As
@exchemist noted, because London is north of the Tropic of Cancer and Capetown south of the Tropic of Capricorn, the sun is never directly overhead in either place at any tie, that is, a vertical pole will always cast a shadow.
"The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun to its maximum extent."
Read about the famous experiment the ancient Greek Eratosthenes performed to estimate the size of the earth. When the sun was directly overhead in Syene, it cast no shadow (and illuminated a well), whereas in Alexandria at the same time, about 500 miles away. it did cast a shadow. Trigonometry allows one to determine the angle called alpha below, and from that, the approximate dimensions of the earth.
Do you think that that would be possible on a flat earth?
The top picture is not from 100,000 feet. That's approximately how the earth looks from the International Space Station, and I'll bet that that is where it was shot from. This is about 250 miles up.
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This is incoherent. Heliocentrism does not suggest that objects orbiting the sun are in unison, whatever that means. They mostly travel in the same plane and in the same direction, but the planes of the orbits aren't the same just as the plane of the moons orbit is not the same as the plane of the earths orbit around the sun, the shapes of the orbits have varying eccentricity, and the velocity of planetary orbits vary from one another, which is why earth and mars are at times on the same side of the sun making mars larger and brighter than when the two are on opposite sides of the sun.
Nothing about the velocity of the ISS tells us that the earth is flat.
No, not everybody thinks that the sun is directly overhead at noon.
Nor do they think that it is directly overhead in either of those places ever, much less simultaneously
I believe Cape Town (GMT + 2) is TWO hours AHEAD of London (GMC + 0), although during the summer, I believe only London observes daylight savings time (BST = British Summer Time = GMC + 1), at which time the clocks might be an hour apart, but what clocks show has nothing to do with the location of the sun in the two places at the same time. The sun still rises 120 minutes earlier in one than the other.
It's not the case.
Perhaps you need to be a bit more careful about your information sources.