page_title: Planetshine
section_title: Earthshine
hierarchical_section_title: Planetshine / Earthshine
caption_attribution_description: English: Conjunction of Venus and the Moon, illuminated by Earthshine.
context_page_description: Planetshine is the dim illumination, by sunlight reflected from a planet, of all or part of the otherwise dark side of any moon orbiting the body. Planetlight is the diffuse reflection of sunlight from a planet, whose albedo can be measured.
  The most observed and familiar example of planetshine is earthshine on the Moon, which is most visible from the night side of Earth when the lunar phase is crescent or nearly new, without the atmospheric brightness of the daytime sky. Typically, this results in the dark side of the Moon being bathed in a faint light.
  Planetshine has also been observed elsewhere in the Solar System. In particular, the Cassini space probe used Saturn's shine to image portions of the planet's moons, even when they do not reflect direct sunlight.
context_section_description: Earthshine is visible earthlight reflected from the Moon's night side. It is also known as the Moon's ashen glow or as "the new Moon with the old Moon in her arm".
  Earthshine is most readily visible from a few nights before until a few nights after a new moon, during the (waxing or waning) crescent phase. When the lunar phase is new as viewed from Earth, Earth would appear nearly fully sunlit from the Moon. Sunlight is reflected from Earth to the night side of the Moon. The night side appears to glow faintly, and the entire disk of the Moon is dimly illuminated.
  Leonardo da Vinci explained the phenomenon in the early 16th century when he realized that both Earth and the Moon reflect sunlight at the same time. Light is reflected from Earth to the Moon and back to Earth as earthshine.
  Earthshine is used to help determine the current albedo of Earth. The data are used to analyze global cloud cover, a climate factor. Oceans reflect the least amount of light, roughly 10%. Land reflects 10–25% of sunlight, and clouds reflect around 50%. Thus, the part of Earth where it is daytime and from where the Moon is visible determines how bright the earthshine on the Moon appears at any given time.
  Studies of earthshine can be used to show how the Earth's cloud cover varies over time.  Preliminary results show a 6.5% dip in cloud cover between 1985 and 1997 and a corresponding increase between 1997 and 2003. This has implications for climate research, especially with regards to global warming. All clouds contribute to an increased albedo, however some clouds have a net warming effect because they trap more heat than they reflect, while others have a net cooling effect because their increased albedo reflects more radiation than they trap heat. So while the Earth's albedo is measurably increasing, the uncertainty over the amount of heat trapped means the overall effect on global temperature remains unclear.
caption: Earthshine reflected from the Moon during conjunction with Venus (left)
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