PREDICTION OF THE CORONAL MAGNETIC FIELD STRUCTURE
Figure caption: Our primary prediction, the coronal magnetic field structure of the Sun on 14 December 2020 is depicted on the left. Magnetic field lines are indicated by coloured curves (closed loops are indicated in black). The magnetic fields are plotted in a region confined within the Sun’s surface and 2.5 R (solar radius). An empirically derived white light image of the corona expected on 14 December 2020 is depicted on the right. Our prediction indicates a streamer (petal-like) structure on the Sun’s east limb (left edge) stretching from the northern to the southern hemisphere. The streamer tip is pointed southwards of the equator. This will manifest as a petal-like streamer in white-light coronal images close to the Sun, with an extended plume like structure visible further away in large-angle coronagraphs beyond 2.5R. On the west limb (right edge) we predict more diffuse and extended multi-part streamer structures. These appear to be associated with segregated and distinct closed-loop structures in the northern and southern hemispheres. In near-Sun white light observations these are expected to manifest as inhomogeneous extended structures (relatively more bright over the closed loop regions) across a wide range of latitudes from the solar north to the south. In large-angle coronagraphs, extended plumes are expected over-lying the major closed-loop structures, one each in the northern and southern hemispheres.
PREDICTED MAGNETIC MAP OF THE SOLAR SURFACE
Figure Caption: Utilizing a long-term calibrated Solar Surface Flux Transport (SFT) model, the CESSI-SSFT model, the solar surface magnetic field is evolved. By forward running this model the surface distribution of the Sun’s magnetic field is predicted for 14 December 2020. The last solar active region input in this model was on 7 December 2020. This predicted surface map serves as our input to the coronal field extrapolation model. For technical details on the CESSI-SSFT model refer to Nandy et. al. 2018, Astrophysical Journal, Vol 853, No 1 (https://doi.org/10.3847/1538-4357/aaa1eb) and Bhowmik & Nandy 2018, Nature Communications, Vol 9, Article 5209 (https://doi.org/10.1038/s41467-018-07690-0).
ADDITIONAL CORONAL MAGNETIC FIELD MAPS
Figure Caption: An additional rendering of the coronal field is depicted above to provide a slightly different perspective of the coronal field map from the same predicted coronal magnetic field data. These illustrate that coronal field rendering is a bit of an art and there could be minor variations depending on various renderings, however, broad features match across different field line visualizations.
ABOUT THE 2020 SOLAR ECLIPSE
A total solar eclipse would be visible across some parts of Chile, Argentina and the South Pacific on 14 December, 2020. Solar eclipses occur when the Moon occasionally comes in between the Sun and the Earth blocking the bright disk of the Sun. During total eclipses, because the intense radiation from the Sun’s disk is occulted by the Moon, the faint outer corona of the Sun becomes visible. The Sun’s corona is super-hot, reaching millions of degrees and is structured by the magnetic fields of the Sun that emerge from its interior and permeate the outer atmosphere. The Sun's coronal magnetic field is notoriously difficult to observe and constrain and theoretical computational models must be relied upon for gaining insight on the coronal structure. Observations of the Sun’s corona, performed during total solar eclipses can be used to confirm predictions from theoretical models of the Sun’s coronal magnetic field.
HOW DO WE MAKE THE SOLAR ECLIPSE PREDICTIONS
Novel utilization of two disparate computational models based on a theoretical framework postulated in Nandy et al. (2018) allows prediction of the Sun's coronal magnetic field structure. To predict and infer the structure of the coronal field expected during the eclipse, we use a data driven solar surface flux transport model (with in-built memory over multiple years). This computational model is forward run to 14 December 2020 to predict the Sun's surface field distribution (with the last solar active region incorporated on 7 December, 2020). The predicted surface field distribution for 14 December 2020 is subsequently used as input in a potential field source surface model to generate the coronal structure. This technique is complementary to numerically more expensive, full magnetohydrodynamic simulations, and can be implemented relatively fast, based on modest resources that are available to us.
The synthetic white light corona is generated from the predicted coronal fields by assigning more weight to closed field lines relative to the open field lines, and utilizing a combination of filters to approximately capture the density stratification of the corona.
REFERENCES TO RELEVANT MANUSCRIPTS
"Prediction of the Sun's Coronal Magnetic Field and Forward-modeled Polarization Characteristics for the 2019 July 2 Total Solar Eclipse", Dash S., Bhowmik P., B S A., Ghosh N., Nandy D., ApJ, 2020, Vol 890, Num 1, link
"Prediction of the Sun's Corona for the Total Solar Eclipse on 2019 July 2", Dash S., Bhowmik P., Nandy D., RNAAS, 2019, Vol 3, Num 6, link
"The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations", Nandy D., Bhowmik P., Yeates A. R., Panda S., Tarafder R., Dash S., The Astrophysical Journal, 2018, Vol 853, Num 1, link
"Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions", Bhowmik P., Nandy D., Nature Communications, 2018, Vol 9, Num 5209, link
ADDITIONAL INFORMATION ON 14 DECEMBER 2020 SOLAR ECLIPSE
Soumyaranjan Dash (CESSI, IISER Kolkata)
Arnab Basak (CESSI, IISER Kolkata)
Shaonwita Pal (CESSI, IISER Kolkata)
Suvadip Sinha (CESSI, IISER Kolkata)
Dibyendu Nandi (CESSI and Department of Physical Sciences, IISER Kolkata, India)
PAST CONTRIBUTORS TO ECLIPSE PREDICTION METHODOLOGIES
Prantika Bhowmik (CESSI, IISER Kolkata)
Anthony R. Yeates (Department of Mathematical Sciences, Durham University, UK)
Suman Panda (CESSI and Department of Physical Sciences, IISER Kolkata)
Rajashik Tarafder (CESSI and Department of Physical Sciences, IISER Kolkata)
Athira BS (CESSI, IISER Kolkata)
POINT OF CONTACT
Dibyendu Nandi: dnandi @ iiserkol . ac . in
The eclipse prediction campaign is conceived and led by Dibyendu Nandi at CESSI – a multi-institutional Center of Excellence established and funded by the Ministry of Education, Government of India under the Frontier Areas of Science and Technology Scheme. We acknowledge utilization of data from the NASA/SDO HMI instrument maintained by the HMI team and the Royal Greenwich Observatory/USAF-NOAA active region database compiled by David H. Hathaway. We are grateful to Prosenjit Lahiri for design and maintenance of this website.
IMAGE AND DATA SHARING
The images and data on this webpage have been uploaded for the usage of the community of interested scientists and the public who fund our research. It is free to use and disseminate, with due acknowledgement.
Link to the data files:
LINKS TO PAST CESSI SOLAR ECLIPSE PREDICTION PAGES
Eclipses have long been the subject of fantasies for humankind in a bid to understand the heavens. Interest in this phenomenon can be traced back to as early as 3340 BC in Ireland where petroglyphs exhibit a consistent understanding of tracks of the Sun and moon. Further records are obtained around 2134 BC in China where early philosophers recorded the event describing it as “an inharmonious meeting of the Sun and the Moon”. Descriptions of transitions in colors during solar eclipses have been recorded in ancient Indian texts such as Pancavimsa Bramhana. These vividly described color transitions match modern descriptions of solar eclipses. By 500 BC, the Babylonian and Greeks had already developed crude methods to predict the time solar eclipses. However, the mysticism around eclipses remained till much into the middle ages. Confirmation bias fed to the belief that eclipses portended the death of emperors.
This mysticism, however, proved to be a windfall for astronomy as emperors concerned by this phenomena began to fund philosophers to study eclipses. It resulted in the first accurate sky maps and studies of the path of heavenly bodies. Around 130 BC, Hipparchus used observations of an eclipse from different locations to estimate the size of the moon. In 1715, Halley used Newton’s laws of gravity to predict the position and time of the next solar eclipse. Though Haley was slightly off, it cemented dominance of Newton’s theories in English science. More attention came his way as his laws were used to calculate the trajectories of planets.
It was soon identified that the observations and calculations for the orbits of Mercury and Uranus slightly varied. A bid to explain Mercury’s orbit would eventually lead Einstein to work out his revised theory of gravity. In a triumphant demonstration of the scientific method, the solar eclipse of 1919 would again help Arthur Eddington verify Einstein’s Theory of General Relativity.
Total solar eclipses have historically provided us a unique opportunity to study the corona of the Sun. These observations are otherwise restricted due to the Sun’s bright photosphere. Observations during eclipses have therefore been the tools to understand the magnetic structuring, dynamics and physical construct of the Sun’s million degree corona.
Though the first reported reference of the corona can be traced back to Leo Diaconus of Constantinople in 968 AD, the first scientific ideas regarding the solar corona only emerged in the early 17th century. In 1605, Johannes Kepler suggested that the corona is light reflected due to the presence of material surrounding the moon. In 1724, Jose Jaoquin coined the term “Corona” and suggested that it is part of the Sun and not material surrounding the moon. More than a century later, the first wet plate photographs of the Sun’s corona were obtained in 1860 during a total solar eclipse. Currently, state of the art telescopes use occulting disks to create artificial eclipses to observe the solar corona.
Coronal magnetic field dynamics lead to solar magnetic storms (flares and CMEs) which hurl vast amounts of magnetized plasma (charged particles) in to interplanetary space creating hazardous space weather. Space weather impacts many of the technologies that we rely on today, including telecommunications, GPS navigational networks, electric power grids, air-traffic on polar routes and satellite operations. Observations of the solar corona during eclipses has the potential to constrain theoretical and computational models of coronal magnetic fields, which are expected to yield better forecasting capabilities for destructive space storms. These observations can also constrain the physical processes that heat the Sun’s corona to a super-hot million degrees and make it glow when the disk is shrouded by the dark side of the moon.
The above compilation of historical facts, anecdotes and scientific information has been collected from various sources which are referenced below.
1. Website for Paul Griffin: http://www.astronomy.ca/3340eclipse/
2. Website: https://Sunearthday.nasa.gov/2006/locations/babylon.php
3. Website: http://www.astro.cornell.edu/academics/courses/astro201/hipparchus.htm
4. Pasachoff, J. M. (1999), “Halley and his maps of the Total Eclipses of 1715 and 1724” Journal of Astronomical History and Heritage’ (ISSN 1440-2807), Vol. 2, No. 1, p. 39-54
5. Dyson, Frank W., Arthur S. Eddington, and Charles Davidson. “A determination of the deflection of light by the Sun's gravitational field, from observations made at the total eclipse of May 29, 1919”. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 220.571-581 (1920): 291-333.
6. Totality - Eclipses of the Sun (3rd edition) by Littmann, Espenak, and Willcox
7. “Images and Astronomy” by Kirit J. Sheth
8. Website:- https://umbra.nascom.nasa.gov/spartan/coronagraphs.html
9. “Solar storm risk to the north American electric grid” - Llyod’s, and Atmospheric and Environmental Research
10. Website: http://www.astronomeer.com/eclipses/index.html
11. Schrijver, C.J. et al. (2015), “Understanding Space Weather to Shield Society: A Global Roadmap for 2015-2025 Commissioned by COSPAR and ILWS”, Advances in Space Research, Vol. 55, Page 2745
12. Subbarayappa, B V, 2008, Traditions of Astronomy in India and Jyotishshastrs, Centre for Studies of Civilizations, Vol IV part 4, Centre for Studies of Civilisations, Viva Books