Caldwell 55

Also known as the Saturn Nebula and NGC 7009, Caldwell 55 holds a dying star at its heart.


1,400 light-years

Apparent Magnitude




object type

Planetary Nebula

NGC 7009 has a bright central star at the center of a dark cavity bounded by a football-shaped rim of dense, blue and red gas. The cavity and its rim are trapped inside smoothly-distributed greenish material in the shape of a barrel and comprised of the star's former outer layers. At larger distances, and lying along the long axis of the nebula, a pair of red "ansae", or "handles" appears. Each ansa is joined to the tips of the cavity by a long greenish jet of material. The handles are clouds of low-density gas.
Bruce Balick (University of Washington), Jason Alexander (University of Washington), Arsen Hajian (U.S. Naval Observatory), Yervant Terzian (Cornell University), Mario Perinotto (University of Florence, Italy), Patrizio Patriarchi (Arcetri Observatory, Italy), NASA/ESA

Garden-variety stars like the Sun live fairly placid lives in their galactic neighborhoods, steadily churning out heat and light for billions of years. When these stars reach retirement age, however, they transform into unique and often psychedelic works of art. This Hubble image of Caldwell 55, also known as the Saturn Nebula and NGC 7009, shows the result, called a planetary nebula. While it looks like a piece of wrapped cosmic candy, what we see is actually the outer gaseous layers of a dying star.

Stars are powered by nuclear fusion, but each one comes with a limited supply of fuel. When a medium-mass star exhausts its nuclear fuel, it will swell up and shrug off its outer layers until only a small, hot core remains. The leftover core, called a white dwarf, is a lot like a hot coal that glows after a barbecue — eventually it will fade out. Until then, the cast-off gaseous debris fluoresces as it expands out into the cosmos, possibly destined to be recycled into later generations of stars and planets.

The Saturn Nebula is only about 1,400 light-years away in the direction of the Aquarius constellation. Its proximity has made it a popular target for study by telescopes all around the world. Hubble took this image in visible light using the Wide Field and Planetary Camera 2 in 1996. Using Hubble’s observations, scientists have characterized the nebula's composition, structure, temperature, and the way it interacts with surrounding material. Studying planetary nebulae is particularly interesting since our Sun will experience a similar fate around five billion years down the road.

The Saturn Nebula has been known since 1782 when it was discovered by astronomer William Herschel. Late summer skies will provide ideal viewing of this kaleidoscopic structure for Northern Hemisphere observers (late winter for those in the Southern Hemisphere). This magnitude-8 nebula will look like a star in smaller telescopes, but larger telescopes will reveal more detail, including two extended lobes on either side of the nebula that resemble the rings of Saturn, lending the nebula its nickname. Using high magnification along with averted vision (looking away from the center of the object) will provide the best views of the fainter exterior regions of the nebula.

For more information about Hubble’s observations of Caldwell 55, see:
Planetary Nebula NGC 7009

This star chart for Caldwell 55 represents the view from mid-northern latitudes for the given month and time.
Image courtesy of Stellarium


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.

White Dwarf - The core of a dead Sun-like star whose outer layers have been expelled into space.

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.