Saturday, July 13, 2019

#193 - Tuesday, July 2, 2019 - Solar Eclipse in Chile

The day finally arrived -- the solar eclipse over South America!  After a year of planning, the day was finally upon us.  I had packed my backpack and backpack camera case for my Sky-Watcher mount the night before, and I woke up at 5 AM to catch our 6:30 AM bus from a nearby hotel.  We decided to book our eclipse day with Ecoturismo, with whom we had a daytime boat tour of the islands off the coast of Chile a few days prior for spotting the Humboldt penguin, among other creatures.

We made a few stops along the way to the village of La Higuera, about 50 km north of La Serena, including a gas station that was packed with people also travelling for the eclipse.  But I successfully got my coffee, and everyone hit the bathroom and got some snacks, and we were on our way.

A large area had been set up just outside of the small village of La Higuera.  Many people just pulled their cars off the dirt road and set up chairs and BBQs.

Ecoturismo had a couple of tents set up with a bunch of chairs and a large BBQ for feeding us all day.

A mobile cell tower had been erected as well, although bandwidth was limited because there were so many people there.  Away from the area where most of us were was a series of white tents where several celebrities were said to be watching the eclipse.  

I took my time getting my gear set up after we selected a spot so I could make sure I had everything right.  It was only about 9:30 AM or something around there, and the partial eclipse didn't start until 3:22 PM.  I attached my Nikon D5300 equipped with my Nikon 70-300mm lens at 300mm to my Sky-Watcher Star Adventurer DSLR tracker mount.  To polar align it (roughly) in the daytime, I used my phone's compass and the tilt angle indicator of my phone using an app called GPS Status that I use all the time for astronomy.  I weighted down my tripod with an open sack thing I found on Amazon that velcros to tripod legs, and I filled it with some rocks that were lying around.  Then I plugged the mount into a cell phone battery and plugged my camera's USB into my tablet.  I had logged into BackyardNikon the night before and left it open, and I tested the capture speed (sometimes it will trigger pictures every 3.5 seconds instead of 2.5 seconds, depending on whether it thinks it's a USB connection or serial cable).  I put my Baader solar filter on the end of the camera lens -- it's a homemade one that was given to me with the Borg 76ED that I got from a fellow astronomy club member, and it was a little too big for my camera lens, so I lined it with bubble wrap before I left for Chile.  I aimed the camera at the sun and focused it, and then taped down the focuser.  Then I was all ready to go.

Then it was a long wait!  I walked around and took pictures, browsed Facebook, sat back and enjoyed the sunshine, and chatted with numerous passers-by who were curious and amazed with my rig.  Most of the other people in attendance didn't bring any cameras; they were just there to observe.  

Showing our tour guide Felipe the partially-eclipse sun through out solar binoculars.  It took some effort to convince people these were safe because of their special built-in filters, which means that they were well-educated on the risks!

Beside where my group was hanging out was a Chilean family, and a pre-teen boy was trying to figure out a way to capture the partial phases with his Canon DSLR after seeing the sun through our sun-oculars.  He cut up a pair of solar glasses and taped it to the aperture, but it wasn't big enough to cover the whole thing.  I helped him out (with my terrible Spanish), and we found some other cardboard pieces and tape to block the rest of the aperture. Then I helped him with the settings, and showed him how to chase the sun as it moved across the sky.  He was very grateful and excited!  I told him he could remove the filter during totality.

I checked my rig periodically and adjusted the camera as needed to keep the sun centered (my polar alignment wasn't perfect, obviously).  I did accidentally kick the tripod at one point, but it wasn't too hard to get it back where it needed to be.  Finally, we had first contact, and it was only a minute or so after that that we could see the moon just edging over the sun through our sun-oculars.  It was a few more minutes before you could see it without magnification through the solar glasses.

I went over to my tablet about a minute or so before the partial phase started and hit "go" on my partial phase script.  This took a few different settings of images every 5 minutes on repeat.  

As the moon covered more and more of the sun, the quality of the light started to degrade, and I started looking for the pinhole effect, where light shining through a hole would have the crescent shape instead of a fully-lit circle.  I was looking around for something with small-ish holes, since that's easier to see than criss-crossing your fingers, and I found it -- the chair on my traveling companion Chris' cane had holes in it that were perfect!  So I tilted the chair toward the sun, and sure enough, you could see half-moon-shaped shadows of the holes on the ground.  I looked up a couple words in Spanish to explain this to the people around me, and then went and showed a bunch of people the effect.  My friends called me the science ambassador!

At long last, totality drew near, and I went over to my laptop to prepare the script for totality, which I would start at one minute till.  I called out times in English and Spanish for the people around me, started the script, and took off the solar filter at 20 seconds.  I didn't need to call out the last 10 seconds because I great shout went up, and nobody could hear me anyway.  I watched the moon blot out the entire sun, and it was an utterly eerie and incredible sight.  The sky darkened suddenly, and the corona slowly brightened into view.  People were shouting and cheering, and I took a video on my other DSLR at the beginning of totality to capture the moment.  

My traveling companion Manning shoved a pair of binoculars into my hands saying he could see prominences, but I didn't see them.  I did admire the corona in the binoculars, something I missed during the 2017 solar eclipse in Wyoming.  Then I took some wide images of the eclipse with my other DSLR, and I looked around to see the 360 degree sunset.  It was mostly cut off for us by the mountains, but I could see it all along the west, where they were lower.  I also looked around for stars and planets, and saw quite a few!  Venus was shining very brightly below the sun, and I looked for Jupiter in the east, but I think it was too low behind the mountains.  I thought I saw Mars and Mercury, but I wasn't 100% sure it was them.  I saw several stars, including Sirius, possibly Rigel, Procyon, Canopus, Alpha Centauri, and Arcturus I think.  

Nikon D3100, 18mm, f/3.5, 1/50s, ISO-400

Because the sun was lower in the sky, it looked larger (much more so than the above image indicates), but the corona didn't appear to be as large as the one in 2017.  There were also no sunspots earlier, and there has been very little solar activity lately.  

Seeing the sun as a black hole surrounded by a shimmering halo is totally eerie.  Your brain doesn't quite know what to make of it.  It was beautiful, natural and alien at the same time.

Then, just like that, my phone solar eclipse app ("Solar Eclipse Timer" on Android at least) was announcing "glasses on!", and I watched the sun re-emerge, which was spectacular.  Then I put the filter back on my camera, and kind of stood there for a bit, unsure of what exactly to do.  It went by so fast, it felt like less than 10 seconds!  Finally I went to check on my images, and the last couple with the thin sliver through the solar filter looked a little out of focus.  My heart sank.  Were they all out of focus??  I scrolled through and checked -- they were, by just a hair.  I had taped down the focuser, but the zoom had slid back at some point, which put it a little out of focus.  However, I held out hope that they would still look good on a larger screen, as long as you didn't zoom in.  I got some cool shots!

Just before second contact
Nikon D5300, 300mm, f/5.6, ISO-200, 1/2500s

Inner corona
Nikon D5300, 300mm, f/5.6, ISO-200, 1/400s

Outer corona
Nikon D5300, 300mm, f/5.6, ISO-200, 1/8s

Diamond ring at third contact
Nikon D5300, 300mm, f/5.6, ISO-200, 1/800s

I didn't have the diffraction spikes in the 2017 images because I used a circular telescope aperture instead of the straight lines of the iris inside of a camera lens, but I think it's a cool effect.

I re-started the partial eclipse phase script, and we hung around as the moon moved away from the sun's disk.  We didn't get to see the sun completely re-emerge, however, since they sank behind the hills together, heading toward sunset.

Nikon D5300, 300mm, f/5.6, ISO-200, 1/2500s

Sunset was also a gorgeous moment to witness.

Finally, it was time to pack up and head back to La Serena.  Well, us, and 250,000 other people as it turned out!  It wound up taking us 4.5 hours to go the 50 km, and that was with our intrepid tour guide taking some American-style "shortcuts" around the other cars!  We finally got back to the hotel at 10 PM, and I stayed up for a little while longer to post a few images (after installing Lightroom so I could apply the watermarks).

It was a very long but incredible day!  It was an awesome experience sharing this solar eclipse with a few of my friends, strangers interested in astronomy, and many others who just wanted to witness this incredible spectacle.  

Does viewing two total solar eclipses in a row make me an eclipse chaser? :D

[ Update: July 7, 2019 ]

While I was waiting for the moon to set to go out and do some observing from the Atacama Lodge the second half of my trip to Chile, I processed some of my corona images together into a single composite image.  Cameras don't have as high of dynamic range as our eyes -- our eyes can see many levels of brightness at the same time, but the camera sees far fewer.  As you can see in my images above, shorter exposure times make the dimmer outer corona dark, while longer exposure times make the brighter inner corona too bright to see any detail.  There are many ways to process images to reveal multiple levels of brightness, such as people who make neat moon composites, the Milky Way behind brightly-lit foreground scenes (although this can sometimes also be done in a single shot with clever lighting), etc.  The method I used here is the same as the one I used for the 2017 eclipse, known as the Pellett method, described here by astrophotographer Jerry Lodriguss, and in more detail in the blog post made it about here.  

I won't put all the details here, since they are all in my blog post tutorial.  But here's the rundown.

First, I selected several images with different exposure times, ranging from 1/4000s to 1s, which turned out to be 10 for me.  Then, I radially blurred each one, and saved out those files as TIFFs.

Original (1/8s)


Next, I subtracted the two images from each other with an offset of 128 to get a low-contrast difference image between the two that pretty much just contains the streamers themselves.

Difference image

Then, I added all of the difference images together.

Difference images added together

Here, you can see the streamers, some prominences, and the edges of the sun, since the input images weren't all taken at the same time, so the moon had translated across the sun's surface a bit.  Next, I multiplied this image by the longest-exposure input frame.

Since the edges of the moon are messy and it didn't really stick around during the subtractions anyway, I copied the moon from one of the longer input images and enlarged it a bit to cover up the movement.  Finally, I toyed with the exposure, contrast, saturation, and denoising settings, and covered up a few dust spots using clone stamp, and have this final product!

So awesome!  You can see lots of detail in the corona, and even one of the little prominences.  It's a little hazy because it was quite low in the sky, only 13 degrees above the horizon, which made it a bit hazy.  One thing that is really interesting about the corona this time is how symmetric it is.  This is likely due to the solar minimum we've been in for a while, which also means we haven't seen much in the way of sunspots for about the past year.  So here's hoping that the 2024 eclipse across the US has even more excitement!  

One last note I'll make here for anyone who's wondering - my images are rotated about 45 degrees from the sun's true orientation as observed visually from the same spot.


Another really great thing about this eclipse in particular is that it crossed over so several professional observatories that exist in that area of Chile, including Cerro Tololo and La Silla, and a lot of research observations were taken at those locations.  Much is still unknown about the sun's corona, which is essentially the sun's outer atmosphere that extends billions of miles into space, encompassing the whole solar system.  It consists of charged particles of gas, and that gas has been superheated by some as-yet-unknown process to over one million degrees (that high, Kevlin, Fahrenheit, and Celcius are really all about the same), which is much hotter than the surface of the sun, which is about 5500 degrees C (10,000 F).  Even though it is so much hotter, it's dimmer because it's very tenuous and spread out.  

In addition to understanding the corona itself, the corona can tell us a lot about what happens on the sun's surface, as well as deeper inside, and can help us make future predictions for potentially electrical-grid-disrupting solar events.  In 1859, a massive solar storm known as the Carrington event disrupted telegraph communications, caused lines to spark and short, and even activated telegraph equipment that was disconnected from power.  Just imagine what something like that would do to today's electrical grids, computer systems, and satellites!

We have a few spacecraft that study the sun, including the corona, such as STEREO and SOHO.  SOHO has an obscuration disk that can be put into place to observe the sun's corona, but only as far out as three times the sun's radius, meaning we can't observe the inner corona at all -- except during a total solar eclipse.  

There are a variety of other interesting effects that are studied during total solar eclipses, such as the short-duration temperature changes, animal behavior, and how the temporary night-like conditions from a shadow that moves faster than the speed of sound across the surface of the Earth impact radio communications that bounce off the Earth's ionosphere at night.  Many of these projects involve citizen scientists who collect data to be processed by researchers.  There's a lot to do and see with eclipses!

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