Coronal Prediction for the December 4, 2021 Total Solar Eclipse

Preliminary Prediction

[Our Final Prediction is now available]

New for 2021: Visible and Infrared Line Emission!
Brightness (Newkirk Filter)
Log Brightness (Unsharp Masked)
Click on the images to see slideshow of larger versions

This is our preliminary prediction of the solar corona for the December 4, 2021 total solar eclipse. The above images show two versions of the predicted white light brightness in the corona. The left image shows an image processed to simulate what would be seen when using a "Newkirk" radially graded filter. The image on the right is the brightness on a log scale, sharpened using an "Unsharp Mask" filter. These are two different attempts to approximate what the human eye might see during the solar eclipse.

The Sun is in the early phase of the new solar cycle, so the solar magnetic field is evolving rapidly. The corona's appearance can change significantly in several days. We will be posting a final prediction about one week before the eclipse (~November 27). Further changes between then and December 4 are possible (and indeed, likely), making prediction more difficult than at the time of the July 2, 2019 eclipse.

The image below on the left shows a digital processing of the brightness using a "Wavelet" filter to bring out the details in the image. The image on the right shows traces of selected magnetic field lines from the model. Additional details about the eclipse and our prediction model are given below.

Brightness (Wavelet Filtered)
Magnetic Field Lines
Click on the images to see slideshow of larger versions

These images are aligned so that terrestrial (geocentric) north is up, for the time of totality (07:33 UT) at the place of greatest duration just off the coast of Antarctica. This is the view of the Sun that would be seen by an observer on Earth with a camera aligned so that vertical is toward the Earth's north pole. Because the eclipse will be visible in the southern hemisphere, many of the photographs you see may have the south pole near vertical instead. Here is the perspective for a spectator on land or sea looking up. In the magnetic field line image, the Sun's surface shows the intensity of the radial component of the photospheric magnetic field. The brightest colors show the location of active regions (strong magnetic fields). Images in a coordinate system aligned with solar north are also available.

Volume-rendered Squashing Factor Q
(Eclipse Day View)
Volume-rendered Squashing Factor Q
(Rotating Movie)
Click on the image to see larger version | Click here to download movie

The last set of images show a special visualization of the three-dimensional (3D) magnetic field. By tracing magnetic field lines at extremely high resolution, we can calculate a 3D map of the so-called squashing factor - a scientific measure designed to indicate the presence of complex structuring in the magnetic field. We then integrate the map along the line-of-sight, with special weightings to create a composite that resembles solar eclipse images. This is intended to highlight the inherent complexity of the Sun's magnetic field and its intimate connection to visible emission from the solar corona.

Modeling the Corona for the Total Solar Eclipse

On December 4th, 2021, a total eclipse of the Sun will be visible over Antarctica and parts of the South Pacific off of the southern tip of Chile. The eclipse will be visible quite low in the sky, staying under 20 degrees in altitude. The longest duration of totality will be about 1 minutes and 54 seconds, occurring just off the coast of Antarctica. To see an interactive map of the path of the eclipse, please visit Xavier Jubier's interactive Google map. Also see Fred Espenak's Eclipse website for a detailed narrative of the eclipse circumstances and additional maps.

On November 7, 2021, we started an MHD computation of the solar corona, in preparation for our prediction of what the solar corona will look like during this eclipse. After about a week of calculations, this preliminary prediction was posted on November 15, 2021. For the prediction, we used data measured by the HMI magnetograph aboard NASA's SDO spacecraft. We used a combination of HMI synoptic maps, including data for Carrington rotation 2249 combined with data from a part of Carrington rotation 2250 measured up to 12:00 UTC on November 7, 2021. We also used a special method to account for unobserved data at the poles.

Our prediction is based on a magnetohydrodynamic model of the solar corona with a wave-turbulence-driven (WTD) methodology and improved energy transport. We have applied the WTD methodology to heat the corona previously, first in our prediction for the August 21, 2017 eclipse. This particular simulation employs other updates to our technical approach for the WTD formalism and the heating parametrization to better match the current solar conditions. This simulation is also quite large for this type of calculation, using 66 million grid points. For details about our model, please see our MAS Model Webpage and publications.

From our model, we can predict quantities that can be observed directly. We provide images of the total brightness (B) and the polarized brightness (pB). The B resembles what is seen by the naked eye. However, pB is the more scientifically useful quantity. Traditionally, pB has been used to separate light scattered by the K-corona and the F-corona. The K-corona is the photospheric light scattered by electrons in the corona, while the F-corona is the photospheric light scattered by dust, which is unpolarized. Note that we do not model the F-corona so its contribution to B is not included.

New for this prediction, we estimate emission from coronal lines in the visible and infrared Having both collisional and radiative excitation components, these lines provide unique information about the solar corona. We hope to compare these with measurements made by scientists from land, sea, & air during totality.

We can also estimate emission in extreme ultraviolet (EUV) wavelengths and X-rays. The EUV emission can be compared with solar observations from the AIA instrument on SDO. X-ray emission can be compared with solar observations from the XRT instrument on Hinode.

You can read the technical details about the calculations that were used to make our predictions.

Additional Materials

Polarized Brightness
Coronal Emission
Magnetic Field Lines


For technical details about our model, please see the following publications:

Other Resources for the Solar Eclipse


Our work is supported by NASA (Heliophysics Supporting Research and Living with a Star programs), AFOSR, and NSF. We are grateful to NASA's Advanced Supercomputing Division (NAS) for a allocations on the Pleiades, Electra, and Aitken supercomputers, as well as the Extreme Science and Engineering Discovery Environment (XSEDE) for allocations on the recently commissioned Expanse supercomputer at the San Diego Supercomputer Center (SDSC), which allowed us to complete the eclipse prediction simulations shown here. We also thank the SDO/HMI team of the Solar Physics Group at Stanford University for their support in providing timely access to HMI Synoptic magnetograph data.

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