选址与日冕观测组知识库

现代日晕光度计(Sky Brightness Monitor,SBM)是一种测定天文址点白昼大气参量的精密仪器,它已成为国际上太阳选址工作的重要设备之一。与国外同类设备不同的是,云南天文台研制的现代日晕光度计上的CCD相机系统可以被简单拆卸并保存,有利于选址踏勘阶段的携带和运输。为获取组装现代日晕光度计设备时可能存在的CCD离焦所导致的测量误差,于2011年6月在新疆奇台县和宁夏石嘴山市利用当地稳定的日照条件做了多次CCD大离焦量快变试验。统计结果表明,现代日晕光度计的CCD显著离焦可造成的相对测量误差约在6%之内。在正常情况下,即观测者基本按照物镜旋筒刻线标志在望远镜上安装CCD设备时,日晕测量的相对误差一般远小于6%。因此认为这种系统误差对优良址点的测量影响基本可以忽略。

A modern sky brightness monitor(SBM) is a precision instrument used for measuring various atmospheric parameters for an astronomical site during daytime.SBMs are important instruments for site survey programs.The SBM designed in the Yunnan Observatory can be easily dismounted from the main telescope tube by separating the CCD system,which makes it convenient for packing and transportation in the first stage of the site survey in the West China.In order to study possible measurement errors included when assembling the CCD system or in trips,we made a few CCD defocusing experiments during the site survey at Qitai(in Xinjiang) and Shizuishan(in Ningxia) in June 2011.Our statistical analysis shows that even with an obviously defocused CCD,the relative error in measurements is still within 6%.Usually,if the CCD is installed following the line marked on the T-thread nosepiece the relative error should be far less than 6%.Therefore,we think that the error caused by defocusing can be ignored,especially for excellent astronomical sites.