NGC 7000 looks as big as a
continent — the continent of North
America, to be exact. This emission
nebula lies near Deneb in the tail
of Cygnus. It is 2° by 12/3° across, or
10 times the area of the Full Moon.
William Herschel discovered it, but it
was cataloged by his son, John. They
both saw the shape as indistinct,
combined with abundant stars in
the Milky Way. German astronomer
Max Wolf photographed the area
in 1890 and named it the North
America Nebula. NGC 7000 is part of
a larger complex — Sharpless 2–117
— that includes the Pelican Nebula
(IC 5070) and the swath of dark dust
that separates the two, named L935
by Beverly Lynds in 1962.
Edwin Hubble proposed that
the hot, luminous star Deneb was
responsible for ionizing the North
America Nebula’s gas, making it
glow. However, at a mere 14,840
degrees Fahrenheit (8,230 degrees
Celsius), Deneb is not hot enough.
It’s also too far from the nebula.
Instead, the nebula’s real energy
source — the star J205551.3+435225
— is five times hotter than Deneb.
It lies between the North America
and Pelican nebulae, embedded
within L935. That dark nebula dims
the spectral type O3.5 star by 9.6
magnitudes; it would otherwise be
one of the brightest stars in Cygnus.
For Northern Hemisphere
observers, Cygnus lies in the bright
patch of Milky Way visible in the late
summer and autumn skies. Withinthat, the North America Nebula is
bright enough that, in theory, it could
be seen with the naked eye under
perfect skies. With very good condi-
tions, the right binoculars will show
it as a large, amorphous glow 3° eastof Deneb. In a 4- or 6-inch rich-field
telescope with a wide-field eyepiece,
the nebula fills the field of view.
The Atlantic Coast and Florida are
its most distinct features, thanks to
their contrast with the adjacent darknebula. Mexico is less conspicu-
ous and the West Coast blends into
the rich Milky Way star field. UHC
filters really bring out the nebula,
while reducing the glare from the
foreground stars. — A.G.101 SKY OBJECTS
Among the planetary nebulae in the high north-
ern heavens, M97, the Owl Nebula, is the most
famous. Pierre Méchain discovered it on Feb. 16,
1781, about 2.5° southeast of Merak (Beta [β]
Ursae Majoris), noting it was difficult to see
with crosshairs illuminated. Messier agreed,
recording, “its light is faint.” The difficulty is not
so much its brightness (magnitude 9.8), but
that its dim light is spread across nearly 3.5' of
sky. Nevertheless, today the Owl is one of the
most sought-after planetary nebulae in the sky,
mainly because it presents observers with a
challenge: literally seeing eye-to-eye!
The “owl” moniker comes from a sketch
made in 1848 by William Parsons, Earl of Rosse,
through his 72-inch Birr Leviathan reflector,
which shows the round nebula’s curious eye-
like hollows. With a star in each socket, these
eyes seem to peer out from a face similar to
that of a barn owl. Lord Rosse wrote that the
stars were “considerably apart in the central
region” and surrounded by a “dark penumbra.”
Small-telescope users can infer the Owl’s eyes
at moderate magnifications by sweeping theirgaze back and forth across M97’s softly glowing
circular disk, which shines with a pale gray pal-
lor. Switch to high power (350x and greater) to
search for the two dim stellar pupils.
Lying some 2,600 light-years distant, this
planetary nebula sports a classical circular
planetary shape with a complex structure
consisting of three concentric shells: a faint
outer halo, a circular middle shell, and a roughly
elliptical inner shell. These shells were expelled
from its dying Sun-like star beginning some
6,000 years ago. First, normal stellar winds
created the outer shell after fusion in the par-
ent star’s core ceased. Then the star began
shedding its mass very quickly in a superwind,
which drove even more gas and dust outward
to form the middle shell. Finally, an even faster
stellar wind compressed the superwind to form
the inner shell and a bipolar cavity — a barrel-
like component oriented at an angle 45° to the
line of sight whose matter-poor tips create the
Owl’s eyes. If you have trouble perceiving the
eyes, try instead for the dim bar of light that
STEVEN MYATT separates them. — S.J.O.JASON WARE38 The Owl Nebula
39 North America Nebula