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Saturday, September 26, 2020

Explained: Sunspots, and why they occasionally spark worry

When a Sunspot reaches up to 50,000 km in diameter, it may release a huge amount of energy that can lead to solar flares.

By: Explained Desk | New Delhi | Updated: August 11, 2020 9:37:58 am
Solar flares, when powerful enough, can disrupt satellite and radio transmission, and more severe ones can cause ‘geomagnetic storms’ that can damage transformers in power grids. Image: NASA

A massive Sunspot group, AR2770, was observed last week, spaceweather.com claimed using images of the Sun’s surface from NASA’s Solar Dynamics Observatory (SDO). According to the report, a few minor space flares have been emitted by this particular Sunspot group already, which has not caused anything major other than “minor waves of ionization to ripple through Earth’s upper atmosphere”.

Solar flares, when powerful enough, can disrupt satellite and radio transmission, and more severe ones can cause ‘geomagnetic storms’ that can damage transformers in power grids.

Sunspots

A Sunspot is an area on the Sun that appears dark on the surface and is relatively cooler than surrounding parts. These spots, some as large as 50,000 km in diameter, are the visible markers of the Sun’s magnetic field, which forms a blanket that protects the solar system from harmful cosmic radiation.

On the photosphere– the outer surface of the Sun which radiates heat and light– Sunspots are the areas where the star’s magnetic field is the strongest; around 2,500 times more than the Earth’s magnetic field.

Most Sunspots appear in groups that have their own magnetic field, whose polarity reverses during every solar cycle, which takes around 11 years. In every such cycle, the number of Sunspots increases and decreases.

The current solar cycle, which began in 2008, is in its ‘solar minimum’ phase, when the number of Sunspots and solar flares is at a routine low.

In this false-color image of the sun, intense magnetic fields are denoted by yellow (- polarity) and green (+ polarity). Image: Spaceweatherinitiative/NASA SDO

Why Sunspots appear dark

Because Sunspots have high magnetic pressures, the atmospheric pressure in the surrounding photosphere reduces, inhibiting the flow of hot gases from inside the Sun to the surface.

Due to this, the temperatures of Sunspots are thousands of degrees lower than the surrounding photosphere, which has a temperature of 5,800 degrees Kelvin. Sunspots temperatures are around 3,800 degrees Kelvin.

Because they stop the convective flow of heat and light, Sunspots appear dark. They typically consist of a dark region called the ‘umbra’, which is surrounded by a lighter region called the ‘penumbra’.

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Solar flares and Coronal Mass Ejections

When a Sunspot reaches up to 50,000 km in diameter, it may release a huge amount of energy that can lead to solar flares. The flares are caused by explosions that are triggered due to the twisting, crossing or reorganising of magnetic field lines near Sunspots.

At times, solar flares are accompanied by Coronal Mass Ejections (CME)– large bubbles of radiation and particles emitted by the Sun that explode into space at high speed. CMEs can trigger intense light in the sky on Earth, called auroras.

The solar flare explosion’s energy can be equivalent to a trillion ‘Little boy’ atomic bombs dropped on Hiroshima and Nagasaki in 1945.

Also in Explained | To what extent did the Covid-19 lockdown affect global temperatures?

Damage caused by solar flares

Solar flares can have a major effect on radio communications, Global Positioning Systems (GPS) connectivity, power grids, and satellites.

In 1967, a major solar flare almost led to a nuclear war during the Cold War, as per a space.com report. In May that year, the US Air Force’s Ballistic Missile Early Warning System radar sites in Alaska, Greenland and the UK got jammed due to the flare, causing US officials to mistakenly hold the Soviet Union responsible for the radar failures. It was only after scientists at the North American Aerospace Defense Command (NORAD) informed US leaders of the solar flare that the matter deescalated.

Recently, scientists have developed a new model that can successfully predict seven of the Sun’s biggest flares from the last solar cycle, out of a set of nine with the help of NASA’s Solar Dynamics Observatory.

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