10°PEGASUSAQUARIUS CAPRICORNUSAQUILASAGITTARIUS
AltairEnifFomalhautSaturn JupiterMarsLate May, 3:30 A.M.
Looking southeastURSA
MAJORDRACO
Path of
Comet
PanSTARRSMay 1
6
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31_h23
olM82NEM81k2°42 ASTRONOMY • MAY 2020
Morning planets (^)
COMET SEARCH I Peaking near a cigar
opposition, and a telescope will
reveal its growing apparent
size. During May, it expands
from 41" to 45", just 5 percent
shy of its opposition peak.
The dramatic display of
atmospheric belts and zones are
Jupiter’s main attraction. Most
obviously, a pair of dark equa-
torial belts straddle Jupiter’s
equator. Other features are
more delicate, however, and the
dazzle of the planet can drown
them out for casual observers.
Let your eye become accus-
tomed to its brilliance for a
minute before seeking out finer
details. The view of Jupiter is
exquisite when our turbulent
earthly atmosphere calms for a
second or two and enables a
beautiful spacelike view of the
solar system’s giant planet.
In addition to the appeal of
the cloud belts, Jupiter’s four
Galilean moons offer an ever-
varying display, including
occultations, eclipses, and tran-
sits. Individual events occur
throughout May, and occasion-
ally dual events occur within
minutes of each other. One
such back-to-back display
occurs the morning of May 3,
when Callisto casts its large
shadow onto Jupiter’s northern
temperate cloud tops as
Ganymede begins to disappear
behind the same limb, south of
the southern equatorial belt. As
Jupiter rises, Callisto’s shadow is
already on the jovian disk while
Callisto itself lies to the east of
the planet. Ganymede lies west
of Jupiter, and during a couple
of hours, Callisto’s shadow
nears the western limb of
Jupiter while Ganymede
approaches. Both events occur
almost simultaneously at
4:49 a.m. CDT (in the eastern
time zone, it’s already twilight,
though the event is still observ-
able). Ganymede’s disappear-
ance takes just seven minutes,
while Callisto’s shadow ambles
off the disk over the course of
20 minutes. This is because
Callisto is in a wider, slower-
moving orbit — illustrating the
laws of planetary motion.
On May 6 and May 22, Io
and its shadow traverse the
jovian disk. And a notable
trifecta of events occurs the
morning of May 21, when
Ganymede itself and Europa’s
shadow are both visible soon
after 2 a.m. CDT before being
joined by a transiting Europa
at 3:23 a.m. CDT.
Before moving on to Saturn,
it’s worth pointing out that
Pluto sits just 2.1° west of
Jupiter throughout May. But at
magnitude 14.7, you’ll need a
large scope and ideal viewing
SKY THIS MONTH
HIGHLIGHT OF THE YEAR:
Comet PanSTARRS (C/2017 T2)
shares a low-power field with the
Cigar Galaxy (M82)! As ideal as
modest-telescope comets get,
PanSTARRS hits a peak bright-
ness of 8th or 9th magnitude
while sailing high in the northern
sky. The comet makes its closest
approach to the Sun, or reaches
perihelion, May 4, at a distance
of 149 million miles. On the plus
side, PanSTARRS crests near
Polaris, making it accessible to
northern observers all night.
New Moon occurs May 22,
which is perfect timing because
PanSTARRS lies only ¾° from
M82 the following weekend.
PanSTARRS is just barely visible
with binoculars; it will show up
better in a 4-inch scope, and will
likely sport some green when viewed through a 12-inch scope.
From May 24 to May 26, make sure to look for a double-spike. The comet’s short, fan-shaped tail flat-
tens to edge-on when Earth passes through the orbital plane, so as long as our visitor from the Oort Cloud
produces a decent amount of both gas and dust, we can expect to see a green or blue streak on the lead-
ing edge and an “anti-tail” knife blade of white on the other. If you can, take a peek every other night to
catch the whole transformation. For the rest of the apparition we get more and more of a top-side view.
Comet PanSTARRS (C/2017 T2) (^)
— Continued from page 37
A trio of planets — Mars, Jupiter, and Saturn — will grace the southeastern sky
a few hours before sunrise this month.
EVENING SK Y
Mercury (northwest)
Venus (northwest)
MORNING SK Y
Mars (southeast)
Jupiter (south)
Saturn (south)
Uranus (east)
Neptune (east)
WHEN TO
VIEW THE
PLANETS
It takes roughly 15 minutes for light from the comet to reach us, but about
12 million years for light from the Cigar Galaxy to get here.