And Michel, getting up, went to look at the lunar disc, which was shining with intolerable brilliancy.
"Faith!" said he, "it must be hot up there."
"Without reckoning," answered Nicholl, "that daylight lasts 360 hours."
"And by way of compensation night has the same duration," said Barbicane, "and as heat is restored by radiation, their temperature must be that of planetary space."
"Never mind! I should like to be there already! It will be comical to have the earth for a moon, to see it rise on the horizon, to recognise the configuration of its continents, to say to oneself, 'There's America and there's Europe;' then to follow it till it is lost in the rays of the sun! By-the-bye, Barbicane, have the Selenites any eclipses?"
"Yes, eclipses of the sun," answered Barbicane, "when the centres of the three stars are on the same line with the earth in the middle. But they are merely annular eclipses, during which the earth, thrown like a screen across the solar disc, allows the greater part to be seen."
"Why is there no total eclipse?" asked Nicholl. "Is it because the cone of shade thrown by the earth does not extend beyond the moon?"
"Yes, if you do not take into account the refraction produced by the terrestrial atmosphere, not if you do take that refraction into account. Thus, let _delta_ be the horizontal parallax and _p_ the apparent semidiameter--"
"Ouf!" said Michel, "half of _v_ zero square! Do speak the vulgar tongue, man of algebra!"
"Well, then, in popular language," answered Barbicane, "the mean distance between the moon and the earth being sixty terrestrial radii, the length of the cone of shadow, by dint of refraction, is reduced to less than forty-two radii. It follows, therefore, that during the eclipses the moon is beyond the cone of pure shade, and the sun sends it not only rays from its edges, but also rays from its centre."
"Then," said Michel in a grumbling tone, "why is there any eclipse when there ought to be none?"
"Solely because the solar rays are weakened by the refraction, and the atmosphere which they traverse extinguishes the greater part of them."
"That reason satisfies me," answered Michel; "besides, we shall see for ourselves when we get there. Now, Barbicane, do you believe that the moon is an ancient comet?"