Uncovering Intense Ancient Solar Activity from Naked-eye Observations of Egg-like Sunspots

Abstract

Abstract Ancient sunspot records written in classical Chinese provide important information regarding ancient solar activity. The Chinese recorded 14 observations of sunspots that resembled an egg (hereafter, egg record; the word egg is used to represent approximate sunspot sizes) before 1000 CE. However, the egg records in classical Chinese were too short to provide sufficient sunspot details. This study was conducted to decode egg records from 1769 and 1917 through telescopic sunspot observations. The results of our decoding show that egg-like sunspots were generally used by observers in East Asia to represent a very large sunspot group with an approximately elliptical outline. An egg record generally served as a marker of intense solar activity. Three egg records (in 1278, 1769, and 1917) were observed to be close to the solar maxima, with the time difference being smaller than 1 yr. Some egg records could thus be used to identify the solar maxima. The mean time difference between 10 egg records and the nearest solar maxima is 2 yr. Therefore, egg records can provide necessary information for uncovering additional intense solar activity from ancient times.