Caldwell 63

Better known as the Helix Nebula, Hubble's image of Caldwell 63 is one of its most iconic.


650 light-years

Apparent Magnitude




object type

Planetary Nebula

This image shows a fine web of filamentary "bicycle-spoke" features embedded in the colorful red and blue ring of gas. At 650 light-years away, the Helix is one of the nearest planetary nebulae to Earth. A planetary nebula is the glowing gas around a dying, Sun-like star.
NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO)

Many of the Caldwell objects are millions of light-years distant, but Caldwell 63 is right in our cosmic neighborhood — only about 650 light-years away in the constellation Aquarius. Also cataloged as NGC 7293, Caldwell 63 is commonly called the Helix Nebula. It is a planetary nebula of gigantic proportions, with its bright ring stretching across nearly 3 light-years and dimmer, outer features extending even farther. Planetary nebulae like this one have no actual connection to planets but are called that because many of them have disk-like shapes that look like planets when viewed through small telescopes. They are produced as a medium-mass star dies and sloughs off its outer gaseous layers. These layers are expelled into space at astonishing speeds and glow from the energy given off by the dying star. The Helix Nebula is one of the closest planetary nebulae to Earth, giving scientists a detailed look at this type of stellar demise.

Comet-like tendrils cluster along the inner rim of the nebula’s reddish outer gas ring. This composite picture is a seamless blend of Hubble’s ultra-sharp images taken with the Advanced Camera for Surveys combined with the wide view of the Mosaic Camera on the National Science Foundation's 0.9-meter telescope at Kitt Peak National Observatory.
NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO)
Gases collide near the dying star that produced the Helix Nebula. Astronomers have dubbed the dark, tadpole-like objects in the upper right corner “cometary knots” because their glowing heads and gossamer tails resemble comets. Each gaseous head is at least twice the size of our solar system; each tail stretches 100 billion miles, about a thousand times Earth’s distance to the Sun.
C. Robert O'Dell and Kerry P. Handron (Rice University), NASA

Because it is so close, the Helix Nebula appears to be nearly half the width of the full moon. So to capture this view, Hubble astronomers had to take several exposures using the Advanced Camera for Surveys, which were then combined with the wide view of the Mosaic Camera on the National Science Foundation’s 0.9-meter telescope at Kitt Peak National Observatory. The colors in the image correspond to glowing oxygen (blue) and hydrogen and nitrogen (red).

Through Hubble’s observations of the nebula, scientists have made some startling discoveries. It seems that the Helix Nebula isn’t doughnut-shaped, as it appears. Instead it consists of two disks that are nearly perpendicular to each other — the inner part (the blue region in Hubble’s image) is “tipped” relative to the outer ring. Hubble has also imaged comet-like tendrils that form a pattern around the central star like the spokes on a wagon wheel. While these comet-like features were not a new discovery, Hubble has revealed that the gaseous knots likely result from a collision between gases. The dying star spews hot gas from its surface, which crashes into the cooler gas that it ejected 10,000 years before. Eventually the knots will dissipate into the cold blackness of interstellar space.

Discovered by German astronomer Karl Ludwig Harding in 1823, the Helix Nebula is a favorite target for amateur astronomers. It is best viewed in the early spring from the Southern Hemisphere, but can be found low in the autumn sky from the Northern Hemisphere. With a magnitude of 7.3, it can be seen with a small telescope or even binoculars under dark skies. A nebula filter will increase the contrast and offer even better views.

This star chart for Caldwell 63 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium


Comet - A relatively small, icy body orbiting the Sun (or another star), often producing a tail when approaching the Sun (or star).

Magnitude - The brightness of an astronomical object, represented by a number; bright objects have low numbers on the magnitude scale, while dim objects have high numbers.

Nebula - An interstellar cloud of dust and gas; either a location where new stars are being forged or a cloud of material ejected into space by a dying star.

Planetary Nebula - An expanding shell of gas around an aging or dying Sun-like star, cast off by the star.

Explore Hubble's Caldwell Catalog

The following pages contain some of Hubble’s best images of Caldwell objects.

Stars with four diffraction spikes dot the scene against a black backdrop.

Caldwell 1

Also known as NGC 188, this group of stars formed from a large cloud of gas making the stars roughly…

Red cloud of dust with a bright white star in the center of it. Lots of reddish and orangish stars in the background.

Caldwell 2

This shell of gas is expanding outward, away from the dying star within.

Large grouping of bright white, blue and red stars. Lightly colored blue dust surrounds the stars.

Caldwell 3

This barred spiral galaxy was first spotted by British astronomer William Herschel in April 1793 in the constellation Draco.