SkyandTelescope.com March 2014 57Sue French welcomes your comments at [email protected]. Sue French
Ferrero 18HoCr 1μ ην1χ^221292158M352174-5IC 443J900GEMINIHD 4425120ORION6 h 10 m 6 h 00 m+24°6 h 30 m 6 h 20 m+22°+20°+18°Star magnitudes5436
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9Star Groups and Nebulae in the Celestial Twins
Object Type Mag(v) Size RA Dec.
M35 Open cluster 5.1 28′ 6 h 09.0m +24° 21 ′
NGC 2158 Open cluster 8.6 8 ′ 6 h 07.4m +24° 06 ′
NGC 2129 Open cluster 6.7 7 ′ 6 h 01.1m +23° 19 ′
Ferrero 18 Asterism — 17 ′ 6 h 15.4m +25° 30 ′
IC 443 Supernova remnant 9 50 ′ × 40 ′ 6 h 16.8m +22° 31 ′
HoCr 1 Probable planetary nebula — 73 ′′ × 59 ′′ 6 h 21.7m +23° 35 ′
J900 Planetary nebula 11.7 9′′ 6 h 26.0m +17° 47 ′
Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than
the cataloged value and varies according to the aperture and magnifi cation of the viewing instrument.
Right ascension and declination are for equinox 2000.0.In my 130-mm refractor at 37×, M35 shows about 65
mixed bright and faint stars in the core group, which has
ragged edges and spans roughly 25′. I can imagine yet
another mushroom, with its cap pointing west, formed
from the brightest stars of the core. Outliers stretch
the cluster to 40′ and extend as far as NGC 2158. M35’s
brightest gem is the topaz primary of the double star ΟΣ
134, while the companion star to the south is a pale sap-
phire. Although M35 is mainly adorned with blue-white
stars, a few shine golden yellow, as does the lovely beacon
off the cluster’s eastern side. With a wide-fi eld eyepiece
giving a true fi eld of 58′ and magnifi cation of 102×, M35
is a stunning jewel box.
NGC 2158 shares the fi eld of view with its fl ashy
cousin, but it’s much farther from us — and certainly
looks it! In the 37× view described above, NGC 2158 is
merely an 8′-wide glow with three superimposed stars: a
pair northeast and a brighter star south-southeast of the
cluster’s center. The cluster is very pretty at 102×, showing
perhaps a dozen members stippling the haze. The faint-
ness of the stars is testament to their distance of 16,500
light-years, six times farther away than the suns of M35.
Philippe Loys de Chéseaux is generally credited with
the discovery of M35. He included it in a list of 20 nebulae
and star clusters that he compiled in the years 1745 and- Among the objects that de Chéseaux deemed ordi-
nary star clusters, it was simply listed as the one above
the northern feet of Gemini. Despite its proximity to
such a well-known object, NGC 2158 wasn’t found until - Discoverer William Herschel called the cluster a
miniature of M35 in his Catalogue of One Thousand New
Nebulae and Clusters of Stars.
Other enticing objects surround M35, among them
NGC 2129. This cluster is an easy fi nd 42′ east of the
yellow, 4th-magnitude star 1 Geminorum in Castor’s
northwestern foot. Through my 105-mm refractor at 127×,
it packs two bright and about 20 faint to very faint stars
into a parcel of sky 7′ across. The cluster is very pretty
in my 10-inch refl ector, which shows half again as many
stars. William Herschel discovered NGC 2129 just before
NGC 2158 on the same night.
A nice asterism known as Ferrero 18 sits 1.9° north-
east of M35. In my 130-mm scope at 63×, the group
includes the northeastern corner of a prominent square
outlined by several fi eld stars. The square’s southeastern
corner is occupied by a yellow-orange, 7th-magnitude star
at the asterism’s southern edge. I count 24 stars loosely
scattered within 18′. In the view through his 8-inch refl ec-
tor at 71×, Finnish observer Jaakko Saloranta thinks the
group looks a bit like the constellation Scorpius.
Ferrero 18 was found by French amateur Laurent Fer-
rero during his search for uncataloged star clusters.
Our next target is the elusive supernova remnant IC
443. Its position is easy to pinpoint, because the bright
star Eta (η) Geminorum marks its western edge. With
my 130-mm refractor, I’ve only seen the nebula’s bright-
est arc, which lies 45′ east-northeast of the star. Its gauzy
profi le is faintly visible at 37× with an O III fi lter or at 63×
without the fi lter. It gently curves through a shallow pan
outlined by six stars. A seventh star off the pan’s south-DSW layout.indd 57 12/17/13 2:51 PM