Helix Nebula With Radial Spokes

Helix Nebula With Radial Spokes

NGC 7293

Constellation: Aquarius
Ra: 22h 30m 15s
Dec: -20d 46m 48s
Distance: 700 light years
Image Size: 20' x 20'
North: Upper left



Selected as Astronomy Picture of the Day (APOD), September 4, 2008
Cover, Practical Astronomer, October, 2008 + Centerfold, pp 34-35

This image was composed with 3 nm H-a data mapped to red and 3 nm OIII data mapped to blue and green with RGB data blended in for star color. The increased contrast of the 3 nm H-a narrowband filter brought out the extended halos on both sides of the nebular structure in the color image. There appears to be two "loops" on the right side of the nebula.

This unusual image of the large Helix Nebula takes advantage of the detail provided by the Astrodon 3 nm OIII filter, which shows numerous radial projections, as shown below.

These radial spokes have surprised many, but they are clearly present in the famous Hubble Space Telescope color mosaic image of the Helix Nebula. The HST write-up states "The image shows a fine web of filamentary "bicycle-spoke" features embedded in the colorful red and blue gas ring……….". It further goes on to state with regard to visual observations "The Helix Nebula is a popular target of amateur astronomers and can be seen with binoculars as a ghostly, greenish cloud in the constellation Aquarius. Larger amateur telescopes can resolve the ring-shaped nebula, but only the largest ground-based telescopes can resolve the radial streaks." The above images show how modern CCD cameras and narrowband filters can bring out such fine details.

The image below came from the OIII filter (F502N) used to make their mosaic (h_helix_502_s2cc_img.fits) in the "Cosmetically Cleaned Mosaics Section. It clearly shows the radial spokes.

Exposure: 9.6 hrs Total: 4hrs H-a, 5 hrs OIII, 42 min RGB
Telescope: RCOS 16
Mount: Software Bisque Paramount ME
Oag: Astrodon MonsterMOAG
Acquisition: CCD AutoPilot4
Calibration: CCDStack2
Observatory Site: Sierra-Remote Observatories, Shaver Lake, CA
Camera: Apogee U16M
Filters: Astrodon 3nm OIII, H-a, Gen 2 RGB
Guider: SBIG ST-402
Camera Operation: MaximDL4.62
Processing: Photoshop CS3
Image Date: 08/27/2008

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