The world can be divided into two hemispheres in several ways, Eastern-Western and Northern-Southern being the most well known. But the next best known is the somewhat hazy Land Hemisphere vs the Water or Sea Hemisphere.
When adjusted just right, the great circle boundary between these hemispheres divides the earth between a hemisphere that has 80% of the earth's land and a hemisphere that has only the remaining 20% of the earth's land.
Of course on a temporary basis there's a daylit hemisphere and a hemisphere that's in night (or at least twilight, with the sun down but near the horizon).
At what time on what day of the year, is the daylit portion of the earth most nearly coincident with the land hemisphere?
I would hazard: 11:24 UT on 6/21
Google Earth Pro is a pretty amazing app and is useful here. It makes the Water Hemisphere rather evident. The water world has a mid-longitude halfway between the Australian east coast (154 E) and the Californian west coast (124 W), which comes out to a long. of 170 W. Claiming a central latitude for this hemisphere becomes more subjective as one attempts to keep both Antarctica and land masses around the Bering Sea over the limb (the horizon). I wanted to exclude the latter more, so I chose a southern center for sea world. The opposite hemisphere is lit the most at high latitudes on the summer solstice (June 21).
The other side of long. 170 W is long. 10 E. The Google Earth Daylight Tool shows (23 N, 10 E) as the subsolar point on the solstice at 11:24 UT.
Edited on June 6, 2023, 3:55 pm
a possible solution
