卡拉尔阿尔托天文台（Calar Alto Observatory）
The night-sky at the Calar Alto Observatory
摘要：
我们提出了一个表征的主要性质的夜空在卡拉阿尔托天文台的时间段之间的2004年和2007年。我们使用光学分光光度数据，在无月观测期间拍摄的光度校准图像，以及天文台定期监测的观测条件，如大气消光和视宁度。首次导出了该天文台典型无月夜空的光谱。光谱显示出不同污染线的强烈污染，特别是来自水星的污染线，其对不同波段天空亮度的贡献在B，V和R中分别为~0.09 mag，~0.16 mag和~0.10 mag。在U、B、V、R和I波段，无月夜空表面亮度的天顶校正值分别为22.39、22.86、22.01、21.36和19.25等角秒^-2，这表明对于I波段的光学观测而言，卡拉阿尔托是一个特别黑暗的地点。天文有用夜的比例约为70%，测光夜的比例约为30%。冬季的典型消光为kV ~0.15等，色散很小。在夏季，灭绝有一个更广泛的价值观，虽然它没有达到在其他网站观察到的极端峰值。过去两年（2005- 2006年）的平均视景为~0.90”，夏季（~0.87”）小于冬季（~0.96”）。我们的结论是，在26年的操作后，卡拉尔阿尔托仍然是一个很好的天文网站，是一个自然的候选人，未来的大口径光学望远镜。
英文摘要：
We present a characterization of the main properties of the night-sky at the Calar Alto observatory for the time period between 2004 and 2007. We use optical spectrophotometric data, photometric calibrated images taken in moonless observing periods, together with the observing conditions regularly monitored at the observatory, such as atmospheric extinction and seeing. We derive, for the first time, the typical moonless night-sky optical spectrum for the observatory. The spectrum shows a strong contamination by different pollution lines, in particular from Mercury lines, which contribution to the sky-brightness in the different bands is of the order of ~0.09 mag, ~0.16 mag and ~0.10 mag in B, V and R respectively. The zenith-corrected values of the moonless night-sky surface brightness are 22.39, 22.86, 22.01, 21.36 and 19.25 mag arcsec^-2 in U, B, V, R and I, which indicates that Calar Alto is a particularly dark site for optical observations up to the I-band. The fraction of astronomical useful nights at the observatory is ~70%, with a ~30% of photometric nights. The typical extinction at the observatory is k_V~0.15 mag in the Winter season, with little dispersion. In summer the extinction has a wider range of values, although it does not reach the extreme peaks observed at other sites. The median seeing for the last two years (2005-6) was ~0.90", being smaller in the Summer (~0.87") than in the Winter (~0.96"). We conclude in general that after 26 years of operations Calar Alto is still a good astronomical site, being a natural candidate for future large aperture optical telescopes.
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