In news

  • ISRO’s Aditya – L1 mission is similar to NASA’s Parker Solar Probe that is to study the sun.

Aditya-L1 mission

  • A Satellite placed in the halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system has the major advantage of continuously viewing the Sun without any occultation/ eclipses.
  • Therefore, the Aditya-1 mission has now been revised to “Aditya-L1 mission” and will be inserted in a halo orbit around the L1, which is 1.5 million km from the Earth.
  • The satellite carries additional six payloads with enhanced science scope and objectives.
  • The project is approved and the satellite will be launched during 2019 – 2020 timeframe by PSLV-XL from Sriharikota.
  • Aditya-1 was meant to observe only the solar corona.  The outer layers of the Sun, extending to thousands of km above the disc (photosphere) is termed as the corona.
  • corona has a temperature of more than a million degree Kelvin which is much higher than the solar disc temperature of around 6000K.
  • How the corona gets heated to such high temperatures is still an unanswered question in solar physics.
  • Aditya-L1 with additional experiments can now provide observations of Sun’s Photosphere (soft and hard X-ray), Chromosphere (UV) and corona (Visible and NIR).
  • In addition, particle payloads will study the particle flux emanating from the Sun and reaching the L1 orbit, and the magnetometer payload will measure the variation in magnetic field strength at the halo orbit around L1.
  • These payloads have to be placed outside the interference from the Earth’s magnetic field and could not have been useful in the low earth orbit.
  • The main payload continues to be the coronagraph (an instrument that blocks out light emitted by the sun’s actual surface so that the corona can be observed.) with improved capabilities.  

    Layers of Sun.

    • Sun Layers can be categorized into 2 sets.
    • Inner Layers.
    • Outer Layers.
    • The inner layers are the Core, Radiative Zone and Convection Zone. The outer layers are the Photosphere, the Chromosphere, the Transition Region and the Corona.

    Photosphere –

    • It is the deepest layer of the Sun that can be observed directly.
    • The temperature varies between about 6500 K at the bottom and 4000 K at the top (11,000 and 6700 degrees F, 6200 and 3700 degrees C).

    Chromosphere –

    • After Photosphere the next layer towards outside is chromosphere.
    • The temperature in the chromosphere varies between about 4000 K at the bottom (the so-called temperature minimum) and 8000 K at the top (6700 and 14,000 degrees F, 3700 and 7700 degrees C), so in this layer (and higher layers) it actually gets hotter if you go further away from the Sun, unlike in the lower layers, where it gets hotter if you go closer to the center of the Sun.

    Transition Region –

    • The transition region is a very narrow (60 miles / 100 km) layer between the chromosphere and the corona where the temperature rises abruptly from about 8000 to about 500,000 K (14,000 to 900,000 degrees F, 7700 to 500,000 degrees C).

    Corona –

    • The corona is the outermost layer of the Sun.
    • The temperature in the corona is 500,000 K (900,000 degrees F, 500,000 degrees C) or more, up to a few million K.
    • The corona cannot be seen with the naked eye except during a total solar eclipse, or with the use of a coronagraph.
    • The corona does not have an upper limit. 

    (Credits NASA)


What Is the Sun’s Corona?

  • Our Sun is surrounded by a jacket of gases called an atmosphere. The corona is the outermost part of the Sun’s atmosphere.
  • The corona is usually hidden by the bright light of the Sun’s surface. That makes it difficult to see without using special instruments. However, the corona can be seen during a total solar eclipse.
  • During a total solar eclipse, the moon passes between Earth and the Sun. When this happens, the moon blocks out the bright light of the Sun. The glowing white corona can then be seen surrounding the eclipsed Sun.

Why is the corona so dim?

  • The corona reaches extremely high temperatures. However, the corona is very dim. Why? The corona is about 10 million times less dense than the Sun’s surface. This low density makes the corona much less bright than the surface of the Sun.

Why is the corona so hot?

  • The corona’s high temperatures are a bit of a mystery. Imagine that you’re sitting next to a campfire. It’s nice and warm. But when you walk away from the fire, you feel cooler. This is the opposite of what seems to happen on the Sun.
  • Astronomers have been trying to solve this mystery for a long time. The corona is in the outer layer of the Sun’s atmosphere—far from its surface. Yet the corona is hundreds of times hotter than the Sun’s surface.
  • A NASA mission called IRIS may have provided one possible answer. The mission discovered packets of very hot material called “heat bombs” that travel from the Sun into the corona.
  • In the corona, the heat bombs explode and release their energy as heat. But astronomers think that this is only one of many ways in which the corona is heated.


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