导引星

导引星是一个参考星，在天文学中，是用于保持望远镜准确对天体的跟踪，该物体在天空中的视运动主要是由于地球自转。

精确的望远镜指向和跟踪，对于获得良好的天文图像和天文摄影至关重要。但是，由于地球自转，天空相对于地球似乎永远处于恒定运动状态。虽然用肉眼观察时，这种运动似乎相对较慢，但即使是小型望远镜（英语：Small telescope）也能提供高放大倍率和更小的视野，使得这种运动在秒级的时间尺度上变得明显。

虽然太空望远镜没有安装在旋转的行星上，但它们仍然使用导引星，包括哈伯太空望远镜的导引星表中列出的那些天体。

通常使用计算机控制的电动机来使望远镜根据预先计算的指向模组（英语：Pointing model）与天空的视运动同步移动。但是，通常存在与模组相关的显著非零误差，只是对天空真实运动的近似值。

大多数现代的专业望远镜都使用导引星。自动导星（英语：Autoguider）指向位于被观察物体附近的一颗足够明亮的恒星，如果指向开始漂移，则可以检测到误差并纠正运动。当计算机应用校正时，这是最准确的，但业余望远镜通常只有手动校正（需要观察者在曝光期间连续用眼睛跟随恒星，这可能会是一个很长的时间）。

导引星也被用于调适光学。在这种应用中，恒星不是用来校正地球的自转，而是用来校正地球大气层中的湍流。通过测量观察到的导引星运动，并对主镜进行微小的扭曲，望远镜可以产生比没有调适光学元件时更清晰的图像。然而，只有大约1%的夜空足够接近天然导引星以使用调适光学，因此已经开发了各种制造人工激光导引星的方法，包括由劳伦斯利佛摩国家实验室开发并被加利福尼亚大学的Lick和Keck天文台使用的^[3]。

参考资料

^ GALACSI. eso.org. ESO. [2024-08-03]. （原始内容存档于2024-02-13）.
^ Announcement. GALACSI Adaptive Optics System Ready to be Mounted on the VLT. The VLT’s MUSE will soon be able to see even more clearly. eso.org. ESO. [2024-08-03]. （原始内容存档于2024-07-20）. GALACSI will rely on 4 sodium lasers launched from the centre piece of one of the Unit Telescopes of the VLT to produce “artificial stars”, known as guide stars. Sensors then follow the motion of these guide stars as the light from them flickers in the turbulent atmosphere. That allows a computer to calculate the correction that must be applied to the telescope’s deformable secondary mirror (itself a new addition to the VLT) to compensate for the atmospheric disturbance. In this way, extremely sharp images of the real celestial objects can be obtained.
^ Heller, Arnie. Science and Technology Review: Adaptive Optics Sharpen the View from Earth. Blur free imagereveal a wealth of astronomical detail. Lawrence Livermore National Laboratory. 2002-06-12 [2024-08-03]. （原始内容存档于2017-02-09）. The dye laser, similar to that pioneered at Livermore for its Atomic Vapor Laser Isotope Separation program, creates a glowing star of sodium atoms measuring less than 1 meter in diameter at an altitude of about 100 kilometers above Earth’s surface. This artificial reference can be created as close to the astronomical target as desired so that the light from the laser star and the observed object pass through the same small part of the atmosphere.

[1] GALACSI. eso.org. ESO. [2024-08-03]. （原始内容存档于2024-02-13）.

[2] Announcement. GALACSI Adaptive Optics System Ready to be Mounted on the VLT. The VLT’s MUSE will soon be able to see even more clearly. eso.org. ESO. [2024-08-03]. （原始内容存档于2024-07-20）. GALACSI will rely on 4 sodium lasers launched from the centre piece of one of the Unit Telescopes of the VLT to produce “artificial stars”, known as guide stars. Sensors then follow the motion of these guide stars as the light from them flickers in the turbulent atmosphere. That allows a computer to calculate the correction that must be applied to the telescope’s deformable secondary mirror (itself a new addition to the VLT) to compensate for the atmospheric disturbance. In this way, extremely sharp images of the real celestial objects can be obtained.

[3] Heller, Arnie. Science and Technology Review: Adaptive Optics Sharpen the View from Earth. Blur free imagereveal a wealth of astronomical detail. Lawrence Livermore National Laboratory. 2002-06-12 [2024-08-03]. （原始内容存档于2017-02-09）. The dye laser, similar to that pioneered at Livermore for its Atomic Vapor Laser Isotope Separation program, creates a glowing star of sodium atoms measuring less than 1 meter in diameter at an altitude of about 100 kilometers above Earth’s surface. This artificial reference can be created as close to the astronomical target as desired so that the light from the laser star and the observed object pass through the same small part of the atmosphere.

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