Earthshine
If you look closely at a crescent moon just after dark (for a waxing crescent) or just before dawn (for a waning crescent), you’ll notice the unlit part of the moon. While the brightly lit portion receives direct sunlight, the unlit part is illuminated by earthshine—light reflected off Earth.
Earthshine is the dim glow visible on the unlit part of a crescent moon, caused by sunlight reflected from Earth.
The brightness of earthshine varies throughout the year, as it primarily depends on Earth’s cloud cover. The cloudier the Earth, the brighter the earthshine.
Why is earthshine visible when the moon is a crescent?
Just as a full moon can illuminate the night side of Earth, a full Earth can illuminate the night side (the unlit part) of the moon.
When we look from Earth, we see the phases of the moon. Similarly, if we were on the moon, we would see the phases of Earth. However, the phases of the moon and Earth are opposite to each other.
So, when the moon appears as a slim crescent in our sky, a full Earth appears in the moon’s night sky. This full Earth is bright enough to faintly illuminate the night side (the unlit part) of the moon.
When will earthshine be visible next in 2025?
As the new moon falls on November 20, 2025, the next earthshine will be visible from November 23 to 26, 2025, on the unlit part of the waxing crescent moon. Look for it in the western sky after sunset, when the sky becomes dark.
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