The secretary general and US president looked questioningly at him.

“We’re looking at the sky from the other side of the Earth,” he said.

The US president yelped, but then restrained himself and said in a voice even lower than before, “You’ve got to be kidding.”

“Look, what’s that?” the secretary general said, pointing at the sky with a hand raised only to eye level so as not to alarm the others.

“The moon, of course,” the US president said after a brief glance overhead. But when the Chinese president slowly shook his head, he looked up a second time and was less certain. At first, the semicircular shape in the sky looked like the moon in first quarter, but it was bluish, as if a scrap of daytime sky had gotten stuck. The US president looked more closely at the blue semicircle. He held out a finger and measured the blue moon against it. “It’s growing.”

The three politicians stared up at the sky, not caring anymore if they’d startle the others. The heads of state in the surrounding seats noticed their movements, and more people looked upward. The orchestra on the outdoor stage abruptly stopped its warm-up.

By now, it was clear that the blue semicircle was not the moon, because its diameter had grown to twice that, and its darkness-shrouded other half was now visible in dim blue. In its brighter half, details could be made out; its surface was not a uniform blue but had patches of brown.

“God! Isn’t that North America?” someone shouted. They were right. You could distinguish the familiar shape of the continent, which lay smack on the border between the light and dark halves. (It may have occurred to someone that was the very same position they occupied.) Then they found Asia, and the Arctic Ocean and the Bering Strait….

“It’s … Earth!”

The US president drew back his finger. The blue sphere in the sky was now growing at a rate visible without a reference object, and was now at least three times the diameter of the moon. At first, it looked like a balloon rapidly inflating in the sky, but then a shout from the crowd abruptly changed that impression:

“It’s falling!”

The shout provided a reasonable interpretation of the scene before them. Regardless of its accuracy, they immediately had a new sense of what was happening: another Earth was crashing toward them in space! The approaching blue planet now occupied a third of the sky, and surface details could be made out: brown continents covered in mountain wrinkles, cloud coverage looking like unmelted snow, outlined in black from the shadows cast on the ground. There was white at the North Pole, parts of which glittered—ice, rather than clouds. On a blue ocean, a snow-white object spiraled lazily with the delicate beauty of a velvet flower in a blue crystal vase—a newborn hurricane…. But when the huge blue sphere grew to cover half the sky, their perception experienced an almost simultaneous transformation.