We have traveled the invisible universe of radio astronomy and taxed our imaginations as we struggled to comprehend the enormity of radio galaxies and quasars and the pervasive presence of black holes in space. We have visited clouds of molecules between the stars and seen the wonders at the center of the Galaxy. Now we should stop for a moment and ask how much longer will radio astronomy last?
This question is not asked lightly. Radio astronomers observe in the radio frequency part of the electromagnetic spectrum, but there are many people who would like to use those same radio bands for other purposes. Some of the more obvious groups (or services) with an interest are the communications and entertainment industries, the military, and NASA. Cell phones, wireless networks, GPS. and a host of other "new fangled" uses of the electromagnetic spectrum come at a price. They all need parts of the radio band and pose a potential threat to radio astronomy by generating unwanted radio interference.
A radio signal leaking from a communications satellite can destroy hours of astronomical observations. To the radio astronomer such a signal appeal's as a flash bulb might appear to an optical astronomer trying to take a photograph of a distant galaxy. The radio frequency spectrum is a natural resource that is increasingly being commandeered by those who wish to use radio frequencies for commercial and military uses. Radio astronomers feel this takeover very keenly and although they have a voice in the World Administrative Radio Conference, which decides on how to share the radio spectrum, their lobbying power is not backed up by the dollars available to commercial and military interests. On the positive side the hydrogen-line hand around 1,420 MHz is well protected, as are several other bands centered on the spectral lines of astronomically interesting molecules such as OH.
Basically the radio astronomers want to keep the radio spectrum as quiet as possible. All they want to do is listen to faint cosmic whispers. The irony is that while international agreement has created protected bands for the various services, such "protection from services in other bands shall be afforded the radio astronomy service only to the extent that such services arc protected from each other." Most other services do not care how much spurious radio energy is leaking from one radio band into another, because such leakage is usually well below their levels of interest. However, this leakage, due to poor design of transmitters, is a continual threat to radio astronomy. At issue is the fact that while a given service does make some effort to prevent excess leakage of unwanted signals into other bands, this concern is relative. Radio telescopes, capable of picking up faint signals from quasars 13 billion light-years away, are readily swamped by satellites leaking radiation in directions of little concern to their users.
The radio astronomy community has unusual needs, which those interested only in communications do not always see as a priority. The continuing threat is that the wonders of the invisible universe, now being so dramatically revealed, may be rendered invisible because of radio pollution generated by the technological nations on our planet.
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