Earthshine – the dim glow visible on the unlit part of a slim crescent moon – is the reflection of Earth’s light on the moon.
It is visible between two to five days before and after a new moon, when the moon is in its crescent phase.
Earthshine in March 2025
When to see: The new moon will fall on March 29, 2025. So the earthshine will be visible from March 24 to 26, 2025 – on the unlit part of the waning crescent moon.
Where to look: Look in the eastern sky around an hour before sunrise for Earthshine.
Moon illumination: On March 24, the waning crescent moon will be 29% illuminated, and the earthshine will be visible on the rest of the 71% unlit part of the moon.
On March 25, the waning crescent moon will be 20% illuminated, and the earthshine will be visible on the rest of the 80% unlit part of the moon.
On March 26, the waning crescent moon will be 12% illuminated, and the earthshine will be visible on the rest of the 88% unlit part of the moon.
Optical aid requirements: Earthshine can be seen without optical aid. 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.
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.
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.
References
Apparent magnitude of earthshine: a simple calculation
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