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chornedsnorkack
2014-May-04, 01:13 PM
A general estimate of scattered skylight by day is 1/9 direct sunlight.

I found an account of large phase completely eclipse which estimated the illumination from scattered light near horizon as 100 times the light of Moon, or about 1/5000 Sunlight. Which also means about 1/500 the scattered light of fully illuminated sky. The corona of a totally eclipsed Sun was half the brightness of full Moon.

Now, from the centre of totality, partially eclipsed sky is less than 150 km away. Whereas uneclipsed sky illuminated by full sunlight is 3500 km away, far below horizon.

Thus an observer outside but near the edge or totality, or in antumbra, should see locally scattered skylight plus near horizon light from slightly less eclipsed but still large phase eclipsed sky.

At which phase of eclipse does the contrast between direct sunlight and scattered skylight start to decrease noticeably?

Hornblower
2014-May-04, 05:43 PM
I would expect the ratio of skylight to the Sun to remain virtually constant until just before totality, when the last sliver of the Sun is rapidly shrinking but a lot of skylight is still coming in from brightly lighted areas well outside the umbra.

chornedsnorkack
2014-May-04, 07:48 PM
This:
http://www.strickling.net/tse2009.htm
reports as little at 4 lux, and less than that on other eclipses:
http://www.strickling.net/sofi_eng.htm