Sky & Telescope - July 2023 - 47

+30°
+40°
6h
4h
Castor
July
13
Procyon
0°
+10°
GEMINI
TAURUS
Betelgeuse
ORION
-10°
-20°
-30°
-40°
Rigel
Sirius
ERIDANUS
CANIS
MAJOR
10 am
8 am
LOCAL TIME OF TRANSIT
6 am
4 am
CAPRICORNUS
28
Fomalhaut
2 am
SAGITTARIUS
Midnight
July
2 - 3
10 pm
Antares
SCORPIUS
8 pm
6 pm
4 pm
2 pm
CETUS
7
PEGASUS
CYGNUS
ARIES
Uranus
Jupiter
10
AQUILA
PISCES
Neptune
Saturn
AQUARIUS
LIBRA
25
Spica
HYDRA
CORVUS
OPHIUCHUS
VIRGO
July 22
Mars
Regulus
EQUATOR
-10°
-20°
-30°
-40°
The Sun and planets are positioned for mid-July; the colored arrows show the motion of each during the month. The Moon is plotted for evening
dates in the Americas when it's waxing (right side illuminated) or full, and for morning dates when it's waning (left side illuminated). " Local time of transit "
tells when (in Local Mean Time) objects cross the meridian - that is, when they appear due south and at their highest - at mid-month. Transits
occur an hour later on the 1st and an hour earlier at month's end.
than 2½° between the cluster and the
crescent, this is both a fine naked-eye
conjunction and a tempting binocular
treat. The boost in magnification and
light-gathering that binos provide will
make the individual cluster stars easier
to see and enhance the visibility of
earthshine on the Moon's " unlit " face.
The very best meetings between the
Moon and the Pleiades are those that
occur late in the morning in summer
or early in the evening in spring. It's
during those two windows that the
Moon is a slender crescent when it
encounters the cluster. At other times
of the year light from the increasingly
illuminated Moon can overwhelm the
cluster's stars, making for a much less
satisfying sight.
Dusk, July 23 - 24
9 pm
Spica
Moon
July 24
VIRGO
WEDNESDAY, JULY 19
Activity low in the west-northwestern
sky at dusk has been eye-catching all
month but reaches a kind of climax
tonight when a young, crescent Moon
adds its luster to a jewel box of wonders.
First, we have the aforementioned
lunar crescent (still beautifully adorned
with earthshine). Next, below and left
of the Moon, is the can't-miss-it bright
planet, Venus. Right of Venus and
the Moon there's Mercury, shining at
magnitude -0.4 as it approaches the
midpoint of its current evening apparition.
About 4° above Venus is Regulus,
in Leo, while Mars lurks less than 6°
above left of Regulus. Taken together,
the five objects are an impressive collection
of celestial gems.
Although I've highlighted the
Moon
July 23
CORVUS
evening of the 19th here, the show
remains captivating for several additional
nights. On the 20th, the Moon
has shifted eastward and makes an
attractive quartet with Mars, Regulus,
and Venus. And though the Moon has
moved on by the 22nd, keep watching
the gap between the solar system's two
innermost planets shrink as Mercury
ascends and Venus descends. By the end
of the month the reigning Evening Star
will surrender its crown and slip into
the Sun's glare. It'll surface again next
month, however, as the Morning Star.
Looking Southwest
MONDAY, JULY 24
This evening the Moon has its closest
stellar encounter of the month when it
approaches Alpha (α) Virginis, better
known as Spica. How close? That
depends on where you are. From the
East Coast 2° will separate the waxing
crescent and the 1st-magnitude star as
they sink toward the west-southwestern
horizon a little before midnight. However,
observers on the West Coast get
a slightly better show with the Moon
sitting just 1½° from Spica. Because the
star is neatly positioned just south of
the ecliptic, it gets monthly visits from
the Moon. The two meet up again on
August 20th, and that's about it for
evening pairings this year as Spica is
overtaken by twilight. Their rendezvous
resumes again at dawn in November.
FRIDAY, JULY 28
July wraps up with a tight dusk pairing
that includes Regulus and Mercury.
If you kept watching the dusk action
from the 19th onwards, this conjunction
won't come as a surprise - Mercury
has been edging closer and closer
to the star each night and tonight
they're a scant 10′ (1
/6°) apart. That's
close! However, there's an important
caveat to note. Mercury shines brightly
at magnitude -0.1 and Regulus at 1st
magnitude, but they're very low in the
west-southwest - just 6° above the
horizon 30 minutes after sunset. You'll
need an unobstructed view and (probably)
binoculars, too, to claim both
parts of this treat.
¢ Consulting Editor GARY SERONIK
never tires of watching the planets mix
and match at dusk.
sk yand tele scope .o r g * JULY 2023
47
Venus
+10°
0°
HERCULES
Arcturus
LEO
2h
0h
22h
20h
18h
Vega
16h
BOÖTES
14h
12h
RIGHT ASCENSION
10h
+30°
+40°
Mercury
DECLINATION
E
C
L
I
P
T
I
C

http://skyandtelescope.org

Sky & Telescope - July 2023

Table of Contents for the Digital Edition of Sky & Telescope - July 2023