土耳其上空的双月行迹

2022年10月10日

A Double Lunar Analemma over Turkey
Image Credit & Copyright: Betul Turksoy

Explanation: An analemma is that figure-8 curve you get when you mark the position of the Sun at the same time each day for one year. But the trick to imaging an analemma of the Moon is to wait bit longer. On average the Moon returns to the same position in the sky about 50 minutes and 29 seconds later each day. So photograph the Moon 50 minutes 29 seconds later on successive days. Over one lunation or lunar month it will trace out an analemma-like curve as the Moon’s actual position wanders due to its tilted and elliptical orbit. Since the featured image was taken over two months, it actually shows a double lunar analemma. Crescent lunar phases too thin and faint to capture around the New moon are missing. The two months the persistent astrophotographer chose were during a good stretch of weather during July and August, and the location was Kayseri, Turkey

Tomorrow’s picture: open space

土耳其上空的双月行迹
影像提供与版权: Betul Turksoy

说明: 较常见的8字形日行迹曲线，呈现太阳在一年之中，每天在相同的时间于某地天空中位置的变化。不过要拍摄月行迹，密诀是要知道每天拍照得延迟多久。平均来说，月亮回到相同位置的时间，要比前一天约晚50分29秒。所以每天晚50分29秒拍摄月亮，经过一个月相周期（朔望月）后，因为月亮的自转轴倾斜和椭圆轨道会造成移位，月亮就会曳出和日行迹很像的行迹。因为拍摄这幅主题影像的期间长达2个月，所以它呈现了2组月行迹。在影像中，新月前后的蛾眉月相纤细月盘太昏暗，所以难以拍摄而付之阙如。这位坚忍不懈的天文摄影者，选在土耳其开塞利市七、八这2个月的一段好天气期间进行这项摄影工作。

明日的图片: open space