Sky and Telescope - July 2018 - 47
as the planet's apparent motion slows
to a halt during the night of July 10-11.
Then the planet resumes direct motion,
creeping eastward against the background of the stars.
DUSK TO DAWN
Saturn was at opposition on June 27th
and so starts July visible from dusk
to dawn. Its magnitude fades from
+0.0 to +0.2, but the golden planet
continues to glow in the midst of the
Sagittarius Milky Way, slowly retrograding west to within a few degrees
of M8, the Lagoon Nebula, and M20,
the Trifid Nebula. The globe of Saturn
has an apparent equatorial diameter
of about 18″ (similar to that of Venus
a little after mid-month). The rings of
Saturn gloriously remain open to 26°,
nearly their maximum tilt. Saturn is
highest around midnight or late evening this month.
Mars begins the month rising about
two hours after sunset and already glaring at magnitude -2.2, ever so slightly
dimmer than Jupiter. But the campﬁrecolored planet reaches opposition on
the night of July 26-27, rising less than
half an hour after sunset and peaking at -2.8 for the ﬁnal week of July
and opening nights of August. Mars
comes closest to Earth on the night
ORBITS OF THE PLANETS
The curved arrows show each planet's movement during July. The outer planets don't change
position enough in a month to notice at this scale.
of July 30-31 and attains a diameter
of 24.3″. Mars is more than 24″ wide
from July 24th through August 8th and
wider than 18.6″ (its maximum 2016
diameter) from June 20th to September
13th (virtually all summer).
Mars follows a little bit more than
30° behind ringed Saturn throughout
July, retrograding just above faint Psi
(ψ) Capricorni around mid-month.
For detailed information on observing Mars (and its two moons), see the
article on page 22 of this issue of the
magazine and skyandtelescope.com/
Dusk, July 23 -25
Looking Southwest, halfway up
C a t 's
1 hour after sunset
Dusk, July 19 - 20
1 hour after sunset
S A G I T TA R I U S
Neptune is almost at its highest in the
south during July dawns, Uranus a few
hours behind it in the sky (see https://
is.gd/urnep for ﬁnder charts).
EARTH AND MOON
Earth reaches aphelion, its farthest
from the Sun in space, at 1 p.m. EDT on
July 6th, at 1.02 a.u. (152,095,566 km).
A thin waning crescent Moon is
closer than 1° to Aldebaran at dawn
on July 10th. An even thinner waxing crescent shines less than 2° above
Mercury about 45 minutes after sunset
on July 14th. It's 2° right of Venus the
next night. The waxing gibbous Moon is
some 3½° above Jupiter at nightfall on
July 20th and 2° upper right of Saturn
on July 24th.
The full Moon is totally eclipsed in
Europe, Africa, and Asia on July 27-28.
Look for Mars lower left of the action
(see page 50 for details).
¢ Contributing Editor FRED SCHAAF
welcomes your comments at fschaaf@
t These scenes are drawn for near the middle
of North America (latitude 40° north, longitude
90° west); European observers should move
each Moon symbol a quarter of the way toward
the one for the previous date. In the Far East,
move the Moon halfway. The blue 10° scale bar
is about the width of your fist at arm's length.
For clarity, the Moon is shown three times its
actual apparent size.
s k y a n d t e l e s c o p e . c o m * J U LY 2 0 1 8