Sky & Telescope - February 2021 - 25

NGC 76 62: PE TER GOODHE W

THIN RING The extremely
faint Soap Bubble Nebula
(PN G75.5+1.7) lies close
to NGC 6888 at right. Both
objects ﬁt in the same ﬁeld
when targeted with modest
amateur equipment, but
long exposures and narrowband ﬁlters are required
to clearly resolve this ethereal planetary nebula.

smallest nebula included in my list. However, long exposures
show a larger, tenuous, complex outer shell that increases its
apparent size to nearly 6′. Imagers targeting NGC 6543 with a
pixel scale of less than 1 arcsecond can reveal its fascinating
symmetrical inner details. The Cat's Eye is circumpolar for
observers at mid-northern latitudes, though it's best seen in
summer when it transits high in the north.
Another frequently imaged planetary is NGC 7293, the
Helix Nebula. Residing in Aquarius, the Helix is the closest
planetary to Earth as well as the largest at 16′ × 12′, though
deep exposures show it covering an area almost the size of the
full Moon. Due to its proximity, the Helix presents a wealth
of detail in long exposures, including dense concentrations
appearing to radiate from the nebula's central star, and the
partial outer shell " eyebrow " along its northern edge. The
Helix appears primarily bluish, yellow, and red in naturalcolor photographs.
Our ﬁnal planetary is in Andromeda. Smaller than even
the Cat's Eye, NGC 7662 is often referred to as the Blue
Snowball Nebula. Burnham's Celestial Handbook describes it
as " vB, pS, R " - very bright, pretty small,
and round - which accurately sums up its
photographic appearance. Targeting this
planetary with modest equipment shows a
bright, round object with some structure
and a relatively uniform teal-colored disk.

few arcminutes or less in diameter. This can be both a blessing and a curse. Being small, they may cover only a few pixels
on your camera's sensor, limiting resolution. However, the ﬂip
side is that you don't require a large sensor. The best option
is to use a long-focal-length telescope and a high-sensitivity
detector. To get the most out of these targets, try to match
your imaging scale to about 1″ per pixel.
Because planetaries are emission nebulae, they are excellent targets for monochrome cameras equipped with narrowband ﬁlters. You can also achieve good results with oneshot-color (OSC) cameras and multi-band ﬁlters designed
speciﬁcally for using OSCs from light-polluted locales or
under moderate moonlight.
Some ﬁnd the natural colors of broadband images to be
more pleasing than narrowband palettes. Others, like myself,
prefer a mix of the two to retain natural star colors while also
recording faint nebulosity.
Roughly 3,000 planetary nebulae are known, and like
snowﬂakes, no two are quite the same. In fact, quite a few
(including the Soap Bubble) were recently discovered by
amateurs while imaging other targets, so be
sure to carefully check your images for tiny
greenish or blue spots that don't quite look
like stars.
Next time you're looking for a new challenge, consider targeting some of these glittering butterﬂies among the forest of stars.

Imaging Strategies
Most of these planetary nebulae are only a

RON BRECHER targets all types of deep-

X BLUE SNOWBALL Another small planetary with a
large, faint outer shell, NGC 7662 emits light almost
exclusively in the blue-green region of the spectrum.

sky objects from his backyard observatory in
Guelph, Ontario. See more of his deep-sky
astrophotography at astrodoc.ca.
sk yandtelescope.org * FEBRUARY 2 021

https://astrodoc.ca/ http://www.skyandtelescope.org

Sky & Telescope - February 2021

Table of Contents for the Digital Edition of Sky & Telescope - February 2021