Avalon said, "Good! It helps, when one is going to talk about eclipses, if one knows something about them. Trying to write on a subject concerning which one is ignorant is a sure prescription for failure."

Gonzalo said, "Is the woman you're interested in an eclipse buff."

"No," said Peterborough. "I wish she were."

"You know," said Gonzalo, "if she doesn't share your interests, you might try finding someone who does."

Peterborough shook his head. "I don't think it works that way, Mr. Gonzalo."

"It sure doesn't," said Trumbull. "Shut up, Mario, and let him talk."

Peterborough said, "Murderer and Victim are both taking eclipse photographs; and, against all expectations, Victim, who is the underdog, the born loser, takes the better photograph; and Murderer, unable to endure this, decides to kill Victim. From there on, I have no trouble."

Rubin said, "Then you have your motive. What's your problem?''

"The trouble is-what kind of a better photograph? An eclipse photograph is an eclipse photograph. Some are better than others; but, assuming that both photographers are competent, not that much better. Not a murder's-worth better."

Rubin shrugged. "You can build the story in such a way as to make even a small difference murder-worthy-but I admit that would take an experienced hand. Drop the eclipse. Try something else."

"I can't. The whole business of the murder, the weapon and the detection depends on photography and eclipses. So it has to stay."

Drake said softly, "What makes it a science fiction story, young man?"

"I haven't explained that, have I?-I'm trying to tell as little as possible about the story. For what I'm doing, I need advanced computers and science fictional photographic gimmickry. One of the two characters-I'm not sure which- takes a photograph of the eclipse from a stratospheric jet."

"In that case, why not go whole hog?" said Gonzalo. "If it's going to go science-fictional… Look, let me tell you how I see it. Murderer and Victim are eclipse buffs and Murderer is the better man-so make it Murderer who's on that plane, and taking the best eclipse photograph ever seen, using some new photographic gimmick he's invented. Then have Victim, against all expectation, beat him out. Victim goes to the Moon and takes the eclipse photograph there. Murderer is furious at being beaten, goes blind with rage and there you are."

Rubin said energetically, "An eclipse photo on the Moon?"

"Why not?" said Gonzalo, offended. "We can get to the Moon right now so we can certainly do it in a science fiction story. And there's a vacuum on the Moon, right? There's no air. You don't have to be a scientist to know that. And you get a better picture without air. You get a sharper picture. Isn't that right, Milton?"

Peterborough said, "Yes, but-"

Rubin overrode him. "Mario," he said, "listen carefully. An eclipse of the Sun takes place when the Moon gets exactly between the Sun and the Earth. Observers on Earth then see the Sun blacked out because the opaque body of the Moon is squarely in front of it. We on Earth are in the Moon's shadow. Now if you're on the Moon," his voice grew harsh, "how the Hell can you be in the Moon's shadow?"

Avalon said, "Not so fast, Manny; an eclipse is an eclipse is an eclipse. There is such a thing as a Lunar eclipse, when the Earth gets between the Sun and the Moon. The Moon is in the Earth's shadow in that case and the whole Moon gets dark.

"The way I see it, then, is that Murderer takes a beautiful photograph of an eclipse on Earth, with the Moon moving in front of the Sun. He has advanced equipment that he has invented himself so that no one can possibly take a better photo of the moon in front of the Sun. Victim, however, goes him one better by taking an even more impressive photograph of an eclipse on the Moon, where, as Mario says, there is no air, with the Earth moving in front of the Sun."

Peterborough mumbled, "Not the same thing."

"It sure isn't," said Halsted, who had pushed his coffee cup to one side and was doing some quick figuring. "As seen from Earth, the Moon and the Sun have the same apparent width, almost exactly. Pure coincidence, of course; no astronomical necessity at all. In fact, eons past, the Moon was closer and appeared larger, and eons future, the Moon will be-Well, never mind. The fact is that the Earth is larger than the Moon, and from the Moon you see the Earth at the same distance that you see the Moon when you're standing on Earth. The Earth in the Moon's sky is therefore as much larger than the Moon in appearance as it is in actuality. Do you get that?"

"No," said Gonzalo, flatly.

Halsted looked annoyed. "Well, then, don't get it. Take my word for it. The Earth in the Moon's sky is about 3% as wide in appearance as the Moon is in Earth's sky. That means the Earth in the Moon's sky is also that much bigger than the Sun, because the Sun looks just the same from the Moon as from the Earth."

"So what's the difference?" said Gonzalo. "If the Earth is bigger, it gets in the way of the Sun that much better."

"No," said Halsted. "The whole point about the eclipse is that the Moon just fits over the Sun. It hides the bright circle of the gleaming Sun and allows its corona-that is, its upper atmosphere-to shine all about the hidden Sun. The corona gleams out in every direction with the light of the full Moon and does so in beautifully delicate curves and streamers.

"On the other hand, if you get a large body like the Earth in front of the Sun, it covers up the shining sphere and the corona as well. You don't see anything."

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-''

"No, sir," said Peterborough. "It isn't the same thing. It's too dull. It would be just a red-orange ring. Once the photograph is taken the first time, that would be it. It wouldn't be like the infinitely varying corona."