Thread: Moon face visible during waning crescent

Yesterday, in Norway, during night time the whole moon face was visible during waning crescent. Approximatly 26,9% (ref. a internet moon calendar) of the moon was lighted by the sun - but still the whole moon was visible to human eye.

It is not the first time I have observed this, but it has gotten me wondering...
During the Apollo expeditions it was said that since there where little or no particles in the space round the moon, nor an atmosphere, the shady side of objects, obstacles, things or even your hand / body where completly dark / black. This caused some problems when they had to do things because they needed to illuminate that point directly, as no light where reflected / diffused.
Where there is no light on the moon, it is completly dark / black in opposite to the earth where it is always some light on the surface, even on the backside of the earth relativly to the sun.

My question is then, since the reason for why I could see the moon then, in my theory (so far), can not be particles that diffuses the light around the moon, what is it then? My first assumption must be that the earth, due to the position of the sun, perhaps must be the light source? I have not found any sources of information about this theme yet, but I have found articles on how much light you would need to light up the moon, which tells my logic sense that I might not have found the answer, or the only answer to the phenomenon yet.

I look forward to your elucidation of the theme.


Regards,
OAB

Originally Posted by oab

My question is then, since the reason for why I could see the moon then, in my theory (so far), can not be particles that diffuses the light around the moon, what is it then? My first assumption must be that the earth, due to the position of the sun, perhaps must be the light source?

Yes, you are absolutely right. Already Galileo Galilei in his early publication about his Moon observations in 1610 (Nuncius sidereus) described this phenomenon and gave the correct answer.

The less of the Moon illuminated by the sun is visible from Earth, the more of the Earth illuminated by the sun is facing the Moon. This means that the effect is stronger the smaller the Moon phase is. There are even annual changes, because the larger polar ice cap and the larger snow coverage of the northern land masses during the northern winter produces a higher albedo than in summer.

also known as "earthshine"

Thank you very much for your information on the topic, references and the link to wikipedia. Collective information sources, such as this forum specialized on science, is more powerfull than anything I can imagine... Such collective sources will definitively play a important role in the future for problem solving and creation.

It won't be my last question on this forum - thank you very much :-D

Best regards from Norway!
OAB