You may have noticed that the Moon has been showing a ghostly glow lately, where a subtle glow illuminates a normally unlit part of the moon’s surface. It’s a phenomenon called Earthshine, and it can be an amazing sight, not to mention a great opportunity for lunar photography.
In this article, we explain when you can see this lunar glow, what causes it, and why it’s named after one of the most famous polymaths of all time.
You can also make the most of bright nights this year at our full UK calendar month and astronomy for beginners guides.
When can I see Earthshine?
Weather permitting, you can see Earthshine tonight, 23 Mayafter sunset (8:56pm BST in London, 8:13pm EDT in New York City).
Earthshine is visible in the morning a few days before the new Moon, and in the evening a few days after the new Moon. You may have caught a glimpse of it before sunrise on May 17 during the waning crescent phase, but if you don’t want to drag yourself out of bed at that time, we have another chance during waxing crescent Moon phase.
Here are the next opportunities to see Earthshine:
- 23 May: 15.5 percent illuminate the waxing crescent Moon
“Look on the night of May 23, and you’ll see the crescent Moon between the bright planet Venus and the star Pollux, with the red planet Mars just to the left of the pair,” he advises. Dr. Darren Baskilllecturer in astronomy at the University of Sussex.
The phenomenon is most visible during the waxing or waning crescent phase, as the illuminated side of the Moon is thinner, allowing for a greater portion of the dark Moon to be illuminated by Earthshine.
It’s the perfect time of year to view, because during spring, the northern hemisphere is tilted toward the Sun, while at higher latitudes, lingering winter snow and ice still cover the ground. Snow and ice reflect more light than darker-colored vegetation and water (ie, snow and ice have a higher albedo), so we get a brighter Earthshine.
Although you might expect Earthshine to be brighter during the winter months when snow and ice cover it, the amount of light reaching the Arctic is significantly less, so Earthshine is less of an event during winter.
Bottom line: go out and see it while you still can!
What exactly is Earthshine?
Earthshine appears as a soft, subtle glow on the unlit, or ‘night’ side of the Moon during certain phases. This is when a delicate, but somehow ghostly, shape of the full Moon is located in the arc of the bright crescent Moon, and it is a beautiful sight for these early summer nights.
Also known as Da Vinci glow, the intensity of Earthshine may vary depending on certain factorssuch as atmospheric conditions, Earth’s reflectivity, and observer location.
Just be aware of the popular media saying that the ‘dark side of the Moon is visible’ because this is incorrect; the dark side of the Moon faces away from us.
As the Moon is locked, we can never see the dark side of the Moon from where we are on Earth. Instead, we will see the no light part.
What causes this?
Earthshine is also known as Da Vinci glow, ashen glow, or more romantically, ‘the old Moon in the new Moon’s arms’. It is caused by the sun’s rays reflecting off the Earth’s surface and then reflecting back to the Moon.
“Like all planets and moons, Earth doesn’t emit light — it just reflects sunlight,” Baskill explained.
“This reflected sunlight can be seen illuminating the darker side of the Moon for several days on either side of the new Moon, when the Moon appears as a crescent in the evening or morning sky.
“The crescent Moon is caused by bright sunlight shining directly on the Moon, while the darker side of the Moon is partially illuminated by Earthshine – sunlight reflecting off Earth to gently illuminate the Moon.”
Earthshine occurs during the phase of the lunar cycle when a thin crescent of the Moon is illuminated by directly sunlight – either in the waxing or waning phase.
As for the part of the Moon that is not lit by direct sunlight, this is the part we see as a ghostly glow. As we all know, light from the Sun reaches the Earth and shines on its surface. But it is not limited to lands, as it also includes clouds, oceans, and the atmosphere.
Some of this light is then scattered, scattered, and reflected back into space. A portion of this reflected light travels to the Moon, arriving at its unlit side, the lunar night side.
The Moon, despite having a non-reflective surface, reflects reflected sunlight from Earth. And this phenomenon, which results in a faint glow on the part of the Moon that has no light, provides a subtle illumination on the otherwise dark surface of the moon.
What affects it?
The appearance and intensity of Earthshine is influenced by several factors, including the Earth’s cloud cover, the composition of its atmosphere, and the angle of sunlight reflecting off our planet onto the Moon. These factors can cause slight variations in the brightness and color of Earthshine, making it different every time.
Earth’s atmosphere, for example, plays an important role in shaping the appearance of Earthshine. As light from the Sun passes through the atmosphere, it undergoes scattering and absorption, with different wavelengths being affected to different degrees. This atmospheric filtering influences the color and intensity of Earthshine, and this light is ultimately reflected back to the Moon.
Different ground covers will reflect different amounts of light; for example, the ground reflects about 10-25 percent, while clouds reflect about 50 percent of the light.
Why is it called the Da Vinci glow?
In the early 16th Century, the Renaissance polymath Leonardo da Vinci turned his thoughts to solving the puzzle of this strange, otherworldly glow. He made detailed drawings and sketches of the Moon, and while da Vinci did not coin the term himself, these observations led to its association with his name.
His notebooks contain a drawing depicting Earthshine, which is now celebrated in Codex Leicester, a compilation of Da Vinci’s scientific writings. Although you need patience if you want to read the manuscript yourself, as da Vinci recorded his observations in his characteristic mirror writing; back-to-front Italian.
What equipment do I need to see the Da Vinci glow?
Apart from the constant desire for clear skies, no special equipment is required. If you have them to hand, although not required, using binoculars or a telescope can help you pick out features you wouldn’t normally see on the Moon’s surface, and get a closer look at subtle variations in brightness .
You might even want to try sketching the Moon on dark paper with chalk, pastel, or pencil.
Will climate change affect our ability to see it?
Potentially. Researchers looking at the Earth’s albedo discovered that warming temperatures may result in less intense Earthshine.
As the oceans warmed, they found that fewer low clouds formed in the eastern Pacific Ocean, west of the Big Bear Solar Observatory in California where they were taking measurements. This reduction in cloud cover leads to a slight decrease in the Earth’s albedo (reflectiveness), which subsequently affects the intensity of the Da Vinci glow.
About our expert
Dr Darren Baskill is an outreach officer and lecturer in the department of physics and astronomy at the University of Sussex. He previously lectured at the Royal Observatory Greenwich, where he also initiated the annual Astronomy Photographer of the Year competition.