Why does the unlit portion of the moon blend into the sky?

[llivinglarge]

Whenever I see the moon rise early in the afternoon, the unlit portion seems to blend into the blue sky.

Shouldn't that portion be opaque or even have a faint outline?

 

[nimbus]

What is the blue sky, and what is the black of space, and why would the moon's unlit area be any different from the rest of space as seen thru our "blue" air?

 

[MeteorWayne]

Yes, the blue sky is right above is, and the unlit portion of the moon (~ 250,000 miles away) is almost (but not quite) as black as the space behind it. Actually, the unlit portion is lit up a little by reflected earthshine, but not enough to notice in the daytime. You can however see it on a dark clear night.

 

[kelvinzero]

I noticed that just recently. It must be fairly well lit on the nearside during a lunar night. The earth is always there and always at least a half crescent when the sun is below the horizon.

 

[CalliArcale]

Yeah, it's gotta be pretty bright at night on the nearside, especially when the Earth is full. Earthshine is very beautiful, isn't it?

 

[nimbus]

 

[SpaceTas]

The sky in daytime is lit up by scattered light from sun. So this scattered light is coming from in front of the Moon, reducing the contrast between the Moon and the sky. Through a telescope you'll notice than even the lit part of the moon looks washed out when observed in daylight.

It is like trying to see details of a distant mountain range through haze or through fog, or through smeary/misted glasses.