July 2, this year, is a special day for a team of researchers from the Indian Insititute of Science Education and Research (IISER) Kolkata as a total solar eclipse becomes visible in parts of Chile and Argentina. The team has given out a computer model-based prediction of the shape of the Sun’s atmosphere that the eclipse will reveal. Many Indian and international solar physicists will be gathering in Argentina to observe the eclipse and discuss the Sun’s influence on our space environment. If the Indian prediction works, it will help us forecast how the Sun’s temperament can affect space weather. This, in turn, can help monitor the safety of the electronic sensors in satellites, astronauts’ well-being and even the impact on Earth.
The corona
The Sun’s corona, which is like the Sun’s atmosphere, although hotter than its interior, is less dense and therefore emits fewer photons. Therefore, in normal times, the Sun’s surface shines so brightly that it obscures the corona. Only when there is a total solar eclipse does the solar disc get ‘occulted’ by the moon, exposing the corona to our view, albeit using instruments for photographing it.
The Sun’s magnetic field lines stretch out from the surface and permeate the corona. Solar plasma wind and storms including flares and coronal mass ejections are born in coronal magnetic field. Emergence of magnetic field from below the Sun’s surface and dynamic restructuring in the outer layers changes the shape of the corona. Now a team of researchers from IISER Kolkata, has found a way to predict the shape of the corona well in advance.
Two-step process
The team uses a two-step process to predict the shape of the corona. Using a model for the way the magnetic fields emerge as sunspots and evolve on the sun’s surface, they first predict what will be the form of the sun’s surface magnetic field on the day of the eclipse. Then, they use another model to extrapolate this to reveal what the corona will look like.
The coronal brightness and structure are determined by the magnetic fields of the Sun, which emerge out of the surface and spread out into the corona. “Using computational models, we have predicted the Sun’s surface magnetic field on the day of the eclipse. We used this as input to generate the prediction for the coronal field,” says Dibyendu Nandi from Center of Excellence in Space Sciences and IISER, Kolkata, who led the research.
Coronal regions which have more intense, closed petal-like loop structures appear brighter because the underlying magnetic fields heat the corona and control its emission. “Observations of these bright and dark structures in the corona during the eclipse can tell us whether our underlying computational models are correct or need more refinement,” Prof. Nandi adds.
According to their calculation, the occulted Sun will show two petal-like formations on either side of the corona with extended plume like structures stretching out into the solar system from their tips. It is to be noted that while solar north points upwards on paper, the eastern side is to the left and western side is to the right, unlike the conventions for geographical maps.
The eclipse will last for four minutes and 33 seconds. It will be visible during sunset in parts of Chile and Argentina.
Published - June 29, 2019 07:20 pm IST
