description HB 21 Overview
HB 21 is a large supernova remnant in the constellation Cygnus, first identified as a radio source in 1953. It is classified as a mixed-morphology remnant, with a shell-like appearance at radio wavelengths and centrally concentrated thermal X-ray emission. Observations indicate interaction between the expanding remnant and nearby molecular clouds, making HB 21 useful for studying how supernova shocks affect dense interstellar gas and produce high-energy radiation.
help HB 21 FAQ
How good is HB 21?
HB 21 scores 6.86/10 (Fair) on Lunoo, making it rated in the Nebula category.
What are the best alternatives to HB 21?
See our alternatives page for HB 21 for a ranked list with scores. Top alternatives include: CTB 1, G1.9+0.3, Monoceros Loop.
How does HB 21 compare to CTB 1?
See our detailed comparison of HB 21 vs CTB 1 with scores, features, and an AI-powered verdict.
Is HB 21 worth it in 2026?
With a score of 6.86/10, HB 21 is a solid option in Nebula. See all Nebula ranked.
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