Dis­tance Mark­ers

Air & Space Smithsonian - - Chatter -

ASTRONOMERS NEED some help from the uni­verse when mea­sur­ing vast dis­tances. These “light echoes” (be­low) em­anate from an X-ray blast pro­duced by the dou­ble star sys­tem Circi­nus X-1 in 2013. The light is re­flect­ing off nearby dust, which has en­abled astronomers to use NASA’S Chan­dra X-ray Ob­ser­va­tory to tri­an­gu­late the dou­ble star’s lo­ca­tion. Astronomers now know it is 30,700 light-years away, twice as far as pre­vi­ously thought.

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