WWW.ASTRONOMY.COM 47(Delta [δ] Corvi), or 11° west of Spica
(Alpha Virginis).
The Sombrero Galaxy’s lens shape and
the dark dust lane that splits it are easy to
spot. What’s more, the galaxy’s two sec-
tions have unequal brightnesses — the
north outshines the south because M104
inclines 6° to our line of sight. The dust
lane, therefore, appears to cross a bit south
of center from our perspective.
Through a 4-inch telescope, you may
detect the dust lane, but only near the
Sombrero’s center. The core is bright, and
a large halo surrounds it. It even extends
above and below the sections of the spiral
arms nearest the nucleus.
M101
Only one thing prevents spiral galaxy
M101 from making every observer’s top
10 list: its surface brightness. Covering
slightly more area than the Full Moon,
M101’s light spreads out so much that only
large amateur telescopes (those 12 inches
and larger in aperture) do it justice. That’s
not to say you can’t see it through smaller
scopes; I just want you to reduce your
expectations a bit.
M101 represents one of the sky’s
“grand design” spiral galaxies — one
with prominent and clearly defined spiral
arms. Usually, the arms mostly or com-
pletely envelop such galaxies. Only about
10 percent of all spiral
galaxies fall into the
grand design
category.
This wonderful
object lies in the
constellation Ursa
Major. To get a
rough idea of its
position, make the
base of an equilateral
triangle with the end
two stars of the Big
Dipper’s handle; M101
marks the triangle’s third
point above. Alternatively, it lies 1.5° east-
northeast of the magnitude 5.7 star
86 Ursae Majoris. M101 glows at magnitude
7.9 and has a diameter of 40'.
From a dark site through a large telescope,
look for M101’s multiple spiral arms. The
core is concentrated but broad, not starlike.
Many star-forming regions and stellar asso-
ciations (loose open clusters) lie along M101’s
spiral arms. In fact, at least five — NGC 5447,
NGC 5455, NGC 5461, NGC 5462, and
NGC 5471 — are bright enough to have their
own NGC numbers. Of these, NGC 5447 is
the most prominent. Find it 6' southwest of
M101’s core. Several other objects within
M101 once carried catalog designations, but
astronomers no longer recognize them. Usea nebula filter to tell the difference
between star-forming regions and
associations. The filter will dim the
stars within the associations, but not the
nebular gas of the star-forming regions.
This technique will help you see the
glowing hydrogen clouds better.NGC 5128
One note about the objects as they
appeared in The Outer Limits: StartingMICHAEL SIDONIOADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONANGC 5128
M101