16 ASTRONOMY • JANUARY 2022
20 NGC 6231
Look toward the southern region of Scorpius
and you’ll encounter what seems to be a
brilliant comet. The head of this asterism,
known as the False Comet, is the spectacu-
lar NGC 6231. This is the sky’s sixth-brightest
open cluster, an object often called the
Northern Jewel Box because of its resem-
blance to the Jewel Box Cluster (NGC 4755;
see #40) in the southern constellation Crux.
NGC 6231’s apparent diameter is 15', half
that of the Full Moon, and it lies some 5,
light-years away.
Italian astronomer Giovanni Battista
Hodierna discovered NGC 6231 in 1654 and
included it on a list of nebulous objects that
observers might misinterpret as comets
(just as Charles Messier had 120 years later).
This object shines so brightly, however —
at magnitude 2.6 — that skywatchers earlier
than Hodierna certainly noticed it.
The area from Zeta (ζ) to Mu (μ) Scorpii
contains a group of young blue stars called
the Scorpius OB1 association. To our eyes,
some 20 members appear more luminous
than 9th magnitude. Up close, they would be
blinding. The brightest stars of the Northern
Jewel Box put out 60,000 times more light
than the Sun.
Although this cluster is an easy naked-
eye target that stands out well even from the
surrounding Milky Way star field, binoculars
will reveal half a dozen lesser open clusters
nearby. When you finish glancing at those,
point a 4-inch telescope back at NGC 6231
and you’ll see more than 100 stars strewn
across its ¼°-wide diameter. Crank up the
power and look at the center of this object
for a tight grouping of stars that outshine the
others. — M.B.21 The Saturn Nebula
The Saturn Nebula (NGC 7009) is a planetary nebula in the constellation
Aquarius the Water-bearer. While to a casual viewer its common name
may seem misplaced, it comes from the thin lobes on either end of its
disk. These projections, called ansae (Latin for “handles”), make this
nebula look like Saturn, complete with rings, in large scopes. The ansae
are actually gas that the nebula has ejected in opposite directions. This
fascinating object lies some 5,000 light-years away.
The Saturn Nebula resides slightly more than 1° west of the magnitude
4.5 star Nu (ν) Aquarii, or just slightly southeast of the midpoint of a line
from magnitude 2.9 Sadalsuud (Beta [β] Aquarii) to magnitude 3.1 Dabih
(Beta Capricorni).
Because NGC 7009 glows at magnitude 8, it’s easy to observe through
an 8-inch or larger telescope. Your best chance to unlock some details
is to use magnifications above 200x — or at least the highest that sky
conditions at your observing site allow.
First, try to spot the central star. This magnitude 11.5 point of light sits
at the center of NGC 7009. Once a hydrogen-fusing sun like our own, the
star is now a white dwarf.
Once you find the central star, take a look at the overall shape of this
planetary, which definitely appears oval. The long axis of the disk spans
25'. Each ansa protrudes from the disk another 2'. If you are viewing
through a 14-inch or larger scope, examine the ends of the ansae and
look for slightly fainter round regions. — M.B.
MICHAEL STECKERDAN CROWSON