dTAURUS
PleiadesPath of Comet PANSTARRSSept 1Oct 1211132330.5°NEComet PANSTARRS (C/2015 ER61)30"
September 17, 11:00 P.M. EDTSaturnIapetusTitanTethysRhea DioneMimasEnceladusWSSpotlight on two-faced Iapetus42 ASTRONOMY • SEPTEMBER 2017
COMETSEARCH
Although the brighter comets of
spring may be gone, the plea-
sures of viewing fainter comets
from a dark site at this time of
year shouldn’t be overlooked.
First, you get to see the magnifi-
cent Milky Way emerge out of
the dusk; then, the Cygnus star
clouds take over at midnight;
and finally, the sparkling stars
of winter splash across the sky
before daybreak.
Comet PANSTARRS (C/2015
ER61) enjoys the company of
one of winter’s finest star clus-
ters. The comet remains within
3° of the Pleiades (M45), or
Seven Sisters, throughout
September. The month begins
with a few Moon-free mornings,
when the comet and cluster ridehigh in the southeast. A second
window opens once our satellite
wanes to a slim crescent in mid-
September. For the rest of the
month, you can view the comet
starting around midnight local
daylight time and continuing
until it passes nearly overhead
before morning twilight begins.
This 10th-magnitude comet
shadows the Pleiades all month.
It begins September nearly
due east of the cluster, then
heads slowly east before revers-
ing course and moving more
quickly to the south and west.
Experienced observers won’t
have trouble viewing PANSTARRS
through a 4-inch telescope, but
you might need a 6- or 8-inch
instrument to see fine details.Cruising past the Seven Sisters
EVENING SKY MIDNIGHT MORNING SKY
Jupiter (west) Uranus (southeast) Mercury (east)
Saturn (south) Neptune (south) Venus (east)
Neptune (southeast) Mars (east)
Uranus (southwest)
Neptune (west)
WHEN TO VIEW THE PLANETS
— Continued from page 37
rings. The mission comes to
an end when the spacecraft
plunges into Saturn’s atmo-
sphere September 15.
Take your time observing
Saturn before turning your
attention to Neptune. This ice
giant world reaches opposition
the night of September 4/5,
when it lies opposite the Sun in
our sky and thus remains vis-
ible all night. You can find it
climbing in the southeastern
sky after darkness falls. It
peaks in the south around
1 a.m. local daylight time in
early September and by 11 p.m.
late in the month.
For an outer planet, opposi-
tion typically coincides with
best visibility. But on the eve-
nings of the 4th and 5th, the
Full Moon lies near Neptune
which measures 2.4" across and
appears blue-gray.
Uranus tracks across the
sky a couple of hours behind
Neptune. You can start to look
for Uranus once it climbs clear
of the eastern horizon in late
evening. It glows at magnitude
5.7, making it an easy binocu-
lar target and visible to the
naked eye under a dark sky.
Uranus resides among the
background stars of Pisces, notand makes viewing difficult.
Fortunately, the planet shines
at magnitude 7.8 all month, so
you can find it with equal ease
on any clear night.
Grab your binoculars and
center 4th-magnitude Lambda
(λ) Aquarii in your field of
view. In early September,
Neptune lies 1.2° due east of
Lambda. The planet’s west-
ward motion brings it 0.7°
southeast of the star by
month’s end.
Neptune passes just 1'
south of an 8th-magnitude
background star the night of
September 18/19. Although the
similarly bright objects may be
hard to identify through bin-
oculars, a telescope will tell
you which is which. Only
Neptune shows a distinct disk,far from 4th-magnitude
Omicron (ο) Piscium. The
planet stands 1.0° north of
this star September 1 and
moves to a point 1.2° north-
west of it by the 30th. A
telescope reveals Uranus’
distinctive blue-green disk,
which spans 3.7".
You’ll have to wait until
early morning to catch sight
of the inner planets. Venus
appears first, rising in a darkThis comet should glow around 10th magnitude during September
as it lingers just a few degrees southeast of the Pleiades star cluster.Saturn viewers can zero in on Iapetus the evening of September 17,
when the dim moon lines up with brighter Titan and the ringed planet.