Precision Full Disk Solar Photometry

最近对太阳的精确光度观测表明它是一颗变星。综合太阳光的卫星观测和地面太阳边缘光度测定表明，在一个太阳周期内，亮度变化约为0.1%，当太阳黑子较多时亮度更亮。地面测光表明，太阳的纬向有效表面温度分布在一个太阳周期内是变化的，这种变化不能用太阳黑子和普通光斑随时间变化的通量过剩和不足来解释。太阳亮度如何影响陆地气候？越来越多的统计证据表明，一些地方的天气测量与太阳活动有关。由于我们刚刚注意到太阳活动（即太阳黑子数）与太阳通量相关，因此推测一些天气变化是由微小的通量变化引起的很有吸引力。蒙德极小期是太阳黑子数量较少的时期，因此太阳通量可能较小。与此同时，欧洲大部分地区的平均气温较低。本项目将1)以相当的精度和更高的空间分辨率，将精密翼缘光度测量扩展到圆盘中心；2)在接近太阳极大期的两年时间内，测量光斑、太阳黑子和背景热通量贡献的太阳周期变化。总体目标是阐明太阳光度变化背后的机制，并将其与太阳活动联系起来。这样就有可能重建近代史上的太阳变化，并将其与气候变化联系起来。

Recent precision photometric observations of the sun have shown it to be a variable star. Satellite observations of integrated sunlight, and ground-based solar limb photometry suggest that the luminosity varies by about 0.1% during a solar cycle, being brighter when there are more sunspots. The ground- based photometry suggests that the latitudinal effective surface temperature distribution of the sun varies over a solar cycle, and this change is not accounted for by the time dependent flux excess and deficit of sunspots and ordinary faculae. How does the solar luminosity affect terrestrial climate? There is growing statistical evidence that some local measures of weather are correlated with solar activity. Since we have just noted that solar activity (i.e., sunspot number) is correlated with the solar flux, it is appealing to speculate that some weather variations are caused by the small flux changes. The Maunder minimum, a time of few sunspots and thus perhaps a smaller solar flux, was coincident with a period of colder mean temperatures in much of Europe. The program funded here will 1) extend the precision limb photometry measurements to disk center with the comparable precision and higher spatial resolution, 2) measure the solar cycle variation of the faculae, sunspot, and background thermal flux contributions for two years during a period near solar maximum. The overall aim is to elucidate the mechanism behind solar luminosity variations and relate these to solar activity. It might then be possible to reconstruct solar variability over recent history and relate that to climate change.