Sky and Telescope - May 2017 - 47

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dimmer Theta (θ) Virginis and closer to
Gamma (γ) Virginis, the famous double
star also called Porrima.
Saturn rises at almost exactly the
same time Jupiter transits due south, a
little before 11:30 p.m. daylight-saving
time as May begins, a little before 9:30
p.m. as May ends. Saturn itself transits
around 4 a.m. in early May and around
2 a.m. in late May. Saturn will reach
opposition on June 15th, but it's already
quite prominent in the sky this month,
brightening from magnitude +0.3 to
+0.1. Its globe grows slightly, from 17.8″
to 18.3″ in equatorial diameter. The
rings span about 41″ in their long axis,
remaining at virtually their most open,
26° from edge-on.
Saturn is retrograding now, leaving
Sagittarius for Ophiuchus in the second
half of May.

DAW N
Venus comes up near the start of May's
very early morning twilight. Venus is at
its greatest morning brightness for the
year - or, more precisely, maximum
illuminated extent - on April 30th and
reaches greatest elongation, 46° west
from the Sun, on June 3rd. It dims a bit

Uranus
March
equinox

Jupiter

Mercury
Saturn

Neptune

Earth

30 minutes after sunset

ORBITS OF THE PLANETS
The curved arrows show each planet's movement during May. The outer planets don't change
position enough in a month to notice at this scale.

this month, from a bracing -4.7 to a
still impressive -4.5. The view of Venus
in telescopes remains fascinating: The
planet's apparent diameter decreases
from 38″ to 25″ while its disk increases
from about ¼ to nearly ½ lit. Will you
see Venus give the appearance of being
exactly half-lit by the end of May or in
the ﬁrst days of June? The ecliptic tilts at
a shallow angle to the horizon at spring
sunrises, so even as Venus nears greatest
elongation, it appears only about 23°
high at sunrise for viewers around latitude 40° north.
Mercury escapes observation this
month, lost in the glare of sunrise.

1 hour after sunset
Denebola

LEO
Moon
May 27

Sickle

Moon
May 31

aGem
Mars

cTau
Moon
May 26

Looking West-Northwest

Venus
June
solstice

Dusk, May 30-31

Dusk, May 26 -28

Sept.
equinox

Sun

Castor

Pollux
Moon
May 28

Mars
December
solstice

Regulus
Moon
May 30

Looking West, halfway up

Neptune, 8th magnitude, remains
in Aquarius and is high enough to spot
with a small scope just before morning
twilight. Uranus reappears in the dawn
sky in early May, but isn't well placed
for viewing.

M O O N PAS SAGE S
The waxing gibbous Moon is some 3°
to 5° right of Regulus on the evening
of May 3rd. At nightfall on May 7th,
the Moon beams about 3° lower left of
Jupiter and 9° above Spica. The waning
gibbous Moon shines 7° or 8° right of
Saturn at dawn on May 13th and 5° or
6° upper left of Saturn on May 14th.
Seek the waning lunar crescent approximately 4° lower right of Venus at dawn
on May 22nd, and well below Venus the
next morning.
Back in the evening twilight, the
waxing lunar crescent bows lower right
of Mars very low in the west-southwest
on May 26th. Mars that evening is
between Beta and Zeta (ζ) Tauri, the
horn-tips of departing Taurus; use binoculars. On the 29th, the waxing lunar
crescent hangs 3° lower left of M44,
the Beehive Cluster. On May 30th, the
thicker Moon hangs 8° lower right of
Regulus. By next night, the ﬁrst quarter
Moon has moved about 5° left of the
same star.
¢ Contributing Editor FRED SCHAAF
welcomes your letters and comments at
fschaaf@aol.com.
s k y a n d t e l e s c o p e .c o m

* MAY 2017

47
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Sky and Telescope - May 2017

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