Ann wrote:I'm still a bit confused at the utterly non-blue appearance of the Earth in today's APOD. Take a look at the picture at left, showing the Earth as seen from space. There is a prominent yellow-gray hurricane in the foreground, but the limb of the Earth is blue. There is absolutely no hint of blue in today's APOD.
Is the limb of the Earth typically blue when seen from space? During what circumstances is it not blue?
Finally, is it possible that the emission of more and more pollutants into the Earth's atmosphere could make it less blue when seen from space?
Sun has likely set - no blues. Earth must be fainter than the daytime views (and subsequently look washed-out) to achieve that image. However, it is possible that a 21% illuminated moon is illuminating the earth at this time.
At 21:27UT on Aug 9th the ISS was approaching sunrise in a few minutes. If I interpreted the view direction to the Milky Way correctly, the sun would rise within, or close to, the camera FoV.
Thanks, and good point, alter-ego, but the moonlit Earth sky is actually blue, as can be seen in this picture
by Dario Giannobile. David Malin, the British-Australian astrophotographer, specifically pointed out in his book A View of the Universe
that the moonlit sky is blue. So it seems to me that if the Earth is illuminated by the Moon, even if it is only a 21% Moon, that should not preclude the limb of the Earth from looking blue.
Could it be that the Sun has set, there is negligible moonlight, and the cloud cover of the Earth is "lit from within", by light pollution? Would that make the limb of the Earth look non-blue?
You pointed out that sunrise is fast approaching in this image. Could the reddish tones of the atmosphere at right be the red sky of dawn