Earthshine
Earthshine is the dim glow visible on the unlit part of the moon. It is the reflection of Earth’s light on the moon.
It is visible for a few days before and after a new moon, when the moon is in its crescent phase.
Why do we see earthshine?
We see earthshine when sunlight is reflected twice – first from Earth’s surface and then this Earth’s light from the moon’s surface. This light is much dimmer than the lit portion of the moon because the lit portion of the moon reflects sunlight directly.
Why do we see earthshine when the moon is in crescent phase?
Just as a full moon can illuminate the night side of Earth, a full Earth can illuminate the night side (dark side) of the moon.
When we look from Earth, we see the phases of the moon. Similarly, if we look from the moon, we can 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 (dark side) of the moon.
When to see the next earthshine in 2025?
As the new moon will fall on May 27, 2025, the next earthshine will be visible from May 22 to 24, 2025 – on the unlit part of the waning crescent moon. Look for them in the eastern sky around an hour before sunrise.
On May 22, the waning crescent moon will be 28% illuminated, and the earthshine will be visible on the rest of the 72% unlit part of the moon.
On May 23, the waning crescent moon will be 18% illuminated, and the earthshine will be visible on the rest of the 82% unlit part of the moon.
On May 24, the waning crescent moon will be 10% illuminated, and the earthshine will be visible on the rest of the 90% unlit part of the moon.
Can earthshine be seen with the naked eye?
Earthshine can be seen with the naked eye. However, its strength varies as the amount of light reflected from Earth depends on part of Earth and the cloud cover. You can use a pair of binoculars or a telescope for better visibility.
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