Earthshine Mornings

What Is Earthshine?

Earthshine, also known as lunar glow, is a faint illumination that brightens the dark side of the Moon. This occurs when sunlight is reflected off the Earth’s surface and then bounces back onto the Moon.

Earthshine is also referred to as ashen glow, the old Moon in the new Moon’s arms, or the Da Vinci glow, in honor of Leonardo da Vinci, who first described this phenomenon in recorded history.

Best Times to See Earthshine

In 2024, the optimal period to observe earthshine falls a few days prior to and following the New Moons occurring on May 4 and May 5 (dates may differ based on the time zone).

Why Does it Happen?

The occurrence of earthshine is a result of sunlight bouncing off the Earth’s surface and casting light on the unilluminated part of the Moon’s surface.

Due to the double reflection of light, first off the Earth’s surface and then off the Moon’s surface, earthshine appears significantly fainter compared to the illuminated section of the Moon.

When this phenomenon takes place on the moons of other planets, it is referred to as planetshine.

Ability to Reflect Sunlight

Earthshine’s luminosity is impacted by the Moon’s albedo, which is a gauge of how much solar radiation a celestial body can bounce back. Albedo is quantified on a spectrum from 0 to 1. An entity with an albedo of 0 absorbs all sunlight and appears completely dark. Conversely, an object with an albedo of 1 reflects all sunlight that strikes it.

The Moon boasts an average albedo of 0.12, while the Earth’s average albedo stands at 0.3. This indicates that the Moon reflects roughly 12% of the sunlight it receives, whereas the Earth reflects around 30% of the sunlight that reaches its surface. Consequently, when viewed from the Moon, the Earth appears approximately 100 times brighter than a full Moon observed from Earth.