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."