‘Clown Face Nebula’ is no laughing matter


By Tom Burns - Stargazing



Yes, it’s winter. When no moon brightens the sky, the dark surrounds you like a tattered blanket.

The only sound is the wind whistling past your ears and the faint squeak of telescopes slowly moving.

And it’s cold. The stiff breeze feels like a dull razor scraping against your skin. The metal of your telescope numbs your fingers.

As you stare through the eyepiece, you can feel the frozen glass sucking the heat from your eye.

“No wonder they call it the ‘dead of night,’” you whisper. You shouldn’t have spoken. Your breath has left a thick coat of frost on the eyepiece lens.

“There has got to be a better hobby,” you think, “preferably one that involves a roaring fire and a glass of hot cider.”

You need to cheer up — and fast. So you take a look at an object that is guaranteed to bring a smile to your chapped lips.

It’s the “Clown Face Nebula,” the shining remnant of a dying star.

To find it, first find the constellation Gemini, riding almost overhead around 9 p.m. Look for two bright stars called Castor and Pollux, sometimes called the “heavenly twins” because they are about equal brightness.

Starting from Pollux, the left-hand star, sweep down and to the right to Delta, marked with a “d” on most star maps. It is about midway down the constellation. The Clown Face, marked as NGC 2392, is about half a binocular field down and to the right from Delta.

You are looking at a “planetary nebula,” so-called because some 19th-century astronomers believed they were distant planets in our solar system. It’s easy to see why.

In a small telescope, the Clown Face Nebula looks like a tiny disk about the size of Jupiter. Because it glows a brilliant blue-green, it seems like a fuzzy simulacrum of the distant planets Uranus and Neptune.

Like a cosmic bullseye, an ancient star sits in the center of the blueish dot. Surrounding the star is a globe of gas called a nebula.

The Clown Face Nebula is much farther away than the planets. At about 6,500 light-years away, it is around 1.4 million times the distance to Neptune, the most distant planet.

In a small telescope, it is one of the best examples of an effect called “averted vision.”

The screen on the back of your eye, your retina, is more sensitive at the edges than the center. If you stare right at the central star, you can’t see the faint light of the nebulosity. Only the bright star remains.

If you look to the side of the object, the sensitive portion of the retina reveals the faint light of the nebulosity, and the star disappears, lost in the wash of nebulous light.

The central star of the Clown Face Nebula is an old dwarf that has imploded and thus reached the end of its life.

A more massive star might have exploded from the pressure. A star less massive star might continue percolating for hundreds of billions of years before it expired without much fuss.

As the Clown Face Nebula’s star began to die, it first swelled to enormous size as its hydrogen-fuel supply became depleted. At that “red-giant” phase, the star’s center is so pressurized and overheated that it blows the star’s outer shell away from the star.

As a result, the star sent part of its substance into space at a tremendous velocity — 250,000 miles per hour. All of that happened about 1,700 years ago.

It then collapsed to a white dwarf just a few thousand miles in diameter and got hotter still.

Its hydrogen bomb days may be over, but it now burns with white-hot intensity.

At over 53,000 degrees Fahrenheit on its surface, it burns almost six times hotter than our sun’s surface. The high temperature results from smashing down a giant star to a relatively tiny size.

Despite a white dwarf’s extraordinary heat and density, it is inherently stable. The Clown Face Nebula’s central star will radiate energy for hundreds of billions of years before it fades to black.

Meanwhile, the nebula continues to grow, not only because of its initial motion but also because of the pressure exerted upon it by the central star’s intense radiation.

Consequently, its substance gets spread out very thinly. About 1,700 years after the star’s collapse into a white dwarf, its surrounding nebula is now about four trillion miles in diameter.

If we could magically transport it to our solar neighborhood, the nebula would nearly fill the void between the sun and Proxima Centauri, the nearest star to the sun.

The nebula that glows so brightly in a telescope is, in fact, almost a perfect vacuum.

That we can see it at all is a tribute to the dying star. Radiation from the white dwarf causes its gassy shell to fluoresce like a spark of electricity causes the gas in a fluorescent bulb to glow.

Eventually, the nebula will disappear, its tenuous substance lost in the vast emptiness of space.

In these pandemic times, it’s tough to get excited about a glowing, blue ball so distant from our daily preoccupations on Earth.

Some of us turn to our pasts and remember better times.

I choose to imagine a distant future in which I will never participate.

In its youth and middle age, the Clown Face Nebula’s star was not so different than our sun. When we look at it, we see the future of our solar system in five or six billion years.

It is as if the star recognizes its end and tries bravely to create a tribute to itself. As L.H. Aller wrote, planetary nebulae are “wreaths placed by Nature around dying stars.”

The Clown Face Nebula has captured the imagination of amateur telescopists since its discovery by William Herschel in 1787.

In Robert Burnham’s Celestial Handbook, he writes that the nebula resembles comedian W.C. Fields.

Most observers think the Clown Face Nebula looks more like its other nickname, the “Eskimo,” which makes it particularly appropriate for cold-weather observing. In a large amateur telescope, the central star glows like a nose at the center of the nebulosity.

In a long-exposure image, the gas immediately surrounding the star takes on a shape that looks vaguely like a face. The ring of blueish gas and dust at the edge of the nebula makes the face look like it is enveloped in a furry parka, the ghostly headgear of a dying star.

However, on Aug. 5, 2020, NASA decided to nix the “Eskimo” designation because it is racially offensive to the Inuit people and other indigenous residents of northern climes.

In a statement on the subject, they declared that “’Eskimo’ is widely viewed as a colonial term with a racist history, imposed on the indigenous people of Arctic regions.”

NASA suggests that we refer to the nebula by its official designation — NGC 2392. But that seems a poor reflection of the object’s beauty.

NASA also rejected “Clown Face,” although I cannot see why clowns would be offended by their association with such a splendid astronomical object. Clowning is a noble and heartwarming profession that needs a bit of a boost after unjustifiably negative treatment in movies like “It.”

Others have suggested the name Lion Nebula, and the nebula does indeed resemble the head and mane of a lion.

However, the name is already taken by Sharpless 132, a glowing star-birthing region in the constellation Cepheus.

So, “Clown Face” it is.

No matter what you call it, the planetary nebula retains its radiant blue beauty.

Soon, I fervently hope, public observing programs will begin again in earnest, and amateur astronomers will again point their telescopes at the lion, clown face, or whatever you choose to call it.

I hope you, too, will someday be haunted by its shimmering, sapphire splendor.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.