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A dying star is throwing a cosmic tantrum in this combined image from NASA's Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX), which NASA has lent to the California Institute of Technology in Pasadena. In death, the star's dusty outer layers are unraveling into space, glowing from the intense ultraviolet radiation.

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The showpiece of the constellation Aquarius is the grand and elusive Helix Nebula, NGC 7293. One of the closest and apparently largest of all planetary nebulae, the Helix is one of the few sights that's easier to see in a small telescope than in a large one. In images, like the excellent collaboration above led by Warren Keller at BillionsandBillions.com, the nebula looks like an expansive eye in deep sky. Some refer to the Helix as the "Eye of God".

Like all planetary nebulae, the Helix is a region of rarefied gas thrown off by a dying star of moderate mass. The star is essentially ejecting its outer atmosphere and exposing its blazing hot core to full view. The Helix is distinguished by its proximity to Earth, about 700 light years, and its consequent very large apparent size. By comparison, the Ring Nebula in Lyra is some 2,000 light years away. The Helix gets its name from its ring-like appearance which resembles the two coils of a spring seen on axis.

When you first see the Helix Nebula, you may be astonished to discover how large it appears. Most planetaries are so small as to appear star-like, even at moderate power, so happening upon a planetary nebula that's half the size of the full Moon can be a little unsettling, even for experienced observers. The apparent surface area of the nebula is about four times larger than M27, the Dumbbell Nebula, and more than 100x the area of the Ring Nebula (M57)! Charles Messier missed this nebula, likely because his telescopes had a narrow field of view and did not enable him to notice a large object with low surface brightness.

The Helix Nebula is located about 10º NW of the bright star Fomalhaut. It looks like a big Moon-sized grey circle in a pair of binoculars. At low-to-medium power in a telescope, the nebula appears as a smokey oval set in a triangle of 10th-magnitude stars. At first it appears well defined and somewhat featureless. But keep looking. With averted vision, you'll begin to see the ring-like structure of this ghostly object in a 3″ to 4″ scope. The central region appears transparent at low power, and slightly brighter than the background sky at medium power. The 13th-magnitude central star is a challenge with a 4″ scope but a snap with a 6″ or 8″ reflector, especially at 80x. Notice how the bright outer ring appears better defined at its inner edge. A UHC or OIII filter is usually a big help with this nebula.

Some observers at high altitudes and under dry sky claim to have seen the Helix without optics. If you have exceptionally clear and dry skies, give it a try. This will be much easier at southern latitudes where the nebula can be observed much higher in the sky.

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The showpiece of the constellation Aquarius is the grand and elusive Helix Nebula, NGC 7293. One of the closest and apparently largest of all planetary nebulae, the Helix is one of the few sights that's easier to see in a small telescope than in a large one.

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The Helix nebula is not only one of the brightest near-Earth planetary nebula in the night sky, but it is also one of the most famous. The Helix nebula's unique appearance has earned it the pop culture nickname of "The Eye of God" and "The Eye of Sauron." Even NASA describes the Helix nebula like "a dying star that is throwing a temper tantrum."

Clearly, the Helix nebula brings up strong reactions in everyone who sees it! And at a brightness magnitude of 7.6, it is a popular choice for amateur astronomers because it is relatively easy to spot without advanced knowledge or training.

The classification of the Helix nebula as a "planetary nebula" is one that was coined in the 18th century by an astronomer named William Herschel, long ago before telescopes were of sufficient strength to help astronomers distinguish between planets and nebula. So originally, astronomers thought the Helix nebula and others like it were planets!

At its center is a dying star called a white dwarf star. Today, the white dwarf star that sits in the very center of the Helix nebula is about the size of the Earth but the entire structure has a mass much greater than Earth.

Surrounding the remains of the star itself are bands of gaseous matter. This is why photographs of the Helix nebula often make it look so colorful and so different from frame to frame. Different lens filters, from infrared to ultraviolet and others, can be applied to study different gaseous bands and properties.

Helix Nebula Profile

This data gives a basic overview of the composition of the Helix nebula.

Designation: Helix Nebula or NGC (New General Catalog) 7293
Type: Planetary nebula
Diameter: 2.87 light years
Distance: 655 light years
Mass: 0.93 M
Constellation: Aquarius

Facts About the Helix Nebula

The Helix Nebula is estimated to be about 10,600 years old.

Before the explosion that created the Helix Nebula, it is highly likely that a system of planets, natural interstellar moons, comets and other celestial objects orbited around the star in a way quite similar to how Earth and the other planets orbit around the Sun.

One of the most interesting aspects of the Helix Nebula for astronomers is that inside its gaseous bands are surviving comets. This very rarely happens once a dying star explodes.

When observed through binoculars or a telescope, the nebula itself is often likened to the size of one-half a full Moon. The glow that surrounds the Helix Nebula is caused by the ionizing impact of radiation being emitted by the dying star.

In about 5 billion years from now, the Sun will also go through its red giant phase, explode, and from that explosion enter its planetary nebula phase, burning off the surrounding gaseous bands as fuel until it dies out completely.

The Helix Nebula was originally discovered by a German astronomer named Karl Ludwig Harding. He discovered many other celestial objects in addition to the Helix Nebula. It is now thought that Harding made his discovery of the Helix Nebula before 1824, but the precise date is not known.

The Helix Nebula formed when a massive red giant star exploded, resulting in the white dwarf star at the nebula center that is now surrounded by continuously expanding bands of gases and dust.

While the Helix Nebula definitely appears to be a circular shape when viewed through a telescope, astronomers now believe it is actually more elongated. The reason Earth viewers don't see the elongation is because of the way the Helix Nebula faces Earth. If viewed from the side (away from Earth) the extended shape would become visible.

The Helix Nebula is so vast that Hubble telescope cameras had to take several separate photos to capture its full extent. The Hubble's operators then had to assemble the different photos together to get a more complete picture of the Helix Nebula. They then combined that photo together with another wide-angle photo taken at the Kitt Observatory and only then could they see the entire mass of the Helix Nebula.

Right now, the Helix Nebula is still incredibly hot and very active as the gaseous bands are used for fuel and burned away one by one. As this process continues, the entire structure will eventually cool.

The outermost gaseous bands are composed mostly of lighter gases like hydrogen and helium. Nearer the center are the heavier gases like oxygen, nitrogen and carbon. All of these gases are fuel sources that will eventually be exhausted one after another. When this happens, the star will die out completely.

Long filaments of hydrogen called "knots" extend outward from the center of the Helix nebula like spokes on a bicycle wheel. Each one of these knots on its own is the size of the entire solar system that surrounds Earth, and it is estimated there are around 20,000 such knots inside the Helix Nebula. However, astronomers are still trying to figure out what caused the knots to form. And in fact, the Helix Nebula is the first planetary nebula in which knots were discovered.

The entire Helix nebula is constantly being buffeted by strong solar winds that push at the gaseous bands and cause the nebula structure to expand. Right now, the Helix Nebula's innermost gaseous bands are expanding at an estimated rate of 31 km per second. The outermost gaseous bands are expanding at an estimated rate of 40 km per second.

On dark nights, it is often possible to observe the Helix nebula with a pair of good binoculars. However, a telescope is needed to view the gaseous bands that surround the central white dwarf star.

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Helix nebula - Facts and Info * The Planets

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Clearly, the Helix nebula brings up strong reactions in everyone who sees it! And at a brightness magnitude of 7.6, it is a popular choice for amateur astronomers because it is relatively easy to spot without advanced knowledge or training. The classification of the Helix nebula as a "planetary nebula" is one that was coined ...