紫金山天文台太阳黑子手描观测记录的精度分析∗

摘要

太阳黑子是太阳上最显著的观测特征,也是最早开始系统记录的太阳活动现象.自从望远镜发明以来,人类已经拥有约400 yr系统的手描黑子观测记录.关于太阳活动的长期演化及其主要的11 yr周期变化在较大程度上依赖于这样单一的观测记录.近些年来,这些手描黑子图正在进行数字化,以利于长期保存和进行计算机处理.在未来,手描黑子记录的观测方式将不可避免地由CCD直接的数字化图像取代,因此分析过渡时期并存的两种方式所得到的资料的共同特性,以及它们之间的差异对于传统的手描黑子资料及其与未来纯数字化黑子资料的衔接很有必要.首先对数字化后的189张2011年紫金山天文台手描黑子观测记录进行了仔细的误差分析,得到所使用的扫描仪在水平和垂直方向比例尺相差0.2%,记录纸上太阳环本身的印刷误差导致东西方向比南北方向长度短1%.在扫描过程中的纸张的放置方向误差可达0.5◦.在对这些误差进行修正以后,将手描黑子记录与同时刻的空间SDO/HMI(Solar Dynamics Observatory/Helioseismic and Magnetic Imager)全日面连续谱图像进行对比,通过重叠的办法找出对应的黑子,并测量出手描的黑子观测精度约为7 arcsec,另外大约有3%的手描黑子无法找到对应的黑子记录.%Sunspot is the most significant feature in solar disk, and the earliest record of the solar activities. It has been systematically observed for about 400 years after the invention of telescopes. The long-term evolution of solar activities, especially the 11 year solar cycle, has been obtained based on these data to a great extent. In re-cent years, the historical hand-drawing records of sunspot are processed digitally for permanent preserving and computer processing. The hand-drawing records of sunspot will be eventually replaced by the CCD image in the future, therefore it is necessary to evaluate the accuracy of hand-drawing records by comparing them with the CCD image. In this study, 189 digital hand-drawing records of sunspot observed by Purple Mountain Observatory in 2011 are analyzed. The results include: (1) the scanner scale difference between horizontal and vertical directions is 0.2%;(2) the ring of the Sun on the recording paper is not a perfect circle, and the diameter in the east-west direction is 1%shorter than that in the north-south direction;(3) the orientation error of the record paper can reach up to 0.5 degree in scanning. After comparing the sunspot position of hand-drawing records with the simultaneous SDO/HMI (Solar Dynamics Observato-ry/Helioseismic and Magnetic Imager) images of continuous spectrum by overlapping method, we find that the accuracy of sunspot position in hand-drawing record is about 7 arcsec. There are roughly 3% of the hand-drawing sunspots whose corresponding sunspots in SDO/HMI images can not be found.