Sky & Telescope - January 2019 - 54

JANUARY 2019 OBSERVING
Deep-Sky Wonders by Sue French

Meridian
Observing
Viewing is at its best when
an object is at its highest in
the night sky.

JA N UA RY 2 019 * SK Y & TELESCOPE

p NGC 869 and NGC 884, together known as the Double Cluster, are approximately the same
age (14 million years old) and lie about the same distance (7,500 light-years) from Earth. These
measurements suggest that the two clusters formed in the same stellar nursery.

orange stars adorn the area, all variables. One of these vermillion jewels
(BU Per) hovers north of NGC 869, and
another (AD Per) rests in the southern reaches of the pair, about halfway
between the clusters. FZ Per colors
NGC 884's western outskirts, while
V0439 and V0403 Per shine in the eastnortheast. The smoldering ember RS Per
burns east-southeast of the sparse core.
The Double Cluster nearly bridges
the ﬁeld through my 10-inch scope at
68×, yet the view is astounding, with
each cluster ﬂaunting more than 100
stars. NGC 869's smile and nose gain a
pair of batlike ears to the north-northwest, the smiling bat covering about 3′.
Recent studies indicate the clusters
are not merely a line-of-sight coincidence. According
to a 2010 paper by
Thayne Currie and
colleagues in the
Astrophysical Journal
u The light from the open
cluster M34 takes about
1,500 years to reach
Earth. M34 lies about
halfway between the
stars Alpha (α) and Beta
(β) Persei.

Supplement Series, these youthful clusters are approximately 14 million years
old. Four different estimates loosely
place NGC 869 in a realm 7,650 lightyears away from us, but with NGC 884
systematically in the foreground by
about 176 light-years.
Also in Perseus, Messier 34 is an
odd-looking open cluster through
the 130-mm scope at 37×. The outer
boundary looks boxy, but with a
rounded southwestern corner. Bright
stars near the middle of the northern
and southern borders shine orange
and deep yellow, respectively. There's a
bizarre pattern of stars in the core, like
a bug-eyed guy running in terror with
his arms ﬂung wide. His eyes blaze a bit
northwest of the cluster's center, and
his bent legs stretch
southeastward. About
75 stars lodge within
½° of sky.
M34 was most
likely discovered by
Giovanni Battista
Hodierna, as mentioned in the text of
his 1654 De Admirandis Coeli Characteribus
(On the Admirable

DOUBLE CLUSTER: STOCK TREK IM AG ES / G E T T Y IM AG ES;
M34: SCOT T M ACNEILL

he celestial meridian is an imaginary line in the sky that runs due
north to due south and passes through
a point straight overhead. For those of
us in the Northern Hemisphere, the
wonders of the night sky are best witnessed when they traverse the meridian between Polaris and the southern
horizon. That's when they're highest in
our sky and least diminished by Earth's
atmosphere. This month's deep-sky tour
will showcase marvels berthed near the
meridian on the all-sky chart at the
center of this magazine.
Our ﬁrst stop is the outstanding
Double Cluster in Perseus, NGC 869
and NGC 884. The pair is easily seen
as a gauzy smudge to the unaided eye
from my semirural home. It was likely
familiar to the ancients, but the earliest
known record comes from the Greek
astronomer Hipparchus of Nicaea, who
lived during the second century BC.
The Double Cluster is breathtaking
through my 130-mm refractor at 48×.
NGC 869's central concentration holds
about 25 stars, including a U-shaped
group of ﬁve stars that looks like a big
smile with a bright nose star westnorthwest. At least 60 additional suns
plump out the cluster. NGC 884 is less
concentrated with only 10 or so stars
clumped in the core and about 70 stars
strewn around them. Together the clusters span nearly 1°, their edges blending
gradually into the background sky.
Most of the cluster stars gleam white
to blue-white, but some strikingly red-

Sky & Telescope - January 2019

Table of Contents for the Digital Edition of Sky & Telescope - January 2019