Washington DC
A CONSTELLATION of communications satellites has become the latest
astronomical nuisance. The satellites wink brightly in the night sky as they
reflect sunlight onto the Earth.
Since May, Iridium LLC, an international consortium based in Washington DC,
has been launching satellites into a 780-kilometre orbit. Forty-six of the 72
planned satellites鈥�66 operational and six spares鈥攁re now in place.
The satellites will provide a global mobile phone network.
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Unfortunately, the three antennas on each satellite form a pyramid facing the
ground, and they are highly reflective. 鈥淔or all intents and purposes, they鈥檙e
mirrors,鈥� says Rob Matson, an aerospace engineer with the consulting firm
Science Applications International Corporation in Los Angeles who also writes
software to track satellites. 鈥淚t鈥檚 not as bright as the full Moon, but it鈥檚
brighter than anything else,鈥� he says. 鈥淵ou can see it behind clouds.鈥�
Viewed from the ground, an Iridium satellite produces a flare lasting up to
20 seconds. At its peak intensity鈥攚hich can last for 5 seconds鈥攖he
flash is up to 23 times as bright as Venus. And for most of its orbit, each
satellite will be reflecting sunlight somewhere on Earth.
Radio astronomers have already fallen foul of terrestrial cellphone signals,
which are clogging up the radio spectrum
(鈥淎re we killing astronomy?鈥�, New 杏吧原创, 24 August 1996, p 28).
鈥淭hose cellphones are horrible,鈥� says Dan Green of the Harvard-Smithsonian
Center for Astrophysics in Cambridge, Massachusetts.
The Iridium satellites will add to radio astronomers headaches. But the
flashes will also annoy astronomers working at visible wavelengths. 鈥淔or
professional astronomers, they鈥檙e not a problem,鈥� says Green. 鈥淏ut an amateur
might be convinced that he鈥檚 seen a new nova. They get angry when you try to
tell them otherwise. It wastes a fair amount of our time and effort.鈥�