Sky and Telescope - May 2017 - 49

C ring on
globe

Equatorial
zone

RINGS
A B C

Cassini
Division
Encke
Gap

North
Equatorial
Belt
North Polar Region

p Saturn's rings were tilted 25°, almost as
much as now, when Damian Peach took this
very sharp image on March 10, 2015, using a
planetary video camera on a 14-inch SchmidtCassegrain scope. South is up.

with a little more effort. Both the A and
B rings brighten toward their edges
bordering the Cassini Division.
The dusky C ring is more of a challenge where it appears against the
dark-sky background. It's often fairly
plain in my 12.5-inch but rarely in my
6-inch. Its dim gray veiling is easier
to see where it crosses Saturn's bright
face, just inside the B ring. Sometimes
the C ring in front of Saturn's face is
indistinguishable from the rings' dark
shadow falling at the same latitude. But
this season the rings'' shadow is hidden
behind the rings themselves.
The hair-thin Encke Gap, near the

outer edge of the A ring, is a severe
challenge under any conditions. I can't
say for sure that I've ever seen it with
my 12.5-inch even in excellent seeing.
With the rings wide open, you
have your best chance to see Saturn's
surface through the Cassini Division. In very steady air, detecting the
planet's light through the division - as
opposed to black sky behind the division
elsewhere - can emphasize the threedimensional appearance of the view.
For several nights around Saturn's
June 15th opposition, watch for the
Seeliger effect: a noticeable brightening of the rings with respect to the globe.
This is caused by the solid ring particles
"backscattering" sunlight in the direction it came from - the inner solar system, home of Earth - more effectively
than the planet's cloudtops do.
In the weeks and months away from
opposition, note the shadow of the
planet's globe on the rings. It's the
narrow black gap right where the rings
pass behind the globe's celestial west
(preceding) side before opposition, and
the east (following) side after opposition.

Marvelous Night
for a Moon Dance
Saturn and its rings are surrounded by
more moons for amateur scopes than
any other planet.
Even a 60-millimeter scope will
usually reveal Titan, a frigid, haze-

shrouded world half again as big as our
Moon. A 6-inch shows Titan's orange
color: Its haze is photochemical smog,
thick enough to hide Titan's rainclouds,
rivers, dark hydrocarbon mudﬂats, and
lakes of liqueﬁed natural gas.
A 4- to 6-inch scope will also show
Iapetus, Rhea, Dione, and (maybe with
difﬁculty) Tethys. Fainter Enceladus
closer in almost always eludes my
6-inch despite my best efforts, but the
12.5-inch ﬁshes it up when the seeing
is especially good. It helps to know in
advance precisely where a difﬁcult object
you're looking for ought to be. You can
identify the moons, or ﬁnd exactly
where to look for them, at any time and
date using the interactive observing aid
at skyandtelescope.com/satmoons.
Or for handy use at the scope, get our
SaturnMoons iTunes app from the
iTunes App Store ($2.99).

May Meteors
º The Eta Aquariid meteor shower runs for
several mornings centered on May 6th. The
time to watch is the hour before the first light
of dawn. The waxing gibbous Moon will then
be low in the west. The Eta Aquariids are
usually the year's best meteor shower for
the Southern Hemisphere. But those of us in
the world's mid-northern latitudes see few if
any, because the radiant, in the Water Jar of
Aquarius, is still low when dawn begins.

Midday Aldebaran Occultation
º If you have a deep blue sky on Friday,
April 28th, you have a shot at observing
a challenging daytime event from nearly
anywhere in the United States, Canada,
or Mexico. The 2-day-old waxing crescent Moon will be in the eastern sky,
about 30° lower left of the Sun, when
the Moon's dark limb occults 1st-magnitude Aldebaran. A telescope may show
the orange star, although daytime stars
can be tough when they're this close
to the Sun, especially when the Sun is
higher than they are.
The farther east you are the better.
In the Pacific time zone, the crescent

Moon may be too low to find in the
daytime sky. Seen from the Eastern time
zone, it'll be much higher.
If you find the Moon, you'll know
where to point your scope: Just east of
the crescent's invisible dark limb. Once
you're there, moderately high power
may work best for picking up Aldebaran.
Some times of its disappearance: Los
Angeles, 9:02 a.m. PDT; Denver, 10:11
a.m. MDT; Austin, 10:55 a.m. CDT;
Kansas City, 11:11 a.m. CDT; Chicago,
11:19 a.m. CDT; Miami, 12:07 p.m. EDT;
Atlanta, 12:08 p.m. EDT; Washington,
DC, 12:23 p.m. EDT; New York, 12:28

p.m. EDT; Boston, 12:35 p.m. EDT.
In Western Europe the occultation
happens in better circumstances: during
late afternoon or in evening twilight, with
the Moon now higher than the Sun.
Precise time predictions, and altitudes
of the Sun and the Moon at the moment
of occultation, are listed for over 1,000
cities and towns at lunar-occultations.
com/iota/bstar/0428zc692.htm. (That
page displays three long tables with
less-than-obvious divides: for the disappearance, the reappearance, and the
locations of cities. The two-letter abbreviations are for countries, not states.)
s k y a n d t e l e s c o p e .c o m

* MAY 2017

http://www.skyandtelescope.com/satmoons http://lunar-occultations.com/iota/bstar/0428zc692.htm http://lunar-occultations.com/iota/bstar/0428zc692.htm http://www.skyandtelescope.com

Sky and Telescope - May 2017

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