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  • 18 April, 2021

  • 15 Min Read

Sun's Atmosphere, ARIES Facility and Aditya-L1

ARIES Facility will host the support center for Aditya-L1

Sun’s Atmosphere

  • The atmosphere of the sun is composed of several layers, mainly the photosphere, the chromosphere and the corona.
  • It's in these outer layers that the sun's energy, which has bubbled up from the sun's interior layers, is detected as sunlight.


  • The lowest layer of the sun's atmosphere is the photosphere. It is about 300 miles (500 km) thick. This layer is where the sun's energy is released as light.
  • Because of the distance from the sun to Earth, light reaches our planet in about eight minutes.
  • The photosphere is marked by bright, bubbling granules of plasma and darker, cooler sunspots, which emerge when the sun's magnetic field breaks through the surface.
  • Sunspots appear to move across the sun's disk. Observing this motion led astronomers to realize that the sun rotates on its axis.
  • Since the sun is a ball of gas with no solid form, different regions rotate at different rates. The sun's equatorial regions rotate in about 24 days, while the polar regions take more than 30 days to make a complete rotation.
  • The photosphere is also the source of solar flares:
  1. Solar flares are the tongues of fire that extend hundreds of thousands of miles above the sun's surface.
  2. Solar flares produce bursts of X-rays, ultraviolet radiation, electromagnetic radiation and radio waves.


  • The next layer is the chromosphere. The chromosphere emits a reddish glow as super-heated hydrogen burns off.
  • But the red rim can only be seen during a total solar eclipse.
  • At other times, light from the chromosphere is usually too weak to be seen against the brighter photosphere.
  • The chromosphere may play a role in conducting heat from the interior of the sun to its outermost layer, the corona.


  • The third layer of the sun's atmosphere is the corona.
  • It can only be seen during a total solar eclipse as well.
  • It appears as white streamers or plumes of ionized gas that flow outward into space.
  • Temperatures in the sun's corona can get as high as 3.5 million degrees Fahrenheit (2 million degrees Celsius).
  • As the gases cool, they become the solar wind.
  • The Corona is up to 300 times hotter than the photosphere despite being farther from the solar core. This has remained a long-term mystery which is solved just recently.

Mystery of Sun’s Atmosphere solved

  • Indian Institute of Astrophysics, Bengaluru was also a part of the team.
  • At the core, the temperature of sun is ~ 15 million °C. At the surface layer or Photosphere it is just 5700°C.
  • Still further outwards, at the Corona, the temperature is ~1 million °C (But doesn’t decrease).
  • This is because of geyser like jets known as Solar Spicules that emanate from the interface (hairlike projections) of Corona and Photosphere.
  • The team used 1.6 meter Goode Solar Telescope at the Big Bear Solar Observatory (BBSO), the World’s largest solar telescope with the NIRIS instrument.
  • They took many high spatial resolution images of the same region of Sun within a short time known as High cadence.


  • Recent research suggests that tiny explosions known as nanoflares may help push the temperature up by providing sporadic bursts reaching up to 18 million F (10 million C).
  • The explosions are called nanoflares because they have one-billionth the energy of a regular flare.
  • Despite being tiny by solar standards, each packs the wallop of a 10-megaton hydrogen bomb. Millions of them are going off every second across the sun, and collectively they heat the corona.
  • Giant super-tornados may also play a role in heating the sun's outer layer. These solar twisters are a combination of hot flowing gas and tangled magnetic field lines, ultimately driven by nuclear reactions in the solar core.
  • Based on the detected events, we estimate that at least 11,000 swirls are present on the sun at all times.


  • Coronal holes are areas where the Sun's corona is colder, hence darker, and has lower-density plasma than average because there is lower energy and gas levels. Coronal holes are part of the Sun's corona and are constantly changing and reshaping because the corona is not uniform.
  • Prominences are anchored to the Sun's surface in the photosphere, and extend outwards into the solar corona. While the corona consists of extremely hot ionized gases, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere.
  • A solar flare is a sudden flash of increased brightness on the Sun, usually observed near its surface and in close proximity to a sunspot group. Powerful flares are often, but not always, accompanied by a coronal mass ejection.
  • A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the solar corona. They often follow solar flares and are normally present during a solar prominence eruption. The plasma is released into the solar wind, and can be observed in coronagraph imagery.
  • Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity.

What is Aditya-L1?

  • The Indian programme to study the Sun and the region between the Sun and the Earth from space – Aditya-L1 – is due to be launched next year.
  • It will carry seven payloads which have been developed by various institutions across the country.
  • Once the mission is launched, there will be a need for a ground support centre to monitor and coordinate the work on its various payloads.
  • This role will be played by the ARIES facility (short for Aryabhata Research Institute for observational Sciences) which is situated near Nainital.
  • In January 2021, an agreement was signed to this effect based on the proposal submitted by the ARIES team, led by Dipankar Banerjee, Director of ARIES, who is a solar physicist and co-chair of the science working group of the Aditya-L1 mission.
  • With about four to five personnel, this centre will come up at Haldawani, where ARIES is setting up a data centre also.

Guest users

  • Researchers who may not even be associated with core Aditya-L1 team will be able to book a specific payload to conduct observations for a particular time.
  • Any PhD student or postdoctoral fellow in a research institution can submit observing proposals through the online proposal submission system.
  • “The main aim of this centre is to let every researcher in India perform analysis over scientific data obtained from Aditya-L1. The total number of guest users will be from a few tens to a few hundreds,” says Prof. Banerjee.
  • A time allocation committee comprising senior and expert scientists will evaluate proposals based on their merit and feasibility to decide the priority. “We are open to users outside India by giving hand-outs of data analysis during international meetings and online training in the later phase of the mission,” he adds.

Studying lower corona

  • The Aditya-L1 Support Centre (ASC) will provide training through regular workshops for the guest users.
  • Apart from this, it will provide ready-to-use Python and Java apps for the satellite data and demos and handouts to facilitate the guest users.
  • An ARIES team has recently developed an algorithm to study the accelerating solar eruptions in the lower corona called CMEs Identification in Inner Solar Corona (in short, CIISCO), where CME stands for coronal mass ejection. Prof. Banerjee explains how this will be put to use: “The centre will also provide source code for advanced data analysis. For example, it will provide the source code for CIISCO that we have developed in ARIES to detect accelerating CMEs in the solar atmosphere.”
  • The group has also developed several advanced image processing algorithms to detect fine-scale structures in the solar atmosphere.
  • Such techniques are important to capture dynamics at different spatial and temporal scales. Prof. Banerjee gives an example of this: “While ISRO will provide raw and calibrated spectra of the solar atmosphere, at ASC we will further process the spectra to derive meaningful quantities such as intensity, Doppler velocities and line widths and provide these quantities to the scientific community.”
  • The facility will store co-aligned data from other observatories. That is, data taken at other wavelengths of observation than by Aditya-L1 and aligned in time and space so that they complement Aditya-L1 observations.

Significance of ARIES Facility

  • The centre will host a compendium of the location and duration of different features on the solar surface such as coronal holes, prominences, flares, CMEs and sunspots.
  • “We will employ automated methods to detect these features,” he says. Continuous monitoring of the location and duration of these features will help in monitoring the Earth directed CMEs and thereby, the space weather.
  • “Also, it will help us to understand the long-term evolution of these features and underlying physical mechanisms responsible for this,” says Prof. Banerjee.
  • “This centre will expand the visibility of Aditya-L1 beyond India at the international level.
  • Also, it will expand its reach within India. It will allow every interested individual to be able to perform scientific analysis of the data,” he adds.

Source: TH

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