OF THE ROGER N. CLARK

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M94 (NGC 4736), GALAXY IN CANES
VENATICI
R.A. 12h 51.0m, Dec. 4r 07' (2 000.0)
Technical. M94 is a violently active galaxy
with tightly wound spiral arms. Although it
looks rather normal, there is evidence of an
explosion that may have occurred as recently
as 10 million years ago. Some astronomers
speculate that all spiral galaxies have
periodic violent outbursts. Thus the so-called
violent galaxies may actually be quite normal.
(See also the description of MI06,
another of this class.)
VISUAL ASTRONOMY OF THE DEEP SKY
There are two sets of spiral arms. The inner
set contains many irregular dust lanes
which are usually lost in deep-sky photo :
graphs owing to overexposure. The Outer
arms are much fainter and rich in dust. A
ring of material beyond them extends 1 5 arcminutes
from the nucleus.
Visual. M94 appears at magnitude 8.9 and
has a size of 5.0 by 3.5 arc-minutes, yielding a
mean surface brightness of 20.6 magnitudes
per square arc-second. That size corresponds
to the faint outer arms, which may be un-
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bservable under most conditions. The
righter inner arms are about 2 by 1.5 arc-
inutes, and the mean surface brightness in
is region is a magnitude or more brighter.
t The high surface brightness helps in the
detection of detail in this galaxy. Through the
8-inch under only moderate skies and at powers
near 200 X, the inner spiral arms were
een as a ring surrounding the nucleus. The
ucleus is very bright compared to the arms,
but does not appear stellar, being 30 arcseconds
across.
A VISUAL ATLAS OF DEEP-SKY OBJECTS
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Photograph oJ M94. South is up . (Courtesy Palomar
Observatory.)
Drawing oJ M94.
Scale: 1.2 arc-min/cm
8-inch f/ 11.5 Cassegrain
12.5mm Orthoscopic
(187x)
Viewing Distance (cm)
25 X: 115 200 X: 14
50 X: 57 300X:l0
lOOx: 29 400X: 7
air mass: 1.31, faintest star: 13.3 at zenith, 188x;
no tracking
6/22/82 8:00-8: 15 UT at Hawaii Kai, Hawaii; R.
Clark
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