An analysis of digital sunspot counting for determination of sunspot number from Langkawi National Observatory

Abstract

The Relative Sunspot Number (RSN) has been determined for centuries manually (visually) and internationally recorded by Solar Influence Data Center (SIDC). This has been the case even today due to strong goal of keeping the sunspot counting data consistent, dating back to the early 1600s. The RSN indicates the Sun's magnetic activities and therefore accurate detection and classification are fundamental. The active use of digital CCD cameras in modern astronomy today has made huge progress in this field. Hence, Langkawi National Observatory (LNO) is fully equipped to conduct astronomical researches digitally including its solar observatory setup. LNO solar observatory has been collecting daily solar images since early 2008, so a digital method of calculating the RSN needs to be developed that corresponds closely to the international RSN. Here, we present the methods, algorithm and results from a small program that was developed based on the data at LNO. The results are found to be consistent with a correlation value between the digital sunspot counting program and International RSN to be at R2 = 0.7851 for overall data and R2=0.9269 (93%) for good images. However this value varies with different quality of images and therefore a very simple method to differentiate the image quality had to be developed before any sunspot counting was done.