News Excerpt
An international team of solar physicists led by those from Peking University, China, and National Center for Atmospheric Research of the United States has measured the global magnetic field of the Sun’s corona, or outer atmosphere, for the very first time.

    The Sun is a magnetized star, and its magnetic field plays a critical role in shaping the solar atmosphere.
    The magnetic field governs many aspects of the Sun's behaviour, leading to an 11-year solar cycle, spectacular solar eruptions, and the heating of the hot gas (plasma) in the solar corona to millions of degrees Celsius.
    There are two main puzzles about the Sun which this advancement will help address.
    First is the coronal heating problem. Though the core of the Sun is at a temperature of about 15 million degrees, its outer layer, the photosphere is a mere 5700 degrees hot. However, its corona, which stretches up to several million kilometres beyond its surface, at a temperature of one million degrees or more.
    Popular attempts to explain this puzzle invoke the magnetic field of the corona. Hence the present work will help understand and verify these theories better.
    The other set of questions pertain to the mechanisms of eruptions of the Sun, such as solar flares and coronal mass ejections. These are driven by magnetic reconnections happening in the Sun’s corona.
    Magnetic reconnection is a process where oppositely polarity magnetic field lines connect and some of the magnetic energy is converted into heat energy and kinetic energy which leads to the generation of heating, solar flares, solar jets, etc.
    The team used an existing technique known as coronal seismology or magneto-seismology to measure the coronal magnetic field.
    This method requires the measurement of the properties of magnetohydrodynamic (MHD) waves and the density of the corona simultaneously.
    The team used the improved measurements of the Coronal Multi-channel Polarimeter (CoMP) and advanced data analysis to measure the coronal magnetic field.
    CoMP is an instrument operated by High Altitude Observatory, of the U.S. It is located at Mauna Loa Solar Observatory, near the summit of that volcano on the big island of Hawaii.
    It is very important to measure the corneal magnetic fields regularly since the solar corona is highly dynamic and varies within seconds to a minute time scale.
    While photospheric magnetic fields are measured regularly from space, the measurement of global coronal magnetic fields was missing in the past since the coronal magnetic fields are very weak.
    While ground-based measurements pose challenges, Aditya-L1 satellite will aim to measure the solar coronal magnetic fields regularly. This will help understand the spectacular solar eruptions and predictions of space weather and many more things.

Aditya L1 mission
    It is India’s first mission to explore the sun.
    It is placed in the halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system which has the major advantage of continuously viewing the Sun without any occultation/ eclipses.
    It will provide observations of Sun's Corona (soft and hard X-ray, Emission lines in the visible and NIR), Chromosphere (UV) and photosphere (broadband filters).  
    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.   

Photosphere, corona, Sunspot, Earth magnetism