GemingaArticle Free Pass Geminga, isolated pulsar (a rapidly
rotating neutron star) about 800 light-years from Earth in the
constellation Gemini, unique in that about 99 percent of its
radiation is in the gamma-ray region of the spectrum. Geminga is
also a weak X-ray emitter, but it was not identified in visible
light (as a 25th-magnitude object) until nearly two decades
after its discovery in 1972. It was the first pulsar not
detected at radio wavelengths. It pulsates with a period of
0.237 second, has a radius of about 10 km (6 miles), and
probably originated in a supernova explosion about 300,000 years
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