is very dry and the weather prospects were excellent. The southern tip of the island was closest to the center line, but we elected to watch from the beach outside our hotel. We gave up 25 extra seconds of totality but also a long bus ride into an uninhabited area. People started setting up for the eclipse a couple of hours before totality. I was surprised by how many people asked what was going on. They just happened to schedule a vacation in the path of a total eclipse. What luck!
This may be the most laid-back place to view a total eclipse
I took a few shots of the partial phases through my 80 mm refractor with a solar filter. Just before totality I wedged my video camera in a palm tree and aimed it toward my psoition and the ocean. I hoped to catch the Moon’s shadow approaching. I sat on the beach and awaited a spectacle that must be seen in person to appreciate. Someone near me was watching the time and shouted out fairly accurate and helpful time estimates of second and third contact. After the diamond ring appeared I looked up and gazed in slack-jawed wonder. I then alternated viewing through the refractor and naked eye views. I took a lot of pictures, bracketing the exposure I had determined would be the best for the corona. I took a few very short ones to try and show the chromosphere and some long ones to try and get Jupiter. I also hoped to get the Diamond Ring. My plan was to look for it visually and take the shot without looking in the camera viewfinder. It turned out pretty well with maybe a bit too much diamond, not enough ring.
No large prominences :(
Long exposure shows Jupiter and moons but smeared Moon
Picture of Diamond Ring worth risking equipment, but not eyeball
It did not get very dark during the total phase as you can see in the videos. I did not need a flashlight to see the exposure settings on my camera. It was interesting to hear all the noises during the total eclipse. People honked their horns, yelled, and set of firecrackers, much different than the sounds on a cruise ship. I also noticed birds flying back to their roosts prior to totality. There were a good number of people scattered along the beach but it wasn’t crowded. I am looking forward to seeing what it is like to observe a total eclipse in the large crowd I expect will be on the football field at Madras High School.

Beat this misaddressed postcard back
The photosphere has its charms too
After I returned, I learned my students were able to watch the first total eclipse ever broadcast live on the Internet. The live stream would not load all morning but my substitute kept trying and also let the students try. One of the best students to ever come through Los Gatos High gave it a try and got it working just before second contact. The drama added to their experience.

In my next post I will give details about the eclipse event conducted by Lowell Observatory at Madras High School in Oregon. I will describe my plans for contributing to this event and some ideas for activities you can do to enhance your experience on August 21st.

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