On: July 8 99% of the world’s population in sunlight s...

[ninju]

I believe you are referring to the Valeriepieris circle

https://en.wikipedia.org/wiki/Valeriepieris_circle#/media/Fi...

https://en.wikipedia.org/wiki/Valeriepieris_circle

[corrral → ninju]

Yep, that's the one. Ballpark 7% of the Earth's surface, or 15% of the land-surface area (guesstimate based on the whole circle being about 22% of the land surface area—but much of the circle is over water). Over 50% of the population.

[Beldin → corrral]

One of the claims of the circle was that over half of it was water. So then your guesstimate can be lowered to less than 11% of land surface area.