“Let us take them out into the park under the trees,” my friend suggested.
The shafts of morning sunshine, falling through the branches and illuminating the broad lawns and brilliant flower-beds, offered the greatest possible contrast with the strange scenes of the preceding night. We chose the shadow of a huge elm, and had a table placed there for our accommodation. On this I spread the photographs, and my companion began to examine them with many expressions of interest.
“It is not often,” I said, “that science finds so flattering an audience.”
“And I hope, surely, never so small a one,” she responded, laughing. “But you must admit that science very seldom presents herself in so attractive a form as that of these pictures.”
“They are indeed of the highest excellence,” I replied. “It is the very moon herself that you see there.”
“But are you certain that they have not been embellished? Has not the hand of an artist retouched and improved them—particularly these large ones that seem to contain a thousand curious things which I can hardly believe really exist on the moon?”
“No,” I said, “there is nothing fictitious or imaginary in what you see. The only art displayed here is that of the astronomer-photographer, whose greatest ambition is to make his pictures absolutely true to nature. A defect in one of his plates, producing the appearance of a speck of light or shadow which does not actually exist, causes him as much distress of mind as you would experience upon hearing a false note from your piano. Indeed, the astronomer is so desirous of having nothing but the truth represented in his pictures that he often prefers, for his own study, the original negatives alone, because every time that they are reversed to make a ‘positive’ copy something is sure to be lost, and some slight defect is certain to be introduced. Let us begin, if you please, with the series of smaller pictures showing the various phases, and the gradual advance of daylight across the moon’s surface. Take first the photograph which I have labeled No. 1. It shows the New Moon when it is between three and four days old. You must often have seen it in that form in the western sky soon after sunset. Photographs of the New Moon have been made when the crescent is still narrower than that here shown, but there is no such photograph in this series, and it would possess little interest for you because almost no details of mountains, craters, and plains would be visible. It is hardly possible to make a good photograph of the moon when it is only one or two days from the sun in its monthly journey, on account both of the glare of the solar light in our atmosphere and of the nearness of the moon to the horizon, where the air lacks transparency and steadiness. In the photograph before us you will observe a great number of strange forms and shadings. I shall tell you what these are presently, but first let me call your attention to the fact that the picture does not exhibit a phenomenon which you would behold if you were actually looking at the moon in the phase here represented. You see here the New Moon very clearly, but not the Old Moon in her arms.”
“Indeed! It is a pity that the photograph does not show so interesting a sight.”
“Yes, it is a pity. The cause lies in the defect of light from what I have called the ‘Old Moon.’ The part that we see in the photograph is illuminated with sunshine, while the remainder of the moon reflects only the earthshine, which is too faint to be photographed (at least with the amount of exposure required to make a good picture of the brightly lighted crescent); although, as I have said, you would see it clearly if you were looking at the New Moon herself.”
