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The Helix Nebula is one of the nearest planetary nebulae to Earth: a colorful ring of red and blue gas laced with fine, spoke-like filaments. A famous portrait of it blends sharp Hubble Space Telescope images with a wide view from the Mosaic Camera on the 0.9-meter telescope at Kitt Peak National Observatory, near Tucson, Arizona. Astronomers at the Space Telescope Science Institute stitched the Hubble frames into a mosaic, then merged it with the wider ground-based photo.
A tunnel, not a bubble
The Helix looks like a bubble, but careful analysis shows it's a cylinder — a trillion-mile-long tunnel of glowing gas that happens to point almost straight at Earth. Looking down it:
| Feature | What it is |
|---|---|
| Central star | a small, super-hot white dwarf |
| Thousands of comet-like filaments | lined along the inner rim, pointing back at the star; formed when a hot stellar wind slammed into colder shells of dust and gas the dying star had thrown off earlier. They may lie in a disk around the star, like a collar |
| Blue | glowing oxygen |
| Red | glowing hydrogen and nitrogen |
Ground-based telescopes had seen the filaments for decades, but never in such detail.
How big
| Distance | 650 light-years |
| Width | a ring nearly 3 light-years across — about three-quarters of the distance from the Sun to the nearest star |
| Size in the sky | nearly half the diameter of the full Moon |
Because it's so large on the sky, Hubble astronomers needed several exposures with the Advanced Camera for Surveys — nine separate snapshots in all — to capture most of it.
Photographed during a meteor storm
Hubble's time on the Helix came thanks to the Leonid meteor storm of November 2002. To protect the spacecraft and its precise mirror, controllers turned Hubble's back end into the meteor stream for about half a day. The Helix sat almost exactly in the opposite direction, so Hubble spent nine orbits photographing it while it waited out the storm.
What planetary nebulae are
Planetary nebulae have nothing to do with planets. They form late in the life of a Sun-like star, when a torrent of gas escapes the dying star. Through a small telescope they look like the disk of a planet, which is how they got the name; at higher magnification the classic "donut hole" in the middle shows.
See it yourself
The Helix is a favorite of amateur astronomers: through binoculars it's a ghostly, greenish cloud in the constellation Aquarius. Larger amateur telescopes show the ring, but only the largest ground-based telescopes can resolve its radial streaks.
Sources
Based on "Iridescent Glory of Nearby Helix Nebula" (PIA18164), National Aeronautics and Space Administration; a work of the United States government in the public domain. The composite image itself is not shown here: it blends Hubble data with a photograph from a National Science Foundation observatory.
Licens: CC0 1.0 (offentligt eje) · Bearbejdet efter images.nasa.gov
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