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About The Equal Contrast Technique (ECT)


Recently, scientists developed a new methodology, called Equal Contrast Technique (ECT), to analyse Sun images in white light, which can help prevent temporal and latitudinal variations in observations related to instrument and sky conditions.


GS III: Science and Technology

Dimensions of the Article:

  1. Key Points
  2. Significance
  3. Magnetogram

Key Points:

  • The Sun exhibits numerous regions of weak magnetic fields that change over time.
  • Magnetograms and Ca-K line images are used to study these regions due to a strong correlation between magnetic field and Ca-K line intensity.
  • Magneto-grams have limited availability and instrument characteristics change over time.
  • Ca-K line images have long-term availability at Kodaikanal Observatory (KO) and other observatories like Mount Wilson Observatory (MWO).
  • Researchers used Kodaikanal data to establish a strong correlation between derived plage area (bright region in the sun’s chromosphere) from Ca-K images and sunspot numbers. This correlation is evident even on a daily basis over about 100 years.


  • Accurate analysis of historical Ca-K image time series provides reliable insight into sun variations and their impact on Earth’s climate.
  • Understanding sun dynamics, solar cycle variations, convection zone dynamo processes, and resulting long-term climatic variations on Earth is facilitated.


  • A magnetogram is an image captured by an instrument that is capable of detecting and depicting the strength and distribution of magnetic fields on the Sun’s surface.
  • In a magnetogram, different shades of gray are used to represent varying levels of magnetic strength.
  • The absence of a magnetic field is often represented by a neutral shade of gray.
  • Black and white areas on a magnetogram indicate regions where the magnetic field is particularly strong or weak, respectively.
  • This visualization technique helps scientists study the complex magnetic activity and patterns on the Sun, which play a crucial role in various solar phenomena and processes.

-Source: The Hindu, PIB

February 2024