Have you ever seen the Moon rising over your town or city?It can appear very large when it is low on the horizon. Our moon goes through phases(月相)and it looks a little different every day. When the whole moon is lit up, it is called a full moon. When the Moon is entirely dark, it's a new moon. When there is only a thin edge of the circle shining, it's a crescent moon.
When a crescent moon is rising, we can occasionally see a unique event. When the Sun, the Earth, and the Moon are lined up just right, some of the sunlight that hits the Earth can be reflected onto the Moon. This causes most part of the Moon to give off a faint glow, while the rest of the Moon is brightly lit by the sunlight.
This phenomenon is named the Da Vinci glow. It was Leonardo da Vinci, a great artist, inventor and scientist, who explained it for the first time. Sometimes, it is also called "earthshine. "
When Da Vinci wrote about earthshine, he suggested that it might be caused by sunlight reflected from the Earth's oceans. He was almost completely correct, except for one detail: most of the reflected sunlight comes from the clouds in our atmosphere. The reflected light from the Earth is bright enough to light up the side of the Moon that isn't receiving direct sunlight.
The Da Vinci glow is not easy to see. Conditions need to be just right. Due to the angles of light, the Moon has to be very low on the horizon. The best time to see it will be in the days before and after the new moon. During these days, the lit-up edge of the crescent moon is at its thinnest stage. If you observe the Moon before sunrise or after sunset, it may be possible to witness the reflected light from the Earth. For the best experience, choose a location outdoors where there is not too much artificial light. You can use a telescope, but it's not necessary since the Moon will look just as impressive when viewed with the bare eye.
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