WWW.ASTRONOMY.COM 53Switch to a low-power, wide-
field eyepiece to enjoy our next
object. NGC 1981 is a coarse,
scattered open cluster contain-
ing 20 stars that glow with a
combined magnitude of 4.2.
The brightest three lie in an
arc. Add in a fourth star just to
the east, and the arc becomes a
pyramid of sorts. Several
fainter points offset to the west
also belong to the group, bring-
ing the total number of stars
visible through my 8-inch
scope to 17 across a 25' field.
Among the mighty Hunter’s
most interesting double and
multiple stars is none other
than Rigel (Beta [β] Orionis),
the constellation’s brightest star
and seventh brightest in the
entire sky. Rigel shines at mag-
nitude 0.3 and is cataloged as a
spectral type B supergiant. It
appears so dazzling through
telescopes that many people
miss its faint bluish companion
lying 9" to the south-southwest.
Rigel B is only magnitude 6.8,
400 times fainter than the pri-
mary. A 4-inch or larger scope
at high power will do the trick
on nights of steady seeing.
Mintaka (Delta [δ] Orionis),
the westernmost belt star, is
an easier catch.
Even binoculars
can show that the
2nd-magnitude
primary star is
accompanied by a
7th-magnitude
companion 52" due
north. Try studying
them at different
magnifications
through your
telescope. Can you
see a difference in
their colors?
Rivaling the
Trapeziu m as t he
finest multiple star
in Orion is Sigma
(σ) Orionis, just
south of the
easternmost belt star
Alnitak (Zeta [ζ]Orionis). The primary (Sigma A)
shines at magnitude 3.8. It is
separated from 5th-magnitude
Sigma B by only 0.25", making a
real challenge for any backyard
astronomer. Of the rest,
10th-magnitude
companion Sigma
C is the closest,
about 11" to the
southwest. At 7th
magnitude, Sigma
D lies 13" to
the northeast,
while the most
removed member,
6th-magnitude
Sigma E, is 42" to
the east. Can you
spot all five stars in
this group?
The area around
Alnitak teems with
interstellar clouds.
The brightest is the
Flame Nebula
(NGC 2024). My
8-inch scope shows
this patch as abright, oval glow with little sur-
face detail. Can you see the dark
dust band bisecting this object?
IC 434, a thin strip of emis-
sion nebulosity, extends more
than a degree south of Alnitak.
Due to its long length and low
surface brightness, IC 434 is a
difficult find for backyard
observers. The brightest por-
tion is visible near Zeta, its
exciting star, but it quickly
fades away as one scans
southward.
Near the middle of IC 434 is
the famous Horsehead
Nebula (Barnard 33). This
cloud of tiny, cold dust granules
spans about a light-year. We see
it only because it is silhouetted
against the glow of IC 434.Orion’s Belt contains three
brilliant stars — Alnitak,
Alnilam, and Mintaka — that
stand out as beautiful naked-
eye mileposts. The Horsehead
Nebula appears at left, south
of Alnitak. ROGELIO BERNAL ANDREO