SKYTHIS
MONTH
Visible to the naked eye
Visible with binoculars
Visible with a telescope
MARTIN RATCLIFFE and ALISTER LING describe the
solar system’s changing landscape as it appears in Earth’s sky.
May 2018: Jupiter shines brilliantly
Dark cloud belts alternate with brighter zones in Jupiter’s atmosphere.
Even small telescopes will reveal details within these bands, particularly
when the gas giant looms large at its peak in May. NASA/ESA/A. SIMON (GSFC)
J
upiter rules the sky from
dusk to dawn. The king of
the planets reaches oppo-
sition and peak visibility
May 8, though it’s a star
attraction all month. The giant
planet has plenty of company,
however. Venus entertains
us during the early evening
hours, while Mars and Saturn
stand out after midnight. It’s
a cornucopia of planetary
delights that promises to thrill
every observer.
Let’s start our tour in the
western sky shortly after sun-
set. Venus shines at magnitude
–3.9 and appears beautiful
against the backdrop of bright
stars typically associated with
winter. On May 1, the planet
lies in Taurus about 5° north of
the Hyades star cluster and 10°
east of the Pleiades (M45). The
stars of Orion add to the stun-
ning scene as they sink toward
36
A ST R O N O M Y • MAY 2018
the western horizon along
with Venus.
Venus treks eastward as
May progresses, arriving at
a point midway between the
Bull’s horns (Beta [β] and
Zeta [ζ] Tauri) on the 13th.
Four days later, a wafer-thin
crescent Moon stands 6° to
Venus’ left. Our satellite
appears only 9 percent lit
because it passed between the
Sun and Earth just two days
earlier. Venus, on the other
hand, lies on the far side of
its orbit, and a telescope
reveals a 12"-diameter disk
that is 84 percent lit.
Venus continues its east-
ward sojourn all month. It
crosses into Gemini on
May 19 and passes less than
1° north of the 5th-magnitude
star cluster M35 on the 20th.
By month’s end, the planet
resides in central Gemini.
As twilight deepens, Jupiter
appears low in the east. On
May 1, it rises by 8:30 p.m. local
daylight time and achieves the
same altitude as Venus (though
on the other side of the sky)
around 9:20 p.m.
Jupiter reaches opposition
May 8, when it lies opposite
the Sun in our sky and
remains visible all night. This
peak coincides with the plan-
et’s closest approach to Earth,
so it shines brightest and
appears largest through a tele-
scope. But as an outer planet,
Jupiter changes slowly — it
shines brilliantly at magnitude
–2.5 all month, and its equato-
rial diameter stays between
44" and 45".
The planet’s steady appear-
ance is reflected in its slow
motion across the sky. Jupiter
resides in Libra, beginning
May 4° east of Zubenelgenubi
(Alpha [α] Librae) and ending
the month 0.9° northeast of
this 3rd-magnitude star.
For the best views through
a telescope, wait for the planet
to climb 30° high so its light
traverses less of Earth’s
image-distorting atmosphere.
It reaches this altitude around
midnight local daylight time
in early May and by 10 p.m. at
month’s close. These prime
viewing conditions last about
three hours.
Even the smallest instru-
ment reveals Jupiter’s two
dark equatorial belts, which
sandwich a brighter zone that
coincides with the planet’s
equator. More details pop into
view during moments of good
seeing, when Earth’s atmo-
sphere steadies, or when
observing through larger
scopes. Look for a series of
alternating belts and zones
that extends to the polar
regions. Also focus on fea-
tures along the turbulent
edges of the dark belts.
Because the planet spins on
its axis in less than 10 hours,
Jupiter at its best
Arcturus
VIRGO
Spica
C ORVUS
Jupiter
OPHIUCHUS
LIBR A
Antares
SC OR PIUS
10°
May 8, 11 P.M.
Looking southeast
The solar system’s largest planet peaks at opposition May 8, but it rules
the background stars of Libra all month. ALL ILLUSTRATIONS: ASTRONOMY: ROEN KELLY