Matthew Chin Blog: 2021年香港元朗月行跡 Lunar Analemma, in Yuen Long, Hong Kong

2021年香港元朗月行跡 Lunar Analemma, in Yuen Long, Hong Kong

Shooting Period 拍攝日期: 2021/5/21 - 2021/6/17 (辛丑年農曆四月初十日至五月初八日)

Many years are passed, and finally I done that in 2021. Lunar analemma idea occurred actually when I shooted Sun analemma in 2014.

Not the same with Sun analemma, which I took in 2014, Sun analemma is taken on same time in days over the year.

We can photograph the Moon 50 minutes and 29 seconds (1.035028 days) later on successive days, to capture an figure-8 curve in 27 days. This is the Lunar analemma. It will be a bit different in shape in every month, at east or west side and in different countries on the Earth.

Sidereal month is the time it takes the Moon orbits the Earth to a similar position with 27.321 days. 2021/5/26 is total lunar eclipse, I can see the red moon.

The weather condition in Hong Kong is not optimistic, to watch the moon everyday in a month become fairly impossible, so moon is missing in certain days, (new moon is not count as it is invisible). And moon is shooted nearest possible in cloudy or rainy days in a daily basis.

Final photo is a cumulative of specific time's moons, the figure-8 analemma curve is still able to see. New moon days are on upper left side while full moon days are on bottom right side on the photo. Ground view is chosen in my Yuen Long residence estate. It needs around 60*40 degree space, facing east and southeast side, because I shoot moon rising at the east.

( Camera: Nikon D750 with 27mm and 300mm lens, no guiding. Photos are taken with various exposures. )

Epilogue:

Typhoon signal No.1 is hoisted by Hong Kong Observatory on June 11 to 12. Pray to the heaven, result is not good enough, but I just get it done. I think of Su Shi’s "When is the night without moon? Where is there no bamboo and cypress?" It is pity that Hong Kong will have "When is the night without moon?", so thing should be cherished.

Chinese follows. 中文隨後

2014年拍過日行跡後已有拍攝月行跡的念頭，多年已過去，直到今年才能成事。

和拍攝日行跡不一樣，日行跡在一年中的不同日子固定時間拍攝，而月亮需要在一個農曆月內每天延時50分29秒 (1.035028日) 拍攝27天才可捕捉到月行跡。月行跡8字的形狀每月會有少許差異，在地球上的不同國家，向東拍月昇，或向西拍月落也會有差異。

恆星月是月球繞地球公轉 360°的時間，為27.321天。2021/5/26日是月全食，我看到紅月亮。

香港的天氣比較糟，一個月要天天見到月亮變得不太可能，(不計算初一，因為初一月亮是看不見的)，圖中有月亮缺失的日子；我堅持在每天拍攝，如果多雲/有雨，會用最近時間拍到的月亮。

最後圖片將特定時間的月亮叠合而成，8字月行跡仍可以看到，靠在相片左上方是新月前後，右下方是滿月的前後日子。地景是我元朗居住的屋苑，向東及東南方拍攝，需要有 60*40度左右的空間範圍，因為我是拍東昇的月亮。

( 相機: 尼康 D750 配備 27毫米和 300毫米鏡頭，無引導。照片用不同的曝光拍攝。 )

後記：

六月11-12日香港天文台掛起一號颱風訊號，望天打卦的日子並不理想，但我總算完成。想起蘇軾《記承天寺夜遊》「何夜無月？何處無竹柏？」的美景當前，追了一個月的月亮，香港是有「何夜無月」之嘆，所以，一切應該要珍惜。

Reference materials 參考資料

Time calculator:

https://www.calculator.net/time-calculator.html