Why was I successful this time? For one thing, my eyes were better trained. A decade at the telescope made sure of that. The night was clear (absolutely no haze) and moonless, and my observing site was in a rural area far from any light pollution. It also provided an open southern horizon free of sky glow because the Helix is “way down there” at –21° declination. I used a low-power eyepiece (one that gave a 1° field of view in my scope to capture the Helix against a dark background) and didn’t even begin the search until I had allowed my eyes about 15 minutes to dark adapt. Try this strategy, and if all goes well, you’ll come face-to-face with the same phantom-like glow that greeted my eyes. With a medium- to large-aperture scope, you might even discern its annular form.
Last month, I commented on the fact that a majority of deep-sky objects show up telescopically as either starlike specks or faint fuzzies. The Helix Nebula is a “faint fuzzy” to the extreme — definitely not a visual “wow” object. We need to learn more about it to conjure up an intellectual “wow!”
We begin by traveling about 12,000 years back in time and some 650 light-years into space to a dying star. In its lifetime, it was similar in mass and size to our Sun. But with its hydrogen fuel depleted and its core collapsing, it has begun shedding its outer layers as an expanding envelope of gases.
Flash forward to the present, and these gases are still rushing outward at a speed of up to 16 miles (25 kilometers) every second. The tube-shaped envelope is now nearly 3 light-years across — more than two-thirds the distance between us and the star Alpha (α) Centauri. In its center, visible as a 13th-magnitude sun, is all that remains of the once vibrant star. About the size of Earth but with much of the mass of the original star, it’s a white dwarf so dense that a spoonful of its matter weighs several tons. Wow!
The Helix Nebula offers three visual challenges. Can you capture it through binoculars or a small telescope? What’s the smallest aperture with which you can discern its annular form? What’s the smallest aperture that allows you to spot its 13th-magnitude central star?
Questions, comments, or suggestions? Email me at
gchaple@hotmail.com. Next month: A star-hop in Aries. Clear skies!