Earthshine: Why Is the “Dark Side” Of The Moon Sometimes Glowing — And How To Catch It This April

Have you ever looked up at the Moon and noticed a sophisticated, slim crescent, while the rest of the Moon remains faintly visible, even though it’s not a full Moon? This marvellous phenomenon is known as Earthshine.

From Earth, it appears as though the new Moon is embracing the old Moon, so sometimes it’s called “the old Moon in the new Moon’s arms”.

So, what is Earthshine? Let’s explore.

What Is The Meaning Of Earthshine?

Earthshine refers to the dull illumination of the dark part of the Moon caused by sunlight reflecting off Earth’s surface and atmosphere and back to the Moon. 

The light from the Sun reaches the Earth and then bounces back to the Moon. As a result, the unlit part of the Moon is faintly visible.

For a few days before and after the New Moon, when the Moon is a thin crescent, this doubly reflected earthshine is powerful enough to make the whole Moon visible.

Mysterious Da Vinci Glow

In the 16th century, Leonardo da Vinci sketched and explained for the first time this phenomenon. The painter and scientist thought that the illumination is caused by reflections from the oceans on the Earth. However, later scientists discovered that clouds play a much more important role in this process.

Still, sometimes the scientists call the Earthshine the Da Vinci Glow due to the fact that he was the first person in recorded history to pay scientific attention to this effect.

What Causes The Ghostly Glow Of The Moon?

To understand the reasons behind the Earthshine, we need to keep in mind that the Earth has phases, as well as the Moon. These phases are the same, but complementary – opposite to each other. Meaning that when we see the Moon in its new phase, the Earth will be full from the Moon surface, and vice versa.

Since Earth is four times larger than the Moon, in its full phase the sunlight illuminates it almost completely. During this phase, Earth’s light is so intense that it illuminates the Moon and reflects back to our planet. As a result, we can see the lunar dark part lit up by the Earth’s shine – this is Earthshine.

Earthshine is most visible when the Earth is full and the Moon is new – a thin crescent. 

The surface of the Earth is quite reflective – it reflects about 30% of all the sunlight that hits its surface. As a result, from the Moon, Earth would appear around 100 times brighter than a full Moon looks to us!

Here Is How The Earthshine Works Step By Step:

• Sunlight reaches Earth 
• Earth reflects the light towards the Moon – the clouds or snow cover enhance the effect
• The Moon’s dark side is illuminated, glowing faintly from Earth’s reflected light
• The Moon reflects this light back to Earth – we see this as a ghostly illumination of the dark part of the Moon.

What Is The Difference Between Earthlight And Earthshine? 

Though closely related, Earthlight and Earthshine aren’t quite the same thing in astronomy.

Earth’s surface and clouds reflect light, creating a general illumination of space – earthlight. It is similar to how the Sun’s light illuminates the Moon or other celestial bodies.

Earthshine, on the other hand, is a specific type of earthlight – reflected sunlight from Earth to the Moon (and then back to Earth).

In other words, Earthshine is a visible effect of Earthlight on the Moon.

What Is The Difference Between Moonlight And Earthshine?

The difference between moonlight and Earthshine lies in their sources and how they illuminate objects.

Moonlight is sunlight reflected off the Moon’s surface and shining down on our planet. It’s the familiar glow we see when the Moon lights up the night.

While Earthshine is a bit more interesting and complicated process – it’s sunlight that first reflects off Earth, then reaches the Moon, illuminating its darker, unlit portion, and gets back to our planet. 

In short, moonlight is the Moon shining on Earth, while Earthshine is Earth shining on the Moon and back to us – a wonderful cosmic reflection.

Best Time To See Earthshine In 2025

The best time to spot Earthshine is a few days before and after a New Moon. Better be ready right after sunset or before sunrise. The Earthshine is more intense in April and May, so it’s the perfect time to observe it.

This year, the best time to see Earthshine is a few days around the New Moons on 27th April and 27th May. So keep in mind and don’t miss this beautiful effect!

Look for the best astronomical events you can witness in April 2025.