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Sunspot drawings at Kodaikanal Observatory: a representative results on hemispheric sunspot numbers and area measurements

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dc.contributor.author Ravindra, B
dc.contributor.author Kumaravel, P
dc.contributor.author Selvendran, R
dc.contributor.author Samuel, Joyce
dc.contributor.author Kumar, P
dc.contributor.author Nancy Jassoria
dc.contributor.author Navneeth, R. S
dc.date.accessioned 2020-11-26T15:45:36Z
dc.date.available 2020-11-26T15:45:36Z
dc.date.issued 2020-01
dc.identifier.citation Astrophysics and Space Science, Vol. 365, No. 1, 14 en_US
dc.identifier.issn 1572-946X
dc.identifier.uri http://prints.iiap.res.in/handle/2248/7418
dc.description Restricted Access © Springer The original publication is available at springerlink.com https://doi.org/10.1007/s10509-020-3725-7 en_US
dc.description.abstract The importance of the periodicity in sunspot appearance was well recognized by the mid-19th century. Several observatories around the globe have made the record of sunspots in the form of drawings and preserved them safely for posterity. At the Kodaikanal Observatory (KO), the sunspot observations have begun in 1905. In those times observations were recorded on photographic plates and after the development of those plates in the laboratory, the drawings of the same were made on the Stonyhurst grids. In these drawings, called sun charts, different features on the sun’s disk, e.g., sunspots, plages, filaments, prominences, etc. were clearly identified and visually marked with different colors. We have collected 111 years of sunspot drawing spanning over 10 solar cycles. These sunspot drawings were carefully stitched to make bound volumes, each for every 6-months. The drawings are kept at the Kodaikanal library for scientific use and analysis. In this article, we describe briefly the process of drawing, methods of counting sunspot numbers and measurement of sunspot area using square grids. We have collected the data for the northern and southern hemispheres separately. From the collected data, we compute the sunspot number and area and compare it with Royal Greenwich Observatory (RGO) and Sunspot Index and Long-term Solar Observations (SILSO) data. The results show that the measurement of the sunspot number is underestimated by about 40%. The KO monthly averaged sunspot number data of both hemispheres is normalized with the RGO monthly averaged total sunspot number data. This procedure provided a good correlated data set that can be used for further scientific work in the future. The sunspot area data from KO is slightly underestimated in the first 5-cycles and seems mildly overestimated in the later 5-cycles. These data sets are valuable additions to the existing data of sunspot records. en_US
dc.language.iso en en_US
dc.publisher Springer en_US
dc.subject Sun-photosphere en_US
dc.subject Sun-sunspots en_US
dc.subject Sun-solar cycle en_US
dc.title Sunspot drawings at Kodaikanal Observatory: a representative results on hemispheric sunspot numbers and area measurements en_US
dc.type Article en_US


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