"The two spacecraft are moving out of the huge glow of Lyman-alpha radiation in which the solar system is bathed and, being less blinded by it, perceive the much fainter radiation that comes from the galaxy," astronomer and lead researcher Rosine Lallement, with the Paris Observatory in Meudon, France, wrote in an email to Discovery News.
"It is like beginning to see small candles within a brightly lit room," she said.
The Voyager probes are crossing boundary regions in space where the amount of gas from the sun is subsiding and the amount of gas from the galaxy is increasing.
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The probes' power supplies are waning, which means many of the instruments, including a rotating platform for the spectrometer on Voyager 1, has had to be turned off, and which limits the amount of observing time, astronomer Jeffrey Linsky, with the University of Colorado in Boulder, told Discovery News.
The Voyager spacecraft generate electricity from heat emitted by the natural decay of radioactive plutonium, the same type of power system aboard Mars Science Laboratory, a NASA rover launched last week.