Sky & Telescope - July 2019 - 46

JULY 2019 OBSERVING
Sun, Moon & Planets by Fred Schaaf
To find out what's
visible in the sky
from your location,
go to skypub.com/
almanac.

Gas Giant Gaze
Three bright planets leave us for a while, but the two that remain
accompany us throughout the night.

T

his is a month when we lose sight
of three of the ﬁve classic bright
planets - Mercury and Mars in the
Sun's afterglow and Venus in the solar
glare just before sunrise. Our compensation is that the other two bright
planets, Jupiter and Saturn, are visible
most of the night, at or near their
brightest and biggest.
There are also two eclipses viewable
in parts of our world (though not North
America) during July. One is a total
solar eclipse, the other a partial lunar.

DUSK ONLY
Mercury, low in the west-northwest at
dusk on July 1st, has dimmed to magnitude 1.1 and is lost from view as it fades
rapidly in the following days. The little
world reaches inferior conjunction with
the Sun on July 21st - the last such
event before its rare transit across the
Sun's face on November 11th.
Mars shines at its (almost) dimmest
magnitude of 1.9 all this month as it
descends ever so slowly deeper into the
Sun's bright afterglow. In the opening days of July it lies about 4° right of
Mercury, and on July 3rd is about 3°
upper left of a very thin crescent Moon
- all very low in the west-northwest.
It will only be visible at more southerly
latitudes in North America.
Note that The Astronomical Almanac estimates that Mars and Mercury
at dusk and Venus at dawn should all
be lost from view during, or by about
the end of, the second week of July.
Mercury will then be out of visibility
for a few weeks until it reappears in the
morning sky at the end of July, Venus
for two months, and Mars for about
three months.
46

J U LY 2 0 1 9 * S K Y & T E L E S C O P E

ALMOST ALL NIGHT
Jupiter reached opposition back on
June 10th. But it begins the month
of July still as brilliant, at magnitude
-2.6, and still almost as big, at 45.5″
wide. By the end of July the kingly
world has faded a bit - to -2.4 - and
shrunk a little - to 43″ - but remains
a rich and rewarding sight in telescopes. (See pages 50-51 for the best
times to observe the Galilean moons
and the Great Red Spot.)
For viewers around latitude 40°
north, Jupiter sets as early as about
2 a.m. daylight-saving time at month's
end. The time Jupiter culminates (when
it's at its highest) backs up from a little
before 11:30 p.m. in early July to a little
after 9 p.m. local time, in evening twilight, at month's end.
Jupiter continues to retrograde
(move westward with respect to the
background stars) in July, a little less
than 7° separating it from Antares by
month's end.
Saturn comes to opposition on
July 9th so is visible virtually all night
throughout the month. Saturn shines
at magnitude +0.1 left of the Teapot

asterism of Sagittarius. A closer look
ﬁnds the ringed planet hanging like a
gleaming droplet just spilled from the
little Teaspoon asterism.
Saturn's oblate globe reaches an
equatorial diameter of 18″. The rings
span almost 42″ in your telescope and
are tilted more than 24° from edgewise. But viewers around latitude 40°
north will see Saturn less than 1/3 of the
way up the sky even when at its highest in the south. That time for Saturn
occurs a little after 1:30 a.m. daylightsaving time on July 1st but around
11:30 p.m. on July 31st.
Pluto reaches opposition on July
14th - the exact anniversary of the day
the New Horizons spacecraft passed
closest to it in 2015. Pluto isn't far from
Saturn in eastern Sagittarius but you'll

Dusk, July 5 -6

Denebola

1 hour after sunset

LEO
Moon
July 6

Dusk, July 3-4

Sickle

30 minutes after sunset
10°

Moon
July 4

Mercury

Mars

Pollux

Regulus

Moon
July 5

Castor

Moon
July 3

Looking West-Northwest

Looking West
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Sky & Telescope - July 2019

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