Helix Nebula
J2000 epoch | |
---|---|
Right ascension | 22h 29m 38.55s[1] |
Declination | −20° 50′ 13.6″[1] |
Distance | 200±1 pc (650±3) ly |
Apparent magnitude (V) | +7.6[1] |
Apparent dimensions (V) | 25′[2] |
Constellation | Aquarius |
Physical characteristics | |
Radius | 2.87 ly (0.88 pc)[2] ly |
Notable features | One of the nearest PNe |
Designations | NGC 7293[1] Caldwell 63 |
The Helix Nebula (also known as NGC 7293 or Caldwell 63) is a
General information
The Helix Nebula is an example of a
The nebula is in the constellation of Aquarius, and lies about 650 light-years away, spanning about 0.8 parsecs (2.5 light-years). Its age is estimated to be 10600+2300
−1200 years, based on the ratio of its size to its measured expansion rate of 31 km·s−1.[5]
Structure
The Helix Nebula is thought to be shaped like a
Expansion of the whole planetary nebula structure is estimated to have occurred in the last 6,560 years, and 12,100 years for the inner disk.[2] Spectroscopically, the outer ring's expansion rate is 40 km/s, and about 32 km/s for the inner disk.
Knots
The Helix Nebula was the first planetary nebula discovered to contain cometary knots.[12] Its main ring contains knots of nebulosity, which have now been detected in several nearby planetary nebulae, especially those with a molecular envelope like the Ring nebula and the Dumbbell Nebula.[13]
These knots are radially symmetric (from the CS) and are described as "cometary", each centered on a core of neutral molecular gas and containing bright local
The knots are probably the result of
The excitation temperature varies across the Helix nebula.[18] The rotational-vibrational temperature ranges from 1800 K in a cometary knot located in the inner region of the nebula are about 2.5'(arcmin) from the CS, and is calculated at about 900 K in the outer region at the distance of 5.6'.[18]
Videos
See also
- New General Catalogue (NGC)
References
- ^ a b c d "NGC 7293". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-07.
- ^ S2CID 119507454.
- S2CID 15427995.
- ^ "SIMBAD references".
- ^ doi:10.1086/340726.
- ^ "Urban Legends Reference Pages". The Eye of God. 5 February 2004. Retrieved 2007-07-16.
- ^ "The Eye of Sauron (aka NGC7293)". Sky and Telescope.
- ^ Nancy Atkinson (4 October 2012). "Eye-Like Helix Nebula Turns Blue in New Image". Universe Today. Archived from the original on 14 July 2014.
- doi:10.1086/307639.
- S2CID 15244406.
- ISSN 0004-637X.
- ^ "APOD: 2008 April 13 - Curious Cometary Knots in the Helix Nebula". apod.nasa.gov. Archived from the original on 2012-05-05.
- doi:10.1086/340726.
- doi:10.1086/186666.
- Bibcode:2003RMxAC..15...29O.
- S2CID 119252556.
- S2CID 120347309. Retrieved 22 November 2020.
- ^ S2CID 118514953.
External links
- NASA Astronomy Picture of the Day: The Helix Nebula (NGC 7293) (31 December 2009)
- NASA Astronomy Picture of the Day: The Helix Nebula (NGC 7293) (10 May 2003)
- NASA/JPL-Caltech - The Helix Nebula (NGC 7293)
- SEDS - The Helix Nebula (NGC 7293)
- NightSkyInfo – The Helix Nebula (NGC 7293)
- Snopes - Helix Eye of God - Urban Legend
- The Helix Nebula on
- Helix Nebula (NGC 7293) at Constellation Guide