1°SCULPTORePath of Comet CatalinaNEb+fg
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611162126July 1Comet Catalina (C/2013 US10)1'
June 8, 11:00 P.M. EDTSaturnRheaEnceladusTethysDioneTitanIapetusSWThe ringed world’s menagerie of moons42 ASTRONOMY • JUNE 2015
down, and with Jupiter visible
for only a few hours each night,
North American observers can
see only a half dozen or so
during June.
A nice event visible from
the continent’s eastern half
occurs as darkness falls June 3.
Ganymede eclipses Io for 28
minutes starting at 9:43 p.m.
EDT. Io shines only three-
quarters of its normal bright-
ness at mideclipse. Ganymede
— the solar system’s largest
moon — adds extra spice by
appearing in transit across the
planet’s disk during the event.
Io begins to transit Jupiter at
10:47 p.m. EDT followed by its
shadow at 11:56 p.m. Just one
minute after that, Ganymede
clears the gas giant’s disk. The
size when viewed through a
telescope shrinks only 2 per-
cent. Saturn’s higher altitude
and better visibility during the
evening hours easily make up
for these minor losses.
The solar system’s second-
largest planet is set against
the faint backdrop of eastern
Libra, though it’s not far from
the riches of Scorpius. It lies a
bit more than 10° northwest ofCOMETSEARCH
Will the comet gods deliver on
their next promise? Astrono-
mers predict that Comet Cata-
lina (C/2013 US10) will be visible
to the naked eye late this year.
Observers have a chance to
catch a preliminary view of this
visitor from the Oort Cloud
during June as it dives south
through Sculptor.
This constellation hangs low
in the southeastern sky shortly
before morning twilight begins.
(Observers in the Southern
Hemisphere can find Sculptor
just below 1st-magnitude
Fomalhaut as it climbs in the
eastern sky after midnight.)
Comet experts expect Catalina
to be glowing around 8th or 9th
magnitude in June. The comet
should look nearly round at this
stage, though its northeasternflank will look slightly more
defined where solar radiation
pushes against the comet’s
dusty envelope.
Northern Hemisphere view-
ers will have to wait for Catalina
to make a long sojourn through
the southern sky before it
returns to view in late November.
By then, the comet could be
glowing at 4th or 5th magnitude
as it shares the morning sky
with Venus. It then will cruise
past magnitude 0.0 Arcturus as
the calendar ticks over to 2016.
Astronomers with the U.S.-
based Catalina Sky Survey dis-
covered the comet October 31,- The designation “US” in its
official name comes from the
chronological order of its dis-
covery, however, and not the
country of those who found it.
Catalina scrapes the predawn horizon
EVENING SKY MIDNIGHT MORNING SKY
Venus (west) Saturn (south) Mercury (northeast)
Jupiter (west) Uranus (east)
Saturn (southeast) Neptune (southeast)
WHEN TO VIEW THE PLANETS
— Continued from page 37
big moon’s shadow, which
got this whole affair started,
touches the jovian cloud tops
beginning at 12:58 a.m. EDT,
after Jupiter has set for East
Coast observers.
Perhaps the best event for
those living in western North
America occurs the evening of
June 10. Ganymede occults Io
from 9:55 to 10:18 p.m. PDT
while both moons are transit-
ing Jupiter.
As Jupiter descends in the
western sky, Saturn climbs in
the east. Although it reached
opposition and peak visibility
in late May, the ringed planet’s
appearance hardly suffers in
June. It dims almost imper-
ceptibly this month, from
magnitude 0.1 to 0.2, and its1st-magnitude Antares, the
Scorpion’s brightest star. The
Moon appears Full when it
passes near Saturn the eve-
ning of June 1 and shows a
bright gibbous phase when it
returns on the 28th.
A telescope turns Saturn
from a steadily shining point
of light into a wondrous
ringed world. In mid-June,
the planet’s globe measuresA possible naked-eye object late this year, Comet Catalina should glow at
8th or 9th magnitude in June as it chisels its way south through Sculptor.All of Saturn’s bright moons appear near the planet the evening of June 8,
including distant Iapetus, which then lies due north of the gas giant.