Earthshine
Earthshine is a beautiful dim glow visible on the unlit part of the moon.
The illuminated part of the moon is visible when sunlight reflects from the moon directly. However, the unlit part of the moon is visible when sunlight reflects from Earth and back onto the moon. So earthshine is earthlight shining on the night side of the moon.
Earthshine is visible a few days before and after the new moon, when the moon is in its crescent phase. Check out our daily moon guide to know the current moon phase.
Look in the eastern sky preceding sunrise (when the sky remains dark) on the unlit part of the waning crescent moon or in the western sky following sunset (when the sky becomes dark) on the unlit part of the waxing crescent moon to see earthshine.
You need no instruments, like a pair of binoculars or a telescope, to see earthshine. It is easily visible to the naked eye if your night sky is dark and clear.
Earthshine in 2024
When to see the next earthshine in 2024: The next earthshine will be visible from December 4 to December 6 in 2024 on the unlit part of the waxing crescent moon.
On December 4, the waxing crescent moon will be 11% illuminated, and the earthshine will be visible on the rest of the 89% unlit part of the moon.
On December 5, the waxing crescent moon will be 19% illuminated, and the earthshine will be visible on the rest of the 81% unlit part of the moon.
On December 6, the waxing crescent moon will be 28% illuminated, and the earthshine will be visible on the rest of the 72% unlit part of the moon.
Where to look to see the next earthshine in 2024: Look in the western sky around an hour after sunset on the unlit part of the waxing crescent moon.
Da Vinci glow
Earthshine is also known as Da Vinci glow because Leonardo da Vinci illustrated the phenomenon and explained its cause for the first time over 500 years ago. Visit here to see the sketch of Leonardo da Vinci.
Leonardo thought the unlit part of the moon shines when sunlight reflects from Earth’s oceans. However, nowadays we know that this is not entirely correct. In reality, 50% of the reflection comes from Earth’s clouds and only 10% from Earth’s oceans.
Best time of the year to see earthshine
The strength of earthshine varies throughout the year as the amount of light reflected from Earth depends on part of Earth and the cloud cover.
However, it is more intense in the summer (April to June) due to global warming.
Why do we see earthshine when the moon is in crescent phase?
We know that a full moon can illuminate (light up) the landscape of Earth at night. Similarly, a full Earth can illuminate the landscape of the moon at night.
Now, similar to the phases of the moon, our Earth also goes through phases, as seen from the moon, and the phases of the moon and Earth are complementary.
So a full Earth is seen from the lunar night sky when the moon looks crescent in our sky, and this full Earth is bright enough to faintly illuminate the darkened surface of the moon. It is very similar to a full moon, which illuminates the darkened surface of Earth.
So we see earthshine when Earth looks full from the moon’s perspective and the moon looks crescent from Earth’s perspective.
And we see bright moonlight when the moon looks full from Earth’s perspective and Earth looks slim crescent from the moon’s perspective.
References
Apparent magnitude of earthshine: a simple calculation
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