The Monogem Ring is a superbubble, discovered in the soft
X-ray energy band by ROSAT,
that lies about 1,000 light-years away in the constellations Monoceros
and Gemini. It is believed
to be the highly evolved remains of a supernova
that took place some 86,000 years. If it shone as brightly in visible light,
it would illuminate a region of the night sky about 25° across.
| ROSAT X-ray image of the Monogem