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The sun we look at every day in visible light has a temperature of 6000 degrees Celsius. No sunlight means no life on our planet. But its outer atmosphere (corona) produces ultraviolet (UV) and X-rays. How can this heat flow from the cold (surface of the sun) to the million-degree hot corona, and not vice versa?
The first clues to the hot corona came from the 1869 eclipse observation of the 530.3 nm green coronal line. In 1941, Nobel laureate Hannes Alfvén concluded that the sun's corona is "heated to an extremely high temperature".
Bengt Edlén, an eminent Swedish physicist, identified green and red emission lines observed during the solar eclipse with highly ionized iron.
After seven decades of Nobel-prize winning discovery, these scientists are still investigating how far they are capable of heating the solar corona to high temperature.
The solar corona shapes the structure and dynamics of the heliosphere (a bubble-like region of space) in which all planets of our solar system reside. It is an inter-planetary magnetic field and creates space weather in planetary atmospheres, including our own.
Hazardous space weather events caused by solar activity (flares, coronal mass ejections, and all spells of eruptions) pose serious threat. This includes damaging satellite's electronics, changing the satellite's trajectory, increasing radiation dose to astronauts in space, disrupting global positioning and navigation systems, and tripping of power grids, etc.
Physics, plasma physics, plasma physics, physics, physics, physics, plasma physics, physics, plasma physics, physics, plasma physics.
Astrophysical plasma sources, specifically sun-like stars and their solar systems.
Even the main science goals of the "Parker Solar Probe" mission, launched on August 12, 2018, are to trace the flow of energy and to understand the heating of the solar corona and the acceleration of the solar wind.
Various ground and space-based solar observatories have reached the sub-arcsec (one arcsec = 725 km) resolution separating the region from a few tens to a few hundred kilometers. Several existing studies have been made by observing and understanding the sun, the discovery of helium, Evershed flows, several forbidden line spectra, Alfvén waves, neutrino oscillations, etc.
Kodaikanal Observatory (formerly known as Madras Observatory), which has been globally distributed in various research (USO / PRL, TIFR, IISc, IIA) and academic (IITs, IISERs, universities).
IIT (BHU) has a long track record of pursuing frontline research areas of solar physics starting from Skylab to Yohkoh spacecraft and later in the time of Solar and Heliospheric Observatory (SoHO) when several pioneering discoveries were made. Recently, IIT (BHU) has made a novel discovery under the leadership of Dr. AK Srivastava and his colleagues of confined pseudo-shocks in the sun's magnetised atmosphere. This research was published in the leading journal "Nature Astronomy" on October 8, 2018.
Pseudo-shocks were first theorized in supersonic flows in which way back in 1958 which decelerate to subsonic speeds. In the sun's atmosphere, they are not only affected by certain localized areas of growth. These pseudo-shocks carry enough energy and mass flow to the corona, which balance the coronal losses.
They are discovered as a new energy source in the sun's atmosphere. The newly-discovered pseudo-shocks will play a pivotal role in the frontline area of research in solar physics and astrophysics. This discovery is an important source of "green-energy". IIT (BHU) is at the forefront of this new discovery.
(The author is an institute professor in the department of physics, IIT-BHU, Varanasi.)
First Published: Oct 09, 2018 14:32 IST
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