International Space Agencies – Missions and Discoveries

Explained: Solar Cycle 25


From UPSC perspective, the following things are important :

Prelims level : Solar Cycle, solar maxima and minima

Mains level : Solar Cycle and its impact

NASA and the National Oceanic and Atmospheric Administration (NOAA) has announced the commencement of solar cycle 25.

Try this PYQ:

Q. Which one of the following reflects back more sunlight as compared to the other three?

(a) Sand desert

(b) Paddy cropland

(c) Land covered with fresh snow

(d) Prairie land

What is the Solar Cycle?

  • Like seasons on Earth, the Sun follows a cycle of 11 years, during which solar activities fluctuate between solar minima and maxima.
  • Depending on the number of sunspots detected on the Sun, scientists term it is as solar maxima (highest number of sunspots) or solar minima (lowest number of sunspots).
  • Sunspots are small and dark, yet cooler areas formed on the solar surface, where there are strong magnetic forces.
  • They start appearing at Sun’s higher latitudes and later shift towards the equator as a cycle progresses.
  • In short, when the Sun is active, there are more sunspots in comparison to fewer sunspots during the lesser active phase.
  • Maxima or minima is not a specific time in the 11-year cycle but is a period that can last for a few years.

How are solar cycles determined?

  • One of the important elements researchers look out for on the Sun’s surface is the number of sunspots.
  • A new cycle commences when the Sun has reached its lowest possible minima phase.
  • Every time the cycle changes, the Sun’s magnetic poles reverse.

Monitoring solar cycles

  • Since the Sun is a highly variable star, data of sunspot formation and its progress need close monitoring.
  • Data of six to eight months are required to confirm whether the star has undergone a minima phase.
  • Traditionally, telescopes were used to record sunspots and recorded data since 1755 is available.
  • With the advance in technology in recent decades, satellites are also used to make real-time sunspot observations.
  • On this basis, scientists announced the completion of solar cycle 24, which lasted between December 2008 and December 2019.
  • With the Sun’s activities having reached its lowest minima between the two cycles, the new solar cycle 25 has now commenced.

How has the transition between solar cycles 24 and 25 been?

  • The Sun’s activities were notably lesser during 2019 and early 2020. There were no sunspots for 281 days in 2019 and 181 days in 2020.
  • Since December 2019, the solar activities have slowly picked up, corroborating the beginning of the news cycle.
  • The panel termed solar cycle 25 to be a weak one, with the intensity similar to that of Solar cycle 24.

What solar activities affect us on Earth?

  • Solar activities include solar flares, solar energetic particles, high-speed solar wind and Coronal Mass Ejections (CME).
  • These influence the space weather which originates from the Sun.
  • Solar storms or flares can typically affect space-dependent operations like GPS, radio and satellite communications, besides hampering flight operations, power grids and space exploration programmes.
  • CMEs pose danger to space weather. Ejections travelling at a speed of 500km/second are common during solar peaks and create disturbances in Earth’s magnetosphere, the protective shield surrounding the planet.
  • At the time of spacewalks, astronauts face a great health risk posed by exposure to solar radiation outside Earth’s protective atmosphere.


Notify of
Inline Feedbacks
View all comments