What is Earthshine and when is the next one?

What is Earthshine?

A slim crescent moon with Earthshine — A slim crescent moon with earthshine. (Image credit: NASA/JPL-Caltech)

We see the illuminated part of the moon when sunlight reflects from the moon directly and reaches us.

However, sometimes the darkened part (unlit part) of the moon is seen when sunlight reflects twice. First, sunlight reflects from the earth, and then this earthlight reflects from the moon and back to our eyes. As a result, we see a faint, beautiful glow on the darkened part of the moon, called earthshine.

Earthshine is visible a few days before and after the new moon, when the moon is in its crescent 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 noticeable with unaided eyes if the night sky is dark and clear.

Earthshine is also known as Da Vinci glow because Leonardo da Vinci explained this phenomenon for the first time in the 16th century.

When is the next earthshine in 2024?

As the new moon falls on November 1 at 12:47 UTC, the next earthshine will be visible on the unlit part of the thin waning crescent moon from October 26 to October 30, 2024 (roughly). Check out our daily moon guide to know the current moon phase.

Best time of the year to see the earthshine

Earthshine is best visible in summer (April to June) because our earth reflects more sunlight in summer than any other time of the year.

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 the 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 earth and the moon are complementary.

During Earthshine, the earth looks nearly full from the moon when the moon looks slim crescent from the Earth — During earthshine, the earth looks nearly full from the moon, while the moon looks crescent from the earth. (Image credit: NASA/JPL-Caltech)

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 the earth.

So we see earthshine when the earth looks full from the moon’s perspective and the moon looks crescent from the earth’s perspective.

And we see bright moonlight when the moon looks full from the earth’s perspective and the earth looks slim crescent from the moon’s perspective.

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