“I don’t see why you’re so surprised by this one plate, though.”

“Well, look at this dark circular patch. It’s obviously a dark cloud obscuring the light from the stars that lie beyond it. Such globules are not uncommon in the Milky Way, but usually they’re tiny things. My God, look at this! It’s huge, it must be the best part of two and a half degrees across!”

“But, Dr Marlowe, there are lots of clouds bigger than this, especially in the region of Sagittarius.”

“If you look carefully at what seem like very big clouds, you’ll find them to be built up of lots of much smaller clouds. This thing you’ve got here seems, on the other hand, to be just one single spherical cloud. What really surprises me is how I could have missed anything as big as this.”

Marlowe looked again at the markings on the plate.

“It is true that it’s in the south, and we’re not so concerned with the winter sky. Even so, I don’t see how I could have missed it when I was working on the Trapezium in Orion. That was only three or four years ago and I wouldn’t have forgotten anything like this.”

Marlowe’s failure to identify the cloud — for this is undoubtedly what it was — came as a surprise to Jensen. Marlowe knew the sky and all the strange objects to be found in it as well as he knew the streets and avenues of Pasadena.

Marlowe went over to the sideboard to renew the drinks. When he came back, Jensen said:

“It was this second plate that puzzled me.”

Marlowe had not looked at it for ten seconds before he was back to the first plate. His experienced eye needed no ‘blinker’ to see that in the first plate the cloud was surrounded by a ring of stars that were either absent or nearly absent in the second plate. He continued to gaze thoughtfully at the two plates.

“There was nothing unusual about the way you took these pictures?”

“Not so far as I know.”