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
Why Sunspots appear dark
- 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.
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 reorganizing 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.
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.