48 September 2014 sky & telescopeOBSERVING
Sun, Moon && PlanetsMars Meets Its Rival
The Red Planet has a fi ne conjunction with Antares this month.
Mars and Saturn shine low in the south-
west early on September evenings. Mars
remains at almost the same altitude all
month, but Saturn descends a little lower
into the sunset each evening. Then late
in the month Mars has a fi ne conjunc-
tion with similarly colored Antares. And
Mercury may be visible at dusk through
telescopes and binoculars.
The other two bright planets shine in
the east at dawn: Jupiter high and climb-
ing, Venus very low and sinking.DUSK
Mercury has its worst evening apparition
of 2014 for mid-northern latitudes — vis-
ible only with optical aid shortly after
sunset. It’s at greatest elongation (26°
east of the Sun) on September 21st, but it
appears very low in the west for northern
observers due to the shallow angle that the
ecliptic makes with the horizon at dusk at
this time of year.
Conversely, this is Mercury’s best
evening apparition of the year from the
Southern Hemisphere, where the eclipticis as close to vertical as it ever can be as
the Sun’s glow fades.
For an interesting observing challenge,
go to a spot with a completely unob-
structed western horizon before sunset on
September 20th. Note the spot where the
Sun disappears, and then start scanning
with a telescope or binoculars 25° left of
that point and 5° to 10° above the horizon
for zero-magnitude Mercury. Then look
carefully for 1.0-magnitude Spica just 0.6°
to Mercury’s right.EARLY EVENING
Saturn begins September less than 6° to
the right of identically bright Mars, but
the gap between them widens rapidly as
Mars races eastward relative to the back-
ground stars. Saturn is moving eastward
too, though much more slowly, so its
separation from Alpha Librae (Zubenelge-
nubi) increases slightly. The ringed planet
maintains its magnitude of +0.6, and its
rings now open to more than 23° from
edge-on. But Saturn stands only about 20°
high in the southwest an hour after sunsetat the start of the month and about 10°
high an hour after sunset at month’s end.
The interval between sunset and Saturn-
set decreases from about 3 to 2 hours
during September.
Mars dims a trace from magnitude
+0.6 to +0.8 in September, and its disk
shrinks from 6.8′′ to 6.1′′ across — too
small to show signifi cant detail through
most telescopes. However, Mars does
make an interesting trek out of Libra,
through the “fence” of stars marking the
head of Scorpius, and ends the month
just a few degrees from slightly fainter
Antares.
This month, Mars’s swift movement
eastward relative to the stars almost keeps
pace with the Sun’s. So Mars sets just
about 3 hours after sunset all month.
Mars appears halfway between Saturn
and Antares on September 12th. On the
17th Mars glides just ½° north of the
fascinating 2nd-magnitude variable star
Delta Scorpii (Dschubba). The other stars
in Scorpius’s head (including the bright
double Beta Scorpii and the naked-eye
Omega pair) also make for a pretty scene
with Mars around this date.
But the most interesting and attrac-
tive event in Mars’s September journey is
its passage north of Antares, the “rival of
Mars” in color. Mars is 1½° south of the
ecliptic now, so it passes just 3.1° north of
slightly dimmer Antares on September
27th and 28th. Compare the hues of the
planet and star with naked eye and bin-
oculars. Which seems redder — or at least
a deeper orange-gold?
Next month Mars will have a very close
encounter in space with Comet C/2013 A1
Siding Spring.
Dim Pluto is highest (though not very
high) in Sagittarius as darkness falls, and
it sets in the middle of the night. See page
50 of the June issue if you wish to seek it.Dusk, Around Sept 5
1 hour after sunsetAntares
MarsSaturnLooking Southwest`Sco`Lib_LibbSco10 °Dawn, Sept 5
30 minutes before sunriseRegulusVenusJupiterLooking EastLess than
1° apart!SMP layout.indd 48 6/23/14 12:18 PM