The Caldwell Objects

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outer shell falls upon the retina's rod-lined
of their characteristics suggest that FLIERs are
like sparks flung outward from the central star
about 1,000 years ago. Yet their shapes, as revealed
by HST, suggest that they are stationary,
and that material ejected from the star flows past
them, scraping gas from their surfaces.
It's best to approach this curious object in
four simple steps. First locate 3rd-magnitude
Delta (δ) Cygni, which marks the western arm of
the Northern Cross asterism. Seven degrees
north-northwest of Delta Cygni is 4th-magnitude
Iota (ι) Cygni. Next locate the beautiful
double star 16 Cygni 2¼° degrees to the southeast;
the sight of its 6th-magnitude Sun-like stars,
separated by 40", equals that of the planetary
itself. (What's more, we now know that the
southeastern member of the pair is orbited every
2.2 years by a planet or substellar brown dwarf
that may have as little as 1.5 times the mass of
Jupiter.) NGC 6826 is about ½° east-southeast of
periphery, which sends electrical signals to the the double. In fact, you can look for a "double
brain, making the outer shell suddenly pop into star" at the planetary's position, for it forms a
view. Alternating between direct and indirect pair with a much dimmer 12th-magnitude star
vision makes a double-shelled planetary appear 1.6' to the south. See if you can detect the
to blink.
planetary with 7x35 binoculars; the task should
The blinking phenomenon is a rather good be easy.
metaphor for the brief lives of these phantom gas At 23x through the 4-inch NGC 6826 is vir-
clouds. A planetary nebula lasts but for a "blink tually stellar, though averted vision and a few
of an eye" in astronomical terms. A Sunlike star minutes of staring shows its slightly swollen
can live for 10 billion years, but the shell we see form. Increasing the magnification to 72x reveals
around NGC 6826 will last for no more than the planetary as a small disk with a soft aqua hue
some 10,000 years. Hubble Space Telescope reminiscent of the colors one sees when peering
images of the Blinking Planetary cause us to at Uranus or Neptune through a telescope.
blink yet another way: in surprise. For in them Steven Hynes, the author of Planetary Nebulae,
we see mysterious knots of dense gas that noted a blue-green hue to NGC 6826 through his
astronomers have dubbed FLIERs (/ast l -o
w 10-inch reflector at 155x. At 189x in the 4-inch,
ionization emission regions). FLIERs cause the nebula's 10.6-magnitude central star stands
astronomers to blink because they challenge their out as a strong punctuation mark at the center of
understanding of planetary nebulae. No model of a large, diffuse shell of uniform light, though
stellar evolution presently can explain their there is a hint of brightening toward the central
existence. In one sense, says Bruce Balick star. Viewing through a 16½-inch telescope,
(University of Washington), some
Webb Society member
The Caldwell Objects 69