EQUAL CONTRAST TECHNIQUE (Syllabus: GS Paper 3 - Sci & Tech)

Context: Scientists developed a new methodology, called Equal Contrast Technique (ECT), to analyze images of the Sun in white light can help obviate temporal and latitudinal variations in observations related to instrument and sky conditions. 

• It can help in accurate analysis of the historic time series of images of Sun and in understanding the dynamics of the sun, solar cycle variations, dynamo processes in the convection zone and resulting long term climatic variations on the earth.

Key Points

• It is known that there are large numbers of regions of weak magnetic field on the sun which vary with time.
• These can be studied using magnetograms and Ca-K line images of the sun as there is strong correlation between the magnetic field and the Ca-K line intensity of the region on sun. 
• The magneto-grams are available for short period and the characteristics of the instrument are changing with time. 
• Ca-K line images are available for long period at Kodaikanal observatory (KO), for more than 100 years with no change in the optics of the instrument.
• Similarly, other observatories in the world, such as Mount Wilson Observatory (MWO) have this type of data for about 70 years.
• Using the data obtained at Kodaikanal observatory the scientists have shown that correlation between derived plage area (bright region in the sun’s chromosphere) from the Ca-K images and sunspot number is excellent, even on daily basis, over a period of about 100 years for the first time.
• This type of accurate analysis of the historic time series of Ca-K images can be useful for reliable and accurate investigation of variations on the sun and the effect of this on the climatic condition of the earth.