Tower of Glass Read Online Free PDF Page A

strewn spectacularly across the dome above him. He sought the near stars, those within the dozen-light-year radius that man’s stellar probes had reached in his own lifetime: Epsilon Indi, Ross 154, Lalande 21185, Barnard’s Star, Wolf 359, Procyon, 61 Cygni, He looked toward Taurus and found red Aldebaran glowing in the face of the Bull, with the Hyades clustered far behind, and the Pleiades burning in their brilliant shroud. Again and again the pattern on the dome shifted as focuses narrowed, as distances grew. Krug felt thunder in his breast. Vargas had said nothing since the planetarium had come to life.
    “Well?” Krug demanded at last. “What am I supposed to see?”
    “Look toward Aquarius,” said Vargas.
    Krug scanned the northern sky. He followed the familiar track across: Perseus, Cassiopeia, Andromeda, Pegasus, Aquarius. Yes, there was the old Water-Carrier, between the Fishes and the Goat. Krug struggled to recall the name of some major star in Aquarius, but came up with nothing.
    “So?” he asked.
    “Watch. We sharpen the image now.”
    Krug braced himself as the heavens rushed toward him. He could no longer make out the patterns of the constellations; the sky was tumbling, and all order was lost. When the motion ceased, he found himself confronted by a single segment of the galactic sphere, blown up to occupy the whole of the dome. Directly above him was the image of a fiery ring, dark at the core, rimmed by an irregular halo of luminous gas. A point of light glimmered at the nucleus of the ring.
    Vargas said, “This is the planetary nebula NGC 7293 in Aquarius.”
    “And?”
    ‘It is the source of our signals.”
    “How certain is this?”
    “Absolutely,” the astronomer said. “We have parallax observations, a whole series of optical and spectral triangulations, several confirming occultations, and much more. We suspected NGC 7293 as the source from the beginning, but the final data was processed only this morning. Now we are sure.”
    Dry-throated, Krug asked, “How distant?”
    “About 300 light-years.”
    “Not bad. Not bad. Beyond the reach of our probes, beyond the reach of efficient radio contact. But no problem for the tachyon-beam. My tower is justified.”
    “And there still is hope of communication with the senders of the signals,” Vargas said. “What we all feared—that the signals came from some place like Andromeda, that the messages had begun their journey toward us a million years ago or more—”
    “No chance of that now.”
    “No. No chance.”
    “Tell me about this place,” Krug said. “A planetary nebula—what kind of thing is that? How can a nebula be a planet?”
    “Neither a planet nor a nebula,” said Vargas, beginning to pace again. “An unusual body. An extraordinary body.” He tapped the case of Centaurine proteoids. The quasi-living creatures, irritated, began to flow and twine. Vargas said, “This ring that you see is a shell, a bubble of gas, surrounding an O-type star. The stars of this spectral class are blue giants, hot, unstable, remaining on the main sequence only a few million years. Late in their life-cycle some of them undergo a catastrophic upheaval comparable to a nova; they hurl forth the outer layers of their structure, forming a gaseous shell of great size. The diameter of the planetary nebula you see is about 1.3 light-years, and it is growing at a rate of perhaps fifteen kilometers a second. The unusual brightness of the shell, let me say, is the result of a fluorescence effect: the central star is producing great quantities of short-wavelength ultraviolet radiation, which is absorbed by the hydrogen of the shell, causing—”
    “Wait a minute,” Krug said. “You’re telling me that this stellar system has been through something like a nova, that the explosion took place so recently that the shell is only 1.3 light-years across even though it’s growing at fifteen kilometers a second, and that the central sun is tossing out