Sky & Telescope - February 2021 - 4

SPECTRUM

by Peter Tyson

Celestial Inkblot Tests

The Essential Guide to Astronomy
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COMMON NAMES FOR planetary nebulae are some of the most

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FEBRUARY 2 021 * SK Y & TELESCOPE

EDITORIAL
Editor in Chief Peter Tyson
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imaginative in astronomy. Partly that's because the ofﬁcial designations of these vestiges of dying stars range from the blandly
categorical (e.g., NGC 2346) to the truly ungainly (PN G75.5+1.7).
" Butterﬂy Nebula " and " Soap Bubble Nebula, " as the two objects
just mentioned are informally known, tickle our fancies a bit more.
Maybe it's in part because the term " planetary nebula " is a misnomer -
these gaseous blobs have nothing to do with planets - and when we shorten the
term to " planetaries " it's even more absurd. Likening distant clouds of gas and
dust to butterﬂies and soap bubbles jibes with that preposterousness.
But the main reason these entities offer such rich opportunities for whimsical christening is that they come in a dazzling array of evocative shapes, colors,
and nebulous textures. As our brains try to make sense of what we're seeing, we
naturally begin seeking resemblances to familiar things. Let the dubbing begin!
In his article on imaging planetary nebulae on page
18, Ron Brecher covers some of the better-known ones:
the Helix (NGC 7293), the Ring (M57), and the Cat's
Eye (NGC 6543), to name a few. But among the 3,000
or so planetaries that astronomers have so far identiﬁed in the Milky Way, we also have, among others, the
Lemon Slice Nebula (IC 3568), the Soccer Ball Nebula
(Kronberger 61), and the Glowing Eye Nebula (NGC
6751), also known as the Dandelion Puffball Nebula.
While all those are visible from the Northern HemiS The Dandelion Puffball
sphere, the Southern Hemisphere has its own potpourri
Nebula (aka NGC 6751)
of planetaries with clever eponyms. The Spirograph (IC
418), the Robin's Egg (NGC 1360), and the Engraved Hourglass (MyCn 18) all
visually call to mind their down-to-Earth counterparts. The southern planetary
OH 231.8+04.2 goes - thank goodness - by both the Calabash Nebula for its
shape and by the Rotten Egg Nebula for its known high sulfur content.
Some planetaries don't yet have established common names, which only take
hold when many astronomers start using them. In the meantime, one can have
fun coming up with one's own nicknames. I did just that after reading Brecher's
piece. You'll have to look these up, but I'd call NGC 5307 the Tardigrade Nebula,
NGC 2818 the Mantis-Eyed Nebula, and NGC 6326 the Kapow! Nebula.
To try your own hand at this celestial Rorschach test, open a web browser
and do an image search for " planetary nebula. " You'll hit upon both amateur
and professional images, many taken by the Hubble Space
Telescope. You can work your brain in a pleasurable way
dreaming up apt appellations for what you see. Who
knows? Maybe a common name of yours will stick.

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Sky & Telescope - February 2021

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