Sky & Telescope - March 2020 - 56

MARCH 2020 OBSERVING
Deep-Sky Wonders

(μ) Geminorum and only 11′ south
of the 7.3-magnitude star HD 44251.
I couldn't spot it with my 14.5-inch
reﬂector at 276× - until I added a
narrowband ﬁlter. Then, a little touch
of mist made its debut, resting on
the northeastern wing of a 10′ asterism that resembles a butterﬂy. HoCr 1
seems slightly elongated and about 35″
long, with a very faint star nuzzling the
northeastern end. Knowing what to
expect, I could then detect the nebula
using averted vision with the ﬁ lter
removed. In many images, the nebula
looks rather blocky.
Michael Howell discovered HoCr 1
on an image he made in early 2006.
Later that year, he began a collaboration with fellow narrowband-imager
Richard Crisp to identify it. Astronomer George Jacoby provided highresolution images and is listed as the
primary investigator in a 2010 paper in
Publications of the Astronomical Society
of Australia that includes this object.
Spectral data support its classiﬁcation
as a planetary nebula.

HD 44251
HoCr 1

IC 443

Jonckheere 900

Finally, we'll visit the planetary nebula Jonckheere 900. You'll ﬁnd it 1.5°
due west of the pretty double 20 Geminorum, whose components shine yellow
and yellow-white. J900 is easy to see
through my 105-mm refractor at 47×,
appearing stellar. At 122× it becomes
a tiny nebula with a star on its southsouthwestern edge. I tried some intermediate magniﬁcations, but star and nebula
blended together as one little blob.
Robert Jonckheere was one of the
leading double-star discoverers of the
20th century. Among his ﬁnds were
some nebulae and galaxies masquerading as double stars. In 1912 Jonckheere
announced that J900 is a 3″ planetary
nebula showing two stellar points
within. In 1917 Edward Emerson
Barnard wrote that with the 40-inch
Yerkes Observatory refractor, the nebula
spanned 7.9″ and was possibly a little
brighter in the east, but he saw no central condensation or stars. Jonckheere
replied that he'd seen three condensations in 1915, and he attributes the
difference in the nebula's apparent size
to the aperture of the telescopes. His
original estimate of 3″ was made with
a 12.8-inch refractor, and his 1915
estimate with a 28-inch refractor was
6.1″. The presence of knots in J900's
structure was later conﬁrmed photographically. What do you see through
the eyepiece of your telescope?
¢ Contributing Editor SUE FRENCH
wrote this column for the March 2014
issue of Sky & Telescope.

MARCH 2 02 0 * SK Y & TELESCOPE

IC 443: SE A N WA LK ER / S&T
J9 0 0: ESA / HUBBLE & N ASA / JOSH BA RRINGTON

the ﬁlter. It gently curves through a
shallow pan outlined by six stars. A
seventh star off the pan's southeastern
end adds a very short handle. This part
of IC 443 is called the Jellyﬁsh Nebula,
because in images it looks like a jellyﬁsh bell and has tentacles of nebulosity
trailing southwest.
IC 443 displays two sections when
viewed in my 10-inch scope at 44×,
with either a narrowband or an O III
ﬁlter. The northeastern arc appears
brightest. It's shaped like a fat parenthesis mark nearly ½° long, one-third as
wide, and concave toward the southwest. The section near Eta is much more
difﬁcult - I can only detect it as an
amorphous patch of light southeast of
the star and perhaps 12′ across.
German astronomer and astrophotography pioneer Max Wolf discovered
IC 443 and dimmer IC 444 to its eastnortheast with a 2¼-inch, portrait-lens
astrograph in 1892.
Not far from IC 443, the probable
planetary nebula Howell-Crisp 1
dwells 1.1° north-northwest of Mu

Sky & Telescope - March 2020

Table of Contents for the Digital Edition of Sky & Telescope - March 2020