ROBERT GENDLER / SCIENCE PHOTO LIBRARY ROBERT GENDLER / SCIENCE PHOTO LIBRARY
Star clusters M35 and NGC 2158, optical image. M35 is the diffuse group of blue stars left and slightly above centre, while NGC 2158 is the dense group at lower right. The clusters are unrelated, and occupy the same line of sight by chance. M35 is around 2800 light years away with NGC 2158 some 8400 light years beyond it. The stars in M35 are far younger, at around 150 million years old, and hence appear bluer. The blue stars in NGC 2158 have long since burnt out, and it appears yellower as the majority of the stars in it are long-lived yellow stars. Both clusters lie in the constellation Gemini.
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