Sky and Telescope - February 2017 - 61

Famous Disappearing Act

Gemini Spawns Geminids
◗ Gemini hosts one of the best annual meteor showers,
albeit at a wintry time of the year - the night of December 12-13. The prospects for the 2017 Geminid shower
are almost ideal, as there will be virtually no interference
from moonlight. If you can travel away from city lights,
you might spot several dozen "shooting stars" per hour
streaking away from the Geminid radiant near Castor.
On December 12th, find a dark area and watch for Twins
throwing darts!

Geminid Meteor Shower
Radiant
GEMINI
Castor
ORION

Pollux

Looking East

S&T ILLUSTR ATION

Wasat is my star-hop gateway to something much deeper. To
locate it, I return to 27× and shift less than 2° east-southeast
to the 5th-magnitude star 63 Geminorum, then veer southeastward a further 2/3° to what seems like a faint, delicate
double star. The 8th- and 9th-magnitude points of light, 99″
apart, lie north-south. Oddly, the dim southern "star" looks
out of focus. I bump up to 50×, but every time I concentrate
on that fuzzy southern component, it disappears!
The finicky fuzz is a planetary nebula labelled NGC 2392.
The term "planetary nebula" is a centuries-old misnomer that
endures because in telescopes most of these nebulae appear
vaguely planet-like. In reality, a planetary nebula is the
ejected atmosphere of a dying star. Our specimen in Gemini
is a whopping 4,100 light-years from Earth yet highly photogenic. In certain images NGC 2392 resembles a human face
inside the fur-lined hood of a winter parka, an allusion that
years ago led to an evocative but archaic name: the Eskimo
Nebula. I prefer another popular moniker - the Clown Face
Nebula. One observer I know dubs it the Bozo Smudge!
NGC 2392 glows at magnitude 9.2, a full magnitude less
than the 8.2-magnitude star guarding it. Officially, it has
dimensions of 47″ × 43″, but in the scope at 50× it's essentially
a spherical blob punctuated by a 10th-magnitude central star
(the "nose" in the face). At 97×, the surrounding nebulosity
becomes a more obvious disc, provided I keep looking with

averted vision. As mentioned earlier, the fuzz totally disappears when I stare at the central star. Upping the power to
194× (and maintaining averted vision) greatly intensifies both
nebula and star. By the way, with each change of eyepiece, I
refocus on that convenient 8th-magnitude guardian star.
Observing NGC 2392 can be aided by a general lightpollution filter. Better yet are the popular Ultra-High Contrast (UHC) and doubly-ionized oxygen (O III) filters. When
the eyepiece in my little Newtonian is O III-equipped, the
central star and nearby guardian star are noticeably attenuated, and the background sky is dark. What remains is a
high-contrast nebula that actually outshines the guardian
star. Even so, a strongly filtered view at high magnification
can be difficult to appreciate if, like me, you're observing
amid illuminated city surroundings. All you can do is cover
your head, cup your hands around the eyepiece, and stare
(patiently) with averted vision. Hey, it works!

M A RTIN SCHOENBA LL

Best Foot Forward

S STELLAR CYCLOPS Backyard astronomers frequently compare NGC
2392 to the head of a clown or lion, but the illusion falls apart in larger
scopes. The view through a 10-inch f/5 reflector reveals a bright central
star surrounded by attenuating rings of nebulosity.

Back to the binoculars. From Wasat I sweep to the southwest,
encountering myriad stars as I go. That's because Gemini is
crossed by the Milky Way; its center line - the galactic equator - runs beneath the Twins' feet. I stop at Propus ("forward
foot") in the richest portion of the Gemini Milky Way. In
addition to Propus, the field includes Tejat and 1 Geminorum,
plus Gemini's brightest deep-sky object: the open cluster
Messier 35. About 2,800 light-years away, M35 is populated
with a few hundred young, blue-white suns that my binocus k y a n d t e l e s c o p e .c o m

* FEBRUARY 2017

61


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Sky and Telescope - February 2017

Table of Contents for the Digital Edition of Sky and Telescope - February 2017

Contents
Sky and Telescope - February 2017 - Cover1
Sky and Telescope - February 2017 - Cover2
Sky and Telescope - February 2017 - 1
Sky and Telescope - February 2017 - Contents
Sky and Telescope - February 2017 - 3
Sky and Telescope - February 2017 - 4
Sky and Telescope - February 2017 - 5
Sky and Telescope - February 2017 - 6
Sky and Telescope - February 2017 - 7
Sky and Telescope - February 2017 - 8
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