"Yes, but you cannot keep in this little Earthly shadow much longer; and what can we possibly do when we emerge into the fathomless, trackless effulgence of eternal sunshine? Let us turn back before we plunge into it," I pleaded.
"So that is what terrified you! Well, you have hit upon one of the greatest difficulties of the trip; but it is far from insurmountable. We will not turn back yet, especially as we have started in the most opportune time. You have mentioned this 'little shadow.' It is eight thousand miles wide at the surface of the Earth, and gradually, very gradually, tapers down to nothing far out in space. Have you ever calculated how far it reaches?"
"No," I answered. "But we moved out of it and back into it at the surface very easily, and besides, as the Earth moves forward in its orbit, the shadow will leave us."
"This little shadow is eight hundred and fifty-six thousand miles long, and we will never leave it as long as it lasts!" exclaimed the doctor. "Just at this time it points like a long arrow out in the direction of Mars. It is moving gradually as the Earth moves and hourly correcting its aim. At opposition time it will point directly and unerringly at Mars. Therefore it is a way prepared, surveyed, and marked for us through the all-enveloping sunlight, which otherwise would be dreadful enough."
"But how can we be sure of keeping in it? It is rapidly narrowing as it reaches farther out."
"I see I should have explained that to you before I went to sleep, and saved you this fright. The shadow now points behind Mars, as it is many days yet before it overtakes that planet in opposition. That is why I told you to steer always a little behind the planet. But you went a little out of the course, and immediately something warned us. That rim of light on the east of the Earth was notice to us that we were not in the centre of the shadow, but bearing too far to the left. We must keep absolutely in the dark of the Earth, with no light visible on either side of it. If a thin rim should appear on one side, we must turn toward the other until it is all dark again."
"Grant that this shadow is so enormously long, yet it is only scarcely one-fortieth of the distance to Mars," I objected. "After we emerge from it, what then?"
"With the aid of my telescope we shall probably be able to see the Earth as an orb, half or quarter as large as the Moon usually appears to us, and to observe its phases until we are several million miles from it. We must continue to keep the rim of light, which will then surround it, equal on all sides."
"Ah, but I am afraid," I interrupted, "that as soon as we pass out of this shadow the sunlight will be so bright that we cannot see any planets, not even the Earth. You know we cannot see the Moon only a quarter of a million miles away when the sun shines."
"In that case we must move the telescope to your window, put on a darkened lens, and steer so as to keep the Earth as a spot in the middle of the Sun. It must appear to us as Venus does to the Earth when she is making a transit across the face of the sun. But by our continual shifting we prevent the Earth from making a transit, and hold it as a steady spot in the centre of the Sun. This we can do for many, many million miles, continuing until we have reached the vicinity of Mars.