Avalon said, "That's assuming the Earth goes squarely in front of the Sun. When you see the eclipse before or after midpoint, at least part of the corona will stick beyond the Earth's sphere."

Peterborough said, "Part isn't the whole. It wouldn't be the same thing."

There was a short silence; and then Drake said, "I hope you don't mind if a fellow-chemist tries his hand at this, young man. I'm trying to picture the Earth in the sky, getting in the way of the Sun. And if we do that, then there's this to consider: the Earth has an atmosphere and the Moon has not.

"When the Moon moves in front of the Sun, as viewed from the Earth, the Moon's surface is sharp against the Sun. When the Earth moves in front of the Sun, as viewed from the Moon, the Earth's boundary is fuzzy and the Sun shines through Earth's atmosphere. Does that make a difference that you can use in the story?"

"Well," said Peterborough, "I've thought of that, actually. Even when the Sun is completely behind the Earth, its light is refracted through the Earth's atmosphere on every side, and a red-orange light penetrates it and reaches the Moon. It's as though the Moon can see a sunset all around the Earth. And that's not just theory. When there's a total eclipse of the Moon, you can usually see the Moon as a dull brick-red circle of light. It gleams in Earth's sunset atmosphere.

' 'As the eclipse, as viewed from the Moon, progresses, that side of the atmosphere that has just passed over the Sun is brighter, but grows gradually dimmer while the other side grows brighter. At eclipse mid-point, if you are viewing it from a part of the Moon which sees both Earth and Sun centered with respect to each other, the red-orange ring is evenly bright all the way around-assuming there isn't too much in the way of clouds in Earth's atmosphere at the time."

Drake said, "Well, for God's sake, isn't that a sufficiently spectacular sight for Victim to photograph? The Earth would be a black hole in the sky, with a thin orange rim all around. It would be-''