Helix Nebula
astronomy
Also known as: NGC 7293
Learn about this topic in these articles:
planetary nebula
- In planetary nebula: Forms and structure
…the largest-known planetary nebulae, the Helix Nebula (NGC 7293) in the constellation Aquarius, subtends an angle of about 20 minutes of arc—two-thirds the angular size of the Moon. Planetary nebulae are considerably denser than most H II regions, typically containing 1,000–10,000 atoms per cubic cm within their dense regions, and…
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