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Donald Savage
Headquarters, Washington          May 9, 2003
(Phone: 202/358-1547)

Kathie Coil
Kitt Peak National Observatory, Tucson, Ariz.
(Phone: 520/318-8214)

Ray Villard
Space Telescope Science Institute, Baltimore
(Phone: 410/338-4514)

RELEASE: 03-162

IRIDESCENT GLORY OF NEARBY PLANETARY NEBULA SHOWCASED

In one of the largest and most detailed celestial
images ever made, the coil-shaped Helix Nebula is being 
unveiled today in celebration of Astronomy Day (Saturday, 
May 10). 

The composite picture is a seamless blend of ultra-sharp 
NASA Hubble Space Telescope (HST) images combined with the 
wide view of the Mosaic Camera on the National Science 
Foundation's 0.9-meter telescope at Kitt Peak National 
Observatory, part of the National Optical Astronomy 
Observatory, near Tucson, Ariz. Astronomers at the Space 
Telescope Science Institute (STScI) assembled the images 
into a mosaic. The mosaic was blended with a wider 
photograph taken by the Mosaic Camera. The image shows a 
fine web of filamentary "bicycle-spoke" features embedded in 
the colorful red and blue gas ring, which is one of the 
nearest planetary nebulae to Earth.

Because the nebula is nearby, it appears as nearly one-half 
the diameter of the full moon. This required HST astronomers 
to take several exposures with the Advanced Camera for 
Surveys to capture most of the Helix. HST views were blended 
with a wider photo taken by the Mosaic Camera. The portrait 
offers a dizzying look down what is actually a trillion-
mile-long tunnel of glowing gases. The fluorescing tube is 
pointed nearly directly at Earth, so it looks more like a 
bubble than a cylinder. A forest of thousands of comet-like 
filaments, embedded along the inner rim of the nebula, 
points back toward the central star, which is a small, 
super-hot white dwarf. 

The tentacles formed when a hot stellar "wind" of gas plowed 
into colder shells of dust and gas ejected previously by the 
doomed star. Ground-based telescopes have seen these comet-
like filaments for decades, but never before in so much 
detail. The filaments may actually lie in a disk encircling 
the hot star like a collar. The radiant tie-die colors 
correspond to glowing oxygen (blue) and hydrogen and 
nitrogen (red).

Valuable Hubble observing time became available during the 
November 2002 Leonid meteor storm. To protect the HST, 
including its precise mirror, controllers turned the aft end 
into the direction of the meteor stream for about half a 
day. Fortunately, the Helix Nebula was almost exactly in the 
opposite direction of the meteor stream, so Hubble used nine 
orbits to photograph the nebula, while it waited out the 
storm. To capture the sprawling nebula, Hubble had to take 
nine separate snapshots. 

Planetary nebulae, like the Helix, are sculpted late in a 
star's life by a torrential gush of gases escaping from the 
dying star. They have nothing to do with planet formation, 
but got their name because they look like planetary disks 
when viewed through a small telescope. With higher 
magnification, the classic "donut-hole" in the middle of a 
planetary nebula can be resolved. Based on the nebula's 
distance of 650 light-years, its angular size corresponds to 
a huge ring with a diameter of nearly three light-years. 
That's approximately three-quarters of the distance between 
our sun and the nearest star.

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. After 
careful analysis, astronomers concluded the Nebula really 
isn't a bubble, but is a cylinder that happens to be pointed 
toward Earth.

Information about the Helix Nebula and images are available 
on the Internet at:

http://hubblesite.org/newscenter/2003/11

The Space Telescope Science Institute (STScI) is operated by 
the Association of Universities for Research in Astronomy, 
Inc. (AURA), for NASA, under contract with the Goddard Space 
Flight Center, Greenbelt, Md. The Hubble Space Telescope is 
a project of international cooperation between NASA and the 
European Space Agency (ESA). Kitt Peak National Observatory, 
part of the National Optical Astronomy Observatory, is 
operated by AURA, under a cooperative agreement with the 
National Science Foundation.

For information about NASA, HST, or other Space Science 
projects on the Internet, visit:

http://www.nasa.gov

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