September 19, 2008

In Today's One Minute Astronomer...

A Star's Life, Part 2

In July, we went through the basic idea of how a dying star flares into a planetary nebula. But enough science. Here are some spectacular planetary nebulae you can see from your backyard with a small telescope or pair of binoculars.

The Basics

• There are dozens of planetaries worth examining in an inexpensive 4" to 6" telescope. Perhaps the most famous planetary is M57, the Ring Nebula in Lyra. It looks like a ghostly smoke ring set against a dazzling backdrop of summer stars. Use your star map to find it on a line between beta and gamma Lyrae, a little closer to beta.

• Not far away, you'll find M27, the Dumbbell Nebula in the constellation Vulpecula. M27 is a whitish hourglass-shaped planetary. At magnitude 7.6, it's bright enough see with binoculars.

• Another summer favorite is the "Blinking Nebula", NGC 6826, in Cygnus. It appears to blink off and on as you alternate between direct and averted vision. The star you see at the center of the nebula is the dying star that's throwing off the nebula.

• The Helix Nebula (NGC 7293) in Aquarius is the closest planetary to Earth. But it's hard to see because it's spread out over a large area, making it appear visually dim.

M27, the "Dumbbell Nebula"

A Deeper Look

• These are just a few of the 1,500 planetary nebulae visible from Earth. Astronomers guess there must be 10,000 more obscured by the dusty plane of the Milky Way.

• To get the best view of planetaries and see detail in the disk, take the magnification up to at least 100x or so. And use a special OIII filter. It passes the blue-green light from the ionized oxygen in the nebulae and blocks the light pollution scattered in the surrounding sky. You'll see an amazing improvement in contrast when you use these filters. Well worth the investment.

Good To Know

You may wonder why, if nearly all mid-sized stars become planetary nebula for a time, and there are billions such stars in the galaxy, we see so few planetaries in the sky. The answer is that planetary nebula last for a very short time, maybe 50,000 years out of a 10 billion year stellar lifetime. So the chances of any star showing itself as a planetary nebula during our lifetime is very small.

Personal View

The best part of observing planetary nebulae- like most astronomical objects-lies not in what you see, but in what you imagine. When I look at a planetary nebula, I can't help but wonder what stories have played out in the center of the smoky green disk in my telescope's field of view. Were there intelligent beings on planets around the central star? How did they face the end of their world? Did they have an advanced civilization and enough technical skill to escape their fate?

And when our sun swells and scorches the surface of our fair planet, how will the inhabitants of the Earth-whoever or whatever they may be-face their certain destruction?

Things to think about in the dark of night as you peer through your eyepiece. Which is why astronomy, when you use your imagination, will never, ever get dull.

---------------- Highly Recommended ----------------

Join master science writer Timothy Ferris as he tours the known universe and reveals the technological revolution sweeping amateur astronomy. One of the most elegant and poetic books about stargazing ever written. Learn more...

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