Caldwell 63
NGC 7293, Helix Nebula
47’ x 31’ | 0.3”/px | 9436 × 6255 px | full resolution
Aquarius
RA 22h 29m 39s Dec -20° 50’ 25” | 0°
Caldwell 63, also known as NGC 7293 or the Helix Nebula, is a planetary nebula (PN) located in the constellation Aquarius. Discovered by Karl Ludwig Harding, most likely before 1824, this object is one of the closest of all the bright planetary nebulae to Earth. The distance, measured by the Gaia mission, is 655±13 light-years. Its age is estimated to be 10600 years. It is similar in appearance to the Cat's Eye Nebula and the Ring Nebula, whose size, age, and physical characteristics are in turn similar to the Dumbbell Nebula, differing only in their relative proximity and the appearance from the equatorial viewing angle. The Helix Nebula has sometimes been referred to as the "Eye of God" in pop culture, as well as the "Eye of Sauron". The Helix Nebula is an example of a planetary nebula, formed by an intermediate to low-mass star, which sheds its outer layers near the end of its evolution. Gases from the star in the surrounding space appear, from Earth's perspective, a helix structure. The remnant central stellar core, known as the central star (CS) of the planetary nebula, is destined to become a white dwarf star. The observed glow of the central star is so energetic that it causes the previously expelled gases to brightly fluoresce. The size of the inner disk is 8×19 arcmin in diameter. The outer torus is 12×22 arcmin in diameter and the outer-most ring is about 25 arcmin in diameter. The outer-most ring appears flattened on one side due to it colliding with the ambient interstellar medium. The Helix Nebula was the first planetary nebula discovered to contain cometary knots. 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. These knots are radially symmetrical (from the CS) and are described as "cometary", each centered on a core of neutral molecular gas and containing bright local photoionization fronts or cusps towards the central star and tails away from it. All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of the Solar System, while each of the cusp knots are optically thick due to Lyc photons from the CS. There are about 40,000 cometary knots in the Helix Nebula. The knots are probably the result of Rayleigh-Taylor instability. The low density, high expansion velocity ionized inner nebula is accelerating the denser, slowly expanding, largely neutral material which had been shed earlier when the star was on the Asymptotic Giant Branch. The central star of the Helix Nebula is a white dwarf of spectral type DAO. The star has a radius of 0.025 solar radii (17,000 km), a mass of 0.678 M☉, a temperature of 120,000 Kelvin and has an apparent magnitude of 13.5.
source: Wikipedia
Data Acquisition
Data was collected over 10 nights from September until November 2025, using a 14” reflector telescope with full-frame camera at the remote observatory in Spain. Narrowband filters (Ha, OIII and SII, all 3nm) were used to gather the data. A total of approximately 23 hours of data was combined to create the final image.
Location Remote hosting facility IC Astronomy in Oria, Spain (37°N 2°W)
Sessions
Frames
Equipment
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14 (2563mm @ f/7.2), Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro (full frame), cooled to -10 ºC
Chroma 2” Ha, OIII, SII (3nm) unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.9.3
Processing
All processing was done in Pixsinsight unless stated otherwise. Default features were enhanced using scripts and tools from RC-Astro, SetiAstro, GraXpert, CosmicPhotons and others. Images were calibrated using 50 Darks, 50 Flats, and 50 Flat-Darks, registered and integrated using WeightedBatchPreProcessing (WBPP). The processing workflow diagram below outlines the steps taken to create the final image.
The Helix Nebula can be imaged in RGB as well as in SHO colours. Each colour palette will have its own characteristics. With data collected here in the SHO palette, it was difficult to get the colours right in a pleasing manner, while maintaining the detail in the fainter outer areas of the nebula. Various different automatic stretching techniques were applied. But best results were obtained with careful manual stretching using multiple GHS runs for each of the individual colour channels separately. Also it was found to be beneficial for the final result to apply noise reduction and LocalHistogramEqualization to the individual colour channels. This way more of the structure remained visible in the final result.
The rest of the editing followed a pretty standard processing workflow.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
