When moonlight passes through the Earth's atmosphere, it undergoes scattering and refraction. The atmosphere of the autumn night is clearer, and the moon will appear more bright, presenting a white Mid Autumn Festival that is more in line with its original appearance. Watching the moon is a romance handed down from generation to generation in China. Looking up at the night sky, the bright autumn moon adds a warm atmosphere to the festival of family reunion, giving people endless beauty and imagination. Autumn wind is clear, autumn moon is bright. In people's impression, the moon in autumn is particularly bright, especially on clear nights when a "white moon" hangs high in the night sky. In daily observations, we can also see a "yellow moon" or even a "red moon". Why is this? In fact, the moon itself does not emit light. It is seen by us through the reflection of sunlight, and its color is determined by the color of its own reflected light. What we usually refer to as' moonlight 'is the sunlight reflected by the moon. So the true appearance of the moon should be white like sunlight. However, when moonlight passes through the Earth's atmosphere, it undergoes scattering and refraction. Even in the night sky on the same day, the color of the moon varies with changes in altitude. When the moon rises above the horizon, it needs to pass through a thicker atmosphere. Gas molecules and dust will scatter shorter wavelengths of light, causing longer wavelengths of red and yellow light to reach the ground. Therefore, the moon will appear reddish or yellowish, presenting an "orange moon" or "yellow moon". When there is a high content of water vapor or dust in the air, this atmospheric scattering effect becomes more pronounced, leaving behind more of the longest wavelength red light, which gives rise to the 'red moon'. As the moon rises higher and higher, the atmospheric scattering effect weakens, and the moon gradually returns to its original shape. At this point, we will see a bright "white moon" in the sky. The bright moon in the sky "is exactly what it means. In addition to being influenced by the Earth's atmosphere, the difference between lunar mare and lunar lander also affects the appearance of the moon as we see it. Lunar mare refers to a low-lying area or plain on the surface of the moon, which is 1 to 4 kilometers lower than the average lunar water level. The Mare Imbrium used to be a huge impact crater, with its bottom covered by black basaltic lava, resulting in a flat terrain and a darker color. Although it is called 'sea', in fact, the lunar sea has no water at all. Some bright areas on the moon are called lunar land, also known as highlands. The different reflectivity of materials in these two regions allows for different shapes of shadows to appear on the moon, such as the imagination of "little rabbits" and "trees", which has led to the legend of Chang'e Yutu and Wu Gang's expedition to Guangxi being passed down for thousands of years. In autumn, the sky is clear and the cool autumn wind lowers the temperature and takes away a lot of moisture and dust from the air. Compared with other seasons' nights, the atmosphere on autumn nights is clearer and the moon appears brighter. It is worth mentioning that although the autumn moon is white, during special moments such as a total lunar eclipse, the moon becomes a true 'red moon'. Because at this moment, the originally bright full moon enters the shadow of the Earth, and only a small amount of red light in the sunlight can be refracted by the Earth's atmosphere and projected onto the moon hidden in the Earth's shadow, making the moon appear bright red. (Liao Xinshe) (Author: Wang Kechao, Science Popularization Supervisor of Zijinshan Observatory, Chinese Academy of Sciences)