It happened once more, as predicted by Pythagoras and Galileo’s Music of the Spheres. Our Moon passed in front of our Sun, just far enough this time that it didn’t quite hide it all the way to its borders. The Sun’s Corona was not revealed but created what has been called a ring of fire.
I have had the pleasure to watch several solar eclipses in my life, including total ones and believe me: nothing matches a total solar eclipse! Next best to me are annular eclipses like the one we just saw across the American continent. I got to see one as a child and I remember very well watching it with a solar filter on my telescope.
Costa Rica, where I live, was not quite in the best place to see the ring. We just got a more darkened than usual partial eclipse. What to do? I decided to photograph the light spots formed by tree leaves that are actually a pinhole-camera like projection of the Sun. Instead of being round they look like crescent moons during a partial solar eclipse.
Yes, I also got a photo of the Sun when clouds were moving in and I was able to make a photo without filters.
Have you seen the little crescents on the ground before?
Partial solar eclipse in Costa Rica, near noon, just as clouds moved in.A couple that was watching the crescent-like solar eclipse projected images on the sidewalk.Crescent-like solar-eclipse images formed by the trees on a pedestrian bridge at the University of Costa RicaA detail of the solar eclipse images formed by diffraction from the openings amongst the leaves of the trees.
The Rio Celeste is formed at the junction of two mountain rivers with crystalline waters that originate on the slopes of Tenorio Volcano, in Northern Costa Rica. One is clean water Buenavista River. The other is Quebrada Agria (Sour Creek) which owes its name to the fact that it contains dissolved sulfuric acid, aluminum and silica. When the two streams come together at the site known locally as the “Teñidero,” (Dyeing Shop) the mixture produces a suspension of particles with sizes less than a thousandth of a millimeter that scatters the blue component of sunlight and gives Río Celeste its beautiful turquoise color.
Although very clean water sometimes appears blue in the ocean, rivers and lakes, this is because water can slightly absorb light in the red part of the spectrum and lets the blue part through. However, this effect is very weak and is only noticeable when the water is several meters deep. The most common, however, is that due to the presence of algae or suspended mineral particles, the water of many rivers looks greenish, reddish or brown.
When water looks turquoise in waters of glacial origin or in volcanic regions such as Rio Celeste, we also notice that it is not completely transparent due to suspended material and its color is due to Mie Scattering. It receives this name in honor of the German physicist Gustav Mie who was the first to describe the mathematics of the phenomenon. The exact color of the scattered light depends on the size of the particles and the light source, but it is usually a blue-green or cyan color, close to what we know as “celeste” in Spanish. The blue (actually cyan) color of the sky is also due to the scattering of light, in this case by molecules in the atmosphere and is called Rayleigh scattering which is a special case of Mie scattering when the particles are much smaller than the wavelength of light.
The white light of an LED flashlight passes through a container with a little milk diluted in water. Casein particles in milk that are about 0.2 μm (micrometers) in size first scatter the blue component of light, and the transmitted light is yellowish. Milk also contains fat particles of about 1 μm and these, due to their larger size, weakly scatter some yellow light.
In glacial waters and in the Rio Celeste, visible light falls on particles with a size comparable to its wavelength, which is 0.4 to 0.7 micrometers (thousandths of a millimeter). In these cases, the reddish component of the spectrum, of longer wavelengths, continues on its way but the bluish component deviates in all directions, that is, it is scattered. As the rays are scattered in all directions, part of the light we see directly from the above the water surface but another part is in turn reflected by other particles towards us. In the meltwater of glaciers this is produced by finely ground rock particles called “Glacial Flour.” In Costa Rica we do not have glaciers but the lake of Poas Volcano’s active crater shows a similar light-blue color due to Mie scattering of light in this case by colloidal sulfur particles. Let us note that in the scattering of light the color does not correspond to that of the material of the particles because they are not large enough to be directly observed. For example, during our investigations we have found that Río Celeste particles are in fact a complex mixture of colorless silicon and aluminum minerals.
The author in Perito Moreno Glacier, Argentine Patagonia. The glacier mainly shows the blue color of pure water while the lake appears turquoise due to Glacial Flour particles.
To further understand the color phenomenon of Rio Celeste we would have to delve into Mie’s Theory of electromagnetic wave scattering. We will define scattering as the change in direction that waves experience when they encounter in their path obstacles of a size comparable to their wavelength. An everyday example of scattering are sound waves that change their direction at doors and that is why we can hear sounds from other rooms even if we do not have a direct line of sight to the source. The mathematics of the Theory are complicated but the theory successfully explains all scattering processes from the color of the sky to the operation of Radar. In the references there is an article illustrating the change in color of scattered light as a function of particle size and the more physically and mathematically inclined can then read it and learn more about it on the internet.
In the “Blue Pond” you can see that water of Río Celeste is a little greener than the color of the sky. The exact observed color depends on environmental factors such as the color of the river bottom and the power spectrum of the illuminant, in this case the direct Sun.
Image. In the “Blue Pond” you can see that water of Rio Celeste is a little greener than the color of the sky. The exact observed color depends on environmental factors such as the color of the river bottom and the power spectrum of the illuminant, in this case the direct Sun.
Initially we managed to explain the color of Rio Celeste based on a mathematical model of Mie scattering developed by Dr. William Vargas from the School of Physics and CICIMA, University of Costa Rica, based on careful measurements of the size distribution and properties of the particles that form in the Teñidero made by Drs. Erick Castellón (School of Chemistry and CICIMA, UCR and Dr. Max Chavarría (also from the School of Chemistry, CIPRONA, UCR, and CENIBIOT) together with researchers from Costa Rica National University.
Dr. Erick Castellón analyzes particles using a Scanning Electron Microscope at the Center for Research in Materials Science and Engineering, CICIMA-UCR.
Our subsequent work has extended these initial results, giving us a clearer idea of how the particles are formed in the Teñidero. We now know that what occurs is a chemical reaction between the soluble species of sulfuric acid, silicic acid and aluminum from Quebrada Agria with the alkaline ions from Buenavista River. The reaction rapidly generates the colloidal aluminosilicate particles that scatter blue light in Río Celeste.
But, where do the acidity and ions of Quebrada Agria come from? The answer comes from other work we have done on the Río Roble, the tributary that joins the Rio Celeste at Laguna Azul (Blue Pond). Dr. Max Chavarría and his collaborators found that in the hydrothermal water and gas vents we see at Los Borbollones, underground hydrogen sulfide is oxidized to sulfuric acid by microorganisms:
H2S + 2 O2 → H2SO4 + energy
These are sulfur-oxidizing bacteria of the genera Sulfuriferula, Halothiobacillus and Sulfurimonas that take advantage of the chemical oxidation of sulfur with oxygen to obtain metabolic energy. The sulfuric acid produced by this reaction attacks the rocks, mainly dissolving the feldspars, with which the aluminum and silicon pass into the aqueous phase as Al3+ ions and silicic acid (H4SiO4).
Dr. Max Chavarría at a hydrothermal vent near Rincón de la Vieja Volcano, also in Northern Costa Rica. Although Quebrada Agria is not well explored yet, this is likely similar to the type of hydrogen sulfide sources in that acidify the water.A river turtle searches for food near the submerged hydrothermal vents in Los Borbollones. Roble River has a pH close to 3 and the water is even more acidic at this source with a pH of 2.3.
The Quebrada Agria (Sour Creek) originates as a common mountain river but comes into contact with hydrothermal vents such as those of Roble River which turn it into an acid current with a pH of 3-4 (an acidity between that of lemon juice and that of orange juice) due to the reaction with the rocks of the riverbed. The Buenavista River, with a pH of 7-7.5, like clean mountain rivers, contains basic bicarbonate ions (HCO3–) that can neutralize the acidity of sulfuric acid. In addition, the Buenavista River contains silicic acid, a product of the dissolution of siliceous shells of its abundant diatoms and also of the soils rich in volcanic glass on the slopes of Tenorio Volcano. The two currents resulting mixture acquires an intermediate pH of 5-6. At these pH values solid aluminum hydroxides begin to form but in the presence of silicic acid they quickly become a colloid of hydroxyaluminosilicate particles that scatter blue light.
The chemistry of Rio Celeste :
First, bicarbonate ions from the Buenavista River neutralize sulfuric acid from the Quebrada Agria:
2 HCO3– + H2SO4 → SO42- + 2 H2O + 2 CO2
But the Buenavista River is fast enough to leave behind unreacted bicarbonate, which produces hydroxide ions.
HCO3– + H2O → H2CO3 + OH–
Hydroxide ions react with aluminum ions from Quebrada Agria forming Al(OH)3
2 Al3+ + 6 OH– → 2 Al(OH)3
Finally, the silicic acid reacts with the aluminum hydroxide generating hydroxyaluminosilicates of approximate composition (Al2O3)(SiO2)2•3H2O as amorphous particles due to their rapid formation rate.
Río Celeste’s Teñidero is the point where Río Buenavista joins the small Quebrada Agria that can be seen in the background of the photograph. What appears to be a greenish-white formation are deposits of the mineral that precipitates at the mixing point. A few meters downstream the turbulent flow suspends the particles thus creating Río Celeste.
Note that if there were no silicic acid in Quebrada Agria then hydroxyaluminosilicates would not form. This is an important difference with respect to acidic rivers in other regions.
Hydroxyaluminosilicates belong to a group of minerals that do not form crystals and are known as Short-Range Ordered Aluminosilicates (SROAS). Their chemical bonds are similar to those of Imogolite and Allophane SROAS and they are found in volcanic soils called Andosols that are common in Costa Rica. Imogolite and Allophane have definite shapes of tubes and hollow spheres respectively. The hydroxyaluminosilcates for their part do not have such a defined structure.
Our group from the University of Costa Rica took water samples from the Río Celeste and isolated the particles by filtration through a very fine membrane. Next, we characterized the particles using Electron Microscopy, Powder X-ray Diffraction and Infrared Spectroscopy techniques at the School of Chemistry and at the Center for Materials Science and Engineering Research (CICIMA). By means of a comparison with the properties of synthetic SROAS just recently reported in the literature, we were able to verify that indeed the particles of the Río Celeste are recently formed hydroxyaluminosilicates. In the references you can consult the work that we did together with international collaborators in Germany and Sweden for the study of the microbial communities involved.
Hydroxyaluminosilicates are of great environmental importance as they keep aluminum ions, toxic to life, trapped within a highly insoluble solid, separating them from drinking water. The environmental chemistry of silicon and aluminum are thus closely linked and affect all biological systems.
The Rio Roble (Oak River) joins the Celeste River at the Laguna Azul (Blue Pond). This could actually be a second Teñidero since Rio Roble is as acidic as Quebrada Agria. However, at this point Rio Celeste no longer contains as many basic bicarbonate ions and its flow lacks turbulence so the second precipitation occurs slowly.
We owe our success in the study and exploration of the Río Celeste system to the support of the National System of Conservation Areas (SINAC) and especially to the energy and enthusiasm of Master Isaac López Núñez who currently manages Tenorio Volcano National Park. We are deeply grateful to him and the Park staff for their support.
We conclude by mentioning that in Costa Rica we also find rivers with blue waters on the slopes of Poás and Rincón de La Vieja volcanoes and we are also investigating them. These other blue rivers in Costa Rica are just as beautiful but they take on their color slowly, over several kilometers. As far as we know, they do not seem to have a Teñidero like the one on Río Celeste. Observing two colorless streams that join in the middle of the tropical forest and instantly turn into a river with waters dyed the color of Heaven is a natural miracle that Costa Ricans must witness and admire.
1. Hydrotermal sources inject sulfide (as H2S) into the Agria Creek. 2. Sulfur Oxidizing Bacteria oxidize sulfide to sulfuric acid (H2SO4) and convert Agria Creek into an acidic stream. 3. Sulfuric acid dissolves aluminum and silicon in rocks forming aluminum ions (Al3+) and dissolved silica (H4SiO4). 4. The Buenavista River is rich in dissolved silica, diatoms, and alkaline bicarbonate ions. (HCO3–). 5. The partial neutralization of the acid from the Agria Creek when mixed with the alkaline ions from the Buenavista River causes the aluminum ions and dissolved silica to combine, forming amorphous colloidal particles of hydroxyaluminosilicate in the Teñidero. 6. Colloidal hydroxyaluminosilicate colloidal particles measuring tenths of a micrometer scatter the blue component of the spectrum of the solar light sand produce the observed color of The Celeste River. Diagram by Solange Voysest.
Further Reading
Arce-Rodríguez, A.; Libby, E.; Castellón, E.; Avendaño, R.; Cambronero, J. C.; Vargas, M.; Pieper, D. H.; Bertilsson, S.; Chavarría, M.; Puente-Sánchez, F. Out of the Blue: The Independent Activity of Sulfur-Oxidizers and Diatoms Mediate the Sudden Color Shift of a Tropical River. Environmental Microbiome2023, 18 (1), 6. https://doi.org/10.1186/s40793-023-00464-2. – Our recent work on the characterization of Río Celeste particles and their formation mechanism. The main source for this post.
Beardmore, J.; Lopez, X.; Mujika, J. I.; Exley, C. What Is the Mechanism of Formation of Hydroxyaluminosilicates? Scientific Reports2016, 6 (1), 30913. https://doi.org/10.1038/srep30913. – A description of the initial stages of formation of hydroxyaluminosilicates.
Exley, C.; Guerriero, G.; Lopez, X. Silicic Acid: The Omniscient Molecule. Science of The Total Environment2019, 665, 432–437. https://doi.org/10.1016/j.scitotenv.2019.02.197. – Silicon and aluminum in biological systems. References to the authors previous work on this topic.
Levard, C.; Doelsch, E.; Basile-Doelsch, I.; Abidin, Z.; Miche, H.; Masion, A.; Rose, J.; Borschneck, D.; Bottero, J.-Y. Structure and Distribution of Allophanes, Imogolite and Proto-Imogolite in Volcanic Soils. Geoderma2012, 183–184, 100–108. https://doi.org/10.1016/j.geoderma.2012.03.015. – SROAS formation and discussion of tetrahedral and octahedral aluminum sites in their structure.
Arce-Rodríguez, A.; Puente-Sánchez, F.; Avendaño, R.; Martínez-Cruz, M.; de Moor, J. M.; Pieper, D. H.; Chavarría, M. Thermoplasmatales and Sulfur-Oxidizing Bacteria Dominate the Microbial Community at the Surface Water of a CO2-Rich Hydrothermal Spring Located in Tenorio Volcano National Park, Costa Rica. Extremophiles2019, 23 (2), 177–187. https://doi.org/10.1007/s00792-018-01072-6. – Source of water’s acidity in Los Borbollones.
I joke about me being too tall to see slime molds down there on the forest floor, but occasionally I get to spot them. Then comes the process of setting up my camera and tripod in the most awkward position possible and holding my breath for long exposures… I guess if macro photographers ever do yoga or free-diving they will be a force to reckon with in these disciplines.
These Myxos (I think they are Trichia or Hemitrichia) remind me of light bulbs. The fruiting bodies become reddish later.
There are three phases in the life cycle of slime molds that are very photogenic: The unopened fruiting bodies or sporangia, the equivalent of mushrooms; the already opened sporangia that held the spores; and the viscous liquid phase that crawls about, looking for nutrients. I think the latter one looks better in stop motion videos though.
These are the same white fruiting bodies after they opened.
These things are about a millimeter tall and require stacking macro images to get a good looking image. Luckily, my OM System OM-1 camera can do this automatically as long as I don’t need to do stack more than 15 photos. If more images are needed the camera will take as many as I want but then I have to stack them later using Helicon Focus. Either way it saves you from having to slowly slide the camera in a focusing rail to get each image for the stack.
The white Didymium growing on a leaf was an in-camera stack. You get a ready to use stacked jpeg and also saves the individual raw files in case you need them. The other ones are stacked using Helicon.
Finding a nice subject among these tiny organisms brings about a sense of discovery that certainly makes up for any technical hardships!
Didymium growing on a leaf. An in-camera stack ready to use.
Some landscape photography books and websites claim that sunset photos are amateurish and should be avoided by true Landscape Photographers as they are plain boring.
Really?
One of the most inspiring views in our planet is an spectacular sunset, or a sunrise if we are early risers. It is no surprise that we all aim up our cameras to remember and to share the view. I’ve seen simulations of Martian sunsets and they look sad and nearly colorless. I will not be a colonist there, trust me. In the Moon, with no atmosphere, they are just black!
So here I am, sharing yesterday’s sunset in my corner of our beautiful planet. I hope you will find it as pretty as it looked to me!
Last week I had the pleasure to hear a concert by the Orquesta de Costa Rica with vocals by La Colmena Performance Arts Center. They chose to sing pieces from well-known Musicals and did so remarkably well.
That day I was carrying my Olympus Pen-F and a couple of fast primes and, even though we were seated towards the back of the theater, I decided to do some viewer’s perspective photos. When I have this camera in my hands and am shooting people I always end up doing black and whites: it must be the looks of the camera body…
What you see here are not the in-camera black and whites as I had to do a little processing and cropping. If I’d had a chance to frame better the photos by moving around I’d probably be using the superb Pen-F originals.
I feel my approach gives the performer’s photos a nice classical look, but… what do you think?
Selected pieces from Musicals performed by Centro de Artes Escénicas La Colmena and the Orquesta de Costa Rica
An ultrawide lens (anything below 24 mm in 35 mm equivalent format) can provide a sweeping view of an open landscape, but I also find it important for crowded forest and tree covered environments.
The widest rectilinear lens I own is an 11 mm lens by Irix and it is an excellent lens, but these pictures are made with other lenses. They are landscapes I made while testing an ultra wide 11 mm lens by Venus Optics on my Z7 alongside a 12 mm Samyang fisheye lens. I no longer own either lens but the photos I made that afternoon are good representatives of what can be done with these optics.
A fisheye lens allowed me to frame the pastures with he branches literally above my head. By keeping the horizon near the center of the frame, it remains straight on a fisheye lens image.
One thing I sometimes dislike about ultra wide rectilinear lenses is that elements in the corners of the image can look too stretched, like sucked into the frame. Because of this, I sometimes actually prefer using a fisheye lens: when used carefully, one can can hide the strong deformation we associate with their extreme projection. By keeping the horizon near the center of the frame, it remains straight on a fisheye lens image. In other cases, the image can be reprojected (defished as some people call it) to avoid the curved corners.
Removing just enough of the fisheye distortion can provide a convincing ultra wide image without the light falloff that plagues rectilinear ultra wide angle lenses in the corners. A photo using the rectilinear Laowa 11 mm lens works fine and takes advantage of the stretching of the lower tree branch to give depth to the composition.
You can be the judge now and decide if this approach works as I really wanted to include nearby elements from a restricted point of view: I was literally shooting from a barbed-wire fence in all the photos I show here.
Have you tried using fisheye lenses for landscape photos?
Here are two images made from about the same viewpoint using the 11 mm rectilinear lens and the 12 mm fisheye. They are clearly not identical but both are very usable. Do you like one better than the other?
After seeing, and taking, many snapshots of the water on a sunny, tropical beach it is not difficult to notice that the water always looks frozen and the movement and intensity of the moment is missing.
The first time I saw photos of Slime Mold fruiting bodies, the equivalent of fungal caps, I couldn’t help thinking about life on another planet. The fact that these organisms actually turn into a slowly creeping slime when they are not in the reproductive stage sure helps my mental image of something alien.
These sporangia, a more technical name for the reproductive structure, are barely over one millimeter in length (one mm is about 1/24th of an inch). I am not very good at finding them, but there is a large and enthusiastic group of hobbyists and scientists that are constantly publishing photos of Myxomycetes, the technical name for the Slime Molds… they are good at finding these little marvels!
Arcyria incarnata sporangia: they remind me of a group of friends gossiping.
These are among the first ones I have photographed. As you know, I am more of a landscape/wildlife photographer but… Hey, one must adapt to pandemic life! I was lucky to spot them growing on some rotting wood logs on the back of my garden.
Arcyria incarnata sporangia or spore-bearing structures after opening.
My friend Federico Valverde was nice enough to identify them for me. He is a retired biologist that has found new fire for his scientific brain finding Slime Molds and photographing them. These beautiful Slime Mold species are named Arcyria incarnata.
One of the prettiest beaches on Costa Rica’s west coast is on the inside of a circular bay that gives protection to the swimmers from the open ocean waves and is named Carrillo Beach.
Visiting a new area in Costa Rica nearly always means a change in the avian species around. Granted, some birds seem to pop up anywhere but there are always nice surprises.
The place we were staying was on the slope of a hill, with a long balcony overlooking the coast. A few feet below the balcony the Stachytarpheta shrubs were busy with hummingbirds flying non stop.
Female Ruby-throated Hummingbird feeding on Stachytarpheta nectar.
The high viewpoint revealed the beautiful design on the tails of female Ruby-throated Hummingbirds. But I was not too successful in getting eye-level shots of the males… well, I already had those anyway from their seasonal visit to my garden’s Stachytarpheta.
Cinnamon HummingbirdBlue-throated Goldentail perched on a dry Stachytarpheta inflorescence.
Soon I noticed two species I had not photographed before: the Cinnamon Hummingbird and the Blue-throated Goldentail. The first, kindly chose a well-located perch and posed for me. The Goldentail I shot perched on a dry inflorescence… enough to show its blue throat, but it was again the elevated viewpoint from the balcony that provided a nice picture of both its thick red bill and its magnificent Golden Tail.
eduardo libby: photography blog 