Aerial photograph of CTIO, Cerro Tololo
NOAO/AURA/NSF
On Tuesday at 16:38 p.m. local time, in an extraordinary stroke of celestial luck, the National Science Foundation’s Cerro Tololo Inter-American Observatory (CTIO) and the European Southern Observatory’s La Silla Observatory site in Chile will both go under the central shadow of the Moon for around two minutes. It will allow a glimpse of the Sun’s tenuous outer atmosphere, its precious solar corona, from two of humanity's major observatories.
Chance geography means many more astronomers than usual are in place to take measurements and images of the corona, something that’s impossible to see or study outside the brief totality of a total solar eclipse. However, it could be the last time that astronomers gather to study the solar corona.
Arthur Stanley Eddington, left; Albert Einstein, right.
Public domain
Ever since British astronomers proved Albert Einstein’s general theory of relativity was correct at an eclipse in 1919, solar scientists have been trying to tease out the workings of the solar corona and its magnetic field. However, exactly 100 years later the astronomical community is getting excited about an eclipse possibly for the last time.
“Next year, scientists will no longer have to wait for an eclipse to engage in cutting-edge research,” says David Boboltz, Program Director at the NSF. “NSF’s Daniel K. Inouye Solar Telescope, which begins operations in 2020, will allow direct imaging of the solar corona anytime, shedding light on fundamental questions regarding solar magnetic fields and the heating to over a million degrees of the coronal plasma.”
The Daniel K. Inouye Solar Telescope will contain a 13 ft./four meter telescope. It will be the biggest and highest-resolution solar telescope in the world, on Haleakalā, the highest peak on the Hawaiian island of Maui.
This artist’s impression shows how the total solar eclipse of 2 July 2019 could appear from ESO’s La Silla Observatory in Chile if there are no clouds. The Sun will be quite low in the western sky and, if the skies are clear, several planets and bright stars should be also visible.
M. Druckmüller, P. Aniol, K. Delcourte, P. Horálek, L. Calçada/ESO
A last hurrah?
The total solar eclipse on July 2 could, therefore, be the final eclipse that some solar scientists need to take advantage of, though there’s no doubting that the events of next Tuesday still constitute a precious opportunity.
It’s so very rare to have a total eclipse pass over an existing observatory with large telescopes. In the last fifty years it’s happened only twice; in 1961 at L’Observatoire de Haute-Provence in France and in 1991 at Mauna Kea in Hawaii. The next time it will happen will be at the upcoming "Great North American Eclipse" in 2024 at Canada’s Mont Mégantic Observatory, the largest astronomical observatory in eastern North America. However, right now, Chile is buzzing with astronomers ready for just over two minutes of totality ... and science.
The ‘Einstein experiment’ redux
There will a trio of attempts to repeat the so-called “Eddington Experiment”, an attempt by British astronomers Sir Arthur Eddington and Sir Frank Dyson to test Albert Einstein’s general theory of relativity at an eclipse in 1919.
- ESO: TAROT (Télescope à Action Rapide pour les Objets Transitoires—Rapid Action Telescope for Transient Objects) telescope, a fast moving optical robotic telescope.
- CTIO: 11-inch Celestron Nexstar Telescope with a Hyperstar and a high-speed ZWO camera
- Chile (site TBC): Solar-brating Einstein – Centenary Expedition
Juan Seguel of CTIO (center) with the University of La Serena students who will be participating in the Eddington Experiment on the summit of Cerro Tololo during the 2 July 2019 Eclipse. Left to right: Ana León, Sebastian Suarez, Juan Seguel, Gabriela Bustos, and Javier Segura.
University of La Serena
Chile vs. Albert Einstein
At the CTIO, a team of astronomers from the National Optical Astronomy Observatory and students from the University of La Serena will be recreating the 1919 experiment by attempting to detect the minute deflection of starlight caused by the Sun’s gravitational field using an 11-inch telescope. “One of the challenges faced in this eclipse is that it occurs when the Sun is low in the sky; increased atmospheric distortion and turbulence from the low elevation will make the measurements substantially more challenging and may overwhelm the subtle deflection of starlight,” says Rob Sparks at the NOAO. If they’re unsuccessful, there’s another chance on December 14, 2020, when another total solar eclipse will be visible from southern Chile. That one will be much higher in the sky, and much easier to repeat Eddington’s experiment. However, for the local students, that’s not the point. “The 2019 eclipse will be a unique opportunity that cannot be missed!” says Seguel at the University of La Serena.
The telescope domes at Cerro Tololo Inter-American Observatory in Chile open their shutters in preparation for a night of observing, as the sun sets.
T. Abbott and NOAO/AURA/NSF
Up on Cerro Tololo
Just south of the centreline in Chile’s Elqui Valley, this eclipse’s path of totality couldn’t be better placed for the CTIO, a complex of astronomical telescopes and instruments operated by the Association of Universities for Research in Astronomy (AURA) around 80 km to the east of La Serena, Chile, at an altitude of 7,241 ft./2,200m. It's part of the National Optical Astronomy Observatory (NOAO) along with Kitt Peak National Observatory (KPNO) in Tucson, Arizona, it’s home to the four-meter Victor M. Blanco Telescope and the 4.1-meter Southern Astrophysical Research (SOAR) telescope, and one of the two eight-meter telescopes of the Gemini Observatory. AURA also operates National Solar Observatory (NSO) at CTIO. Perhaps most importantly, it’s also the site of the planned Large Synoptic Survey Telescope, a giant panoramic camera that will photograph the entire available sky every few nights. It’s now under construction.
The total solar eclipse of 21 August 2017, which was visible from the United States. Around the Moon is the white glow of the corona, sculpted by the Sun's magnetic field.
ESO/P. Horálek/Solar Wind Sherpas project
Capturing the corona
An international team led by Jay Pasachoff of Williams College, Williamstown, Massachusetts, will measure the corona’s current color, shape, and temperature as a continuation of an experiment started in the 1990s. “Each glimpse we get of the Sun during a total solar eclipse—only a couple of minutes every 18 months or so—gives us a different set of features to look at,” says Pasachoff. “One of our interests is understanding the eruptions on the Sun that could damage all the satellites now orbiting the Earth, so when we measure the speeds of the coronal mass ejections we sometimes see at eclipses, our work has potential major security implications for us on Earth.” Pasachoff added is hoping that that observing from Cerro Tololo gives an especially clear view of the corona.
‘Solar Wind Sherpas’
The “Solar Wind Sherpas” from the University of Hawai’i will study the corona from three different locations across South America; Cerro Tololo and two locations in Argentina. “We will explore the physics of the solar corona through imaging and spectroscopy (breaking up the light into its component wavelengths),” says Shadia R. Habbal at the University of Hawai’i. This eclipse will be unique. "It occurs late in the afternoon and the Sun will be at very low altitude," says Habbal. "Also, the Sun is close to solar minimum, so the distribution of structures in the solar corona will be different from in 2017.”
Field lines of a solar coronal magnetic model.
National Solar Observatory (NSO)
The corona’s magnetic field
Magnetic structures in the corona explain the explosive events on the Sun’s surface that cause “space weather” that effects on the Earth. So a team from the University Corporation for Atmospheric Research (UCAR) will investigate the magnetic field of the Sun’s corona. “The only way to measure the magnetic field is to measure the polarization of the light,” says Paul Bryans, lead researcher. “We will do this at the eclipse by using polarizers on our telescope … they work in exactly the same way as sunglasses, blocking light that is polarized in a certain direction. By rotating these polarizers, we can piece together the shape of the magnetic field on the Sun. This will help us understand what types of magnetic field configurations can lead to eruptive events.”
The ‘hidden corona’
A team from the Solar Science Observatory of National Astronomical Observatory of Japan will take images of the corona from across Chile and Argentina, areas that space-borne “eclipse-making” observatories like NASA’s LASCO and STEREO coronagraphs cannot see. The goal is to make a complete image of the corona. “We are going to collaborate with amateur observers, widely spread along the total eclipse path in Chile and Argentina, to organize multi-site observations,” says team leader Yoichiro Hanaoka. “It will be a great achievement for citizen science.”
Illustration of the Moon’s shadow during an eclipse.
NSO/AURA/NSF
It’s not all about the Sun
A team from the Institute of Astrophysics of the Canary Islands, will observe changes in the Earth’s atmosphere during totality, such as drops in temperature. “A total solar eclipse produces a broad, round area of darkness and greatly reduced sunlight that travels across Earth’s atmosphere in a relatively narrow path during the daytime,” says M. Serra-Ricart. “Its effect on solar radiation intensity is remarkably similar to what happens at sunrise and sunset and it creates changes in the Earth’s atmosphere we want to measure.”
The sun sets behind the New Technology Telescope (NTT) at ESO's La Silla observation site.
Iztok Boncina/ESO
What’s going on at Chile’s La Silla Observatory?
As well as having 1,000 lucky visitors to a special event who won tickets in a lottery, the regular inhabitants of ESO’s La Silla Observatory will take astronomical observations in unusual ways. Some scientists will use its NTT, ExTrA, TAROT, and REM telescope, while others will bring their own.
- CesaR (ESA/ESAC): Scientific observations of the solar atmosphere and the Earth’s ionosphere, as well as general observations for outreach and education.
- ExTrA (IPAG): Test the ExTrA telescope on a very unusual type of transit.
- OPC NTT (Institut d'Astrophysique de Paris–CNRS, Sorbonne Universities, and Institut d’Astrophysique Spatiale/Université Paris-Sud): Spectrographic measurements with the 3.58-metre NTT (the first in the world to have a computer-controlled main mirror) of the solar corona, as well as fast imaging from a small telescope of the corona. The NTT observations will improve on those done in 1991 at Mauna Kea in Hawaii.
- PACA_SolPol19 (Space Science Institute): Measurement of linear polarization of solar K-corona and eclipse outreach activities.
- REM (INAF): Imaging of the eclipse with the Rapid Eye Mount (REM) telescope in various wavelengths. REM is usually dedicated to the follow-up of gamma-ray bursts.
Whatever happens, expect iconic images of an eclipsed Sun beside an observatory dome. That would be a fitting photo for what promises to be the "astronomers' eclipse."
Wishing you clear skies and wide eyes
Disclaimer: I am the editor of WhenIsTheNextEclipse.com
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