According to the Guangzhou Wuyang Astronomical Museum, the night of December 26th to the early morning of the 27th will witness the lAst full moon in 2023. In the area around 28 degrees north latitude in China, a round full moon can be observed in the center of the sky, presenting a rare phenomenon of "no shadow under the bright moon". This special celestial event occurs approximately once every 18 years.

According to experts of the Guangzhou Wuyang Astronomical Museum, at 8:33 am on December 27th, the moon, the earth, and the sun will align in a nearly straight line, and the moon appears to be the fullest from the earth. At 5:51 am on December 27th, the moon reaches its highest point at a latitude of 28 degrees 8.7 minutes north, which is the farthest position from the equator in 18 years (the farthest angular distance). Therefore, on thAt day, in locations approximately at 28 degrees north latitude in China, the full moon will shine exactly on one's top, leaving no shadow on the ground.

It is expected that the phenomenon of"no shadow"willappearin some areas of Zhejiang, Fujian, Jiangxi, Hunan, Guizhou, Yunnan, Sichuan, and Tibet Autonomous Region, which can be observed by simply putting a mineral water bottle on the ground.

What's the reason for thisphenomenon? According to the experts of the museum, Astronomers call the apparent trajectory of the sun in the sky as the ecliptic and the apparent trajectory of the moon as the moon's path. These two paths have an average of 5 degrees and 9 minutes of intersection angle. Every year on the summer solstice (around June 21st or 22nd), when the sun runs to the sky above the Tropic of Cancer at the farthest angle distance from the equator (23 degrees 26 minutes north latitude), the moon runs to the northernmost and farthest position from the equator at the angular distance (28 degrees 35 minutes). The period of this astronomical cycle is 18.61 years, which is the reason it needs 18 years to witness such a full moon near 28 degrees north latitude.

Although such a phenomenon will not appear in Guangzhou on December 27th, the full moon will be higher than usual in Guangzhou. It is estimated that at that time, the moon will have an altitude of 85 degrees above the horizon in Guangzhou in the due north, like a compass.

Source:Yangcheng Evening News

2023年最后一次满月，“十八年”难遇

从广州市五羊天象馆获悉，12月26日夜间至27日凌晨，将是2023年最后一次满月出现的日子。在我国北纬大约28度的地区，可观赏到圆圆的满月位于苍天的中央，呈现“头上有明月，脚下无暗影”的罕见天象。这种特殊的天象，大约18年才出现一次。

五羊天象馆相关专家介绍，12月27日8时33分，月亮、地球和太阳排成近似一条直线，此时从地球角度看月亮最圆；在12月27日5时51分，月亮运行到北纬28度8.7分的上空，这是十八年来月亮运行到距离赤道最远的位置（角度距离最远）。因而当天我国北纬大约28度的地点，可以见到满月当头的奇特天象。

预计届时浙江省、福建省、江西省、湖南省、贵州省、云南省、四川省和西藏自治区部分地区可见“立竿无影”，公众在“月上中天”时将矿泉水瓶竖立在地面上时，便可观察到月光下“立竿不见影”的景象。

为何会出现上述有趣景象？五羊天象馆相关专家介绍，天文学家把太阳在天空中运行的视轨迹称为黄道，把月球在天空中运行的视轨迹称为白道，而黄道与白道有一个平均值为5度9分的交角；每年“夏至”，太阳运行到北回归线的上空（与赤道角度距离最远），即北纬23度26分的位置，此时月亮运行到距离赤道最北最远的位置（角度距离），即28度35分。这一天文周期的时间长度为18.61年，这也是北纬28度附近大约十八年可遇见一次“立杆无影”满月奇观的原因。

五羊天象馆相关专家介绍，广州届时虽看不到“立竿无影”的满月，但预计12月27日“月上中天”时，广州市民可看到相比平日所处位置更“高”的满月。预计上述时间月亮在广州地区地平高度为85度，月亮位于正北方向，成为名副其实的“指北针”。

文｜记者 孙牧 梁怿韬 通讯员 李建基
译｜白心怡