月の欠けた部分がうっすら見える

　今朝５時４０分頃、南東の空に、月齢２７．３の「下弦の月」が出てました。快晴のためはっきり見え、すぐにカメラに収めました。ご存じの通り、１１月は太陽暦【現行歴】と太陰太陽暦【旧暦】の日付が同じでしたが、実は１２月も太陽暦と太陰太陽暦の日付が一致してます。このため、１２月３日は西南の空に三日月が出て、１２月１５日は十五夜です。

　ところで、今朝の細く欠けた月をよく観察すると、写真の通り、欠けた部分がうっすらと見えてます。この部分に太陽の光が当たることはないのに、何故うっすら見えるのでしょう？

　これは、地球に当たった太陽光が反射して月面をうっすら照らしています。これは「地球照」と呼ばれる現象です。私の想像では、日本で見る場合は、太平洋に映る太陽光が月を照らしていると想われます。

　私たちが住む地球でも、満月の夜には、月は光を発してないのに月の光にかなり照らし出されます。同様に、月面も明るい地球に照らされることになります。特に、地球から見て三日月や新月に近く月の表面が大きく欠けている状態のとき、月から見る地球は満月のように明るいことから、その光に照らされることになります。月が大きく欠けている時ほど「地球照」は良く見えます。

Dear my overseas friends who like both of nature and great music

　The simultaneous interpretation for your understanding will be done after my radio gymnastics held in the nearby park and breakfast in Japan time.

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　At around 5:40 this morning, a waning moon with the phase of 27.3 appeared in the southeastern sky. It was a clear dawn, so I could see it clearly so that I quickly captured it on camera. As you know, the solar calendar [current calendar] and the lunisolar calendar [old calendar] have the same dates in November, but in fact, the solar calendar and the lunisolar calendar also have the same dates in the next December. For this reason, the waxing moon of the phase of 3 appeared in the southwestern sky on December 3rd, and December 15th is the fifteenth night of full moon.

　By the way, if I looked closely at the waning moon this morning, I could see that the crescent part is faintly visible, as in the photo. Why is it faintly visible in this part of the surface of the moon even though the sunlight does not shine on this part?

　This is because the sunlight hitting the Earth is reflected and faintly illuminates the surface of the moon. This is a phenomenon called "earthshine." In my imagination, when viewed it from Japan, the sunlight reflected on the Pacific Ocean is illuminating the moon.

　Even on Earth where we live, on nights of a full moon, the moon is illuminated by moonlight, even though the moon does not emit any light. Similarly, the surface of the moon is also illuminated by the bright Earth. In particular, when the moon is close to a waning crescent or new moon, the Earth seen from the moon appears as bright as a full moon. The more the moon is missing, the better the "earthshine" is visible.

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