月行迹

2020 May 7

Analemma of the Moon
Image Credit & Copyright: Gyorgy Soponyai

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. To create this composite image of a lunar analemma, astronomer Gyorgy Soponyai chose a lunar month from March 26 to April 18 with a good stretch of weather and a site close to home near Mogyorod, Hungary. Crescent lunar phases too thin and faint to capture around the New Moon are missing though. Facing southwest, the lights of Budapest are in the distance of the base image taken on March 27.

Tomorrow’s picture: pixels in space

月行迹
图像提供和版权：Gyorgy Soponyai

说明：较常见的8字形日行迹曲线，呈现太阳在一年之中，每天在相同的时间点于某地点天空中位置的变化。不过要拍摄月行迹，密诀是要知道每天延迟的时间。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，因为月亮自转轴倾斜和轨道椭圆造成的移位，月亮就会曳出和日行迹很像的行迹。 为了要组合出这幅月行迹影像，天文学家Gyorgy Soponyai选择的日期是天气上佳的3月26日（初三）到4月18日（二十六）之间，地点则是离家不远的匈牙利. 莫焦罗德村附近。影像中，新月前后数晚的月牙过于纤细难以记录。此外，拍照时面向西南，在摄于3月27日的底图里，可见到远方布达佩斯市的灯火。

明日的图片：pixels in space