Earthlight (astronomy)

This article is about light reflected by Earth. For light generated in Earth's atmosphere, see Airglow.
The night side of the moon, illuminated by earthshine, becomes visible next to the narrow crescent (11 percent, age of the moon = 3.3 days) with ash-grey moonlight. Image taken 20° over the western evening sky shortly after the equinox in spring with a particularly steep ecliptic as seen from Berlin. On the left, the star Omicron Arietis (37 Ari, 6,2m) in the constellation Aries.
During the crescent phase, the darker side of the Moon reflects indirect sunlight, reflected from Earth, while the other side reflects direct sunlight.
An 80 mm shot of a crescent Moon with a 10-second exposure, revealing earthshine. The green ghost image was caused by a UV filter on the lens.

Earthlight is the diffuse reflection of sunlight reflected from Earth's surface and clouds. Earthshine (an example of planetshine), also known as the Moon's ashen glow, is the dim illumination of the otherwise unilluminated portion of the Moon by this indirect sunlight. Earthlight on the Moon during the waxing crescent is called "the old Moon in the new Moon's arms",[1] while that during the waning crescent is called "the new Moon in the old Moon's arms".[2]

  1. ^ Nemiroff, Robert; Bonnell, Jerry (20 January 2018). "Old Moon in the New Moon's Arms". Astronomy Picture of the Day. NASA. Archived from the original on 17 June 2019. Retrieved 11 January 2020.
  2. ^ Nemiroff, Robert; Bonnell, Jerry (24 March 2012). "The New Moon in the Old Moon's Arms". Astronomy Picture of the Day. NASA. Archived from the original on 3 September 2019. Retrieved 11 January 2020.