Sky & Telescope - September 2016 - 47

Fred Schaaf

To ﬁnd out what's visible in the sky from your location, go to skypub.com/almanac.

O R B IT S O F THE P L ANE T S

December
solstice

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

Mercury

March
equinox

sunlit. Mars recedes to 1 astronomical
unit behind the faster Earth on September
19th, its disk dwindling from an apparent
diameter of 10½″ to almost 9″ during September. Given its low altitude, that's small
enough to make spotting even large surface features hit or miss. Saturn's 16″-wide
globe and 37″-span rings oﬀer a thrilling
sight as usual, especially considering that
the rings remain tilted 26° from edge-on,
just short of their maximum openness
(which they'll reach next year).
As September starts, both Mars and
Saturn set not too long before midnight
daylight-saving time. By month's end
Mars remains up until about 11 p.m., but
Saturn sets well before 10 p.m.

NIGHT
Neptune reaches opposition on September 2nd, at magnitude +7.8 in Aquarius.
Although it rises around sunset, the

Dawn, Sept 27-29
45 minutes before sunrise

a
Regulus

Moon
Sept 28

Mercury
Denebola
Moon
Sept 29

Looking East

Moon
Sept 27

Sun

Earth

Venus

Sept.
equinox

Mars

June solstice

Uranus

Jupiter
Saturn

Neptune

Pluto

best time to see its tiny 2.3″ dot in the
telescope is in the middle of the night.
Finder charts for Neptune and for 6thmagnitude Uranus, in Pisces (about two
hours behind Neptune) can be found at
skyandtelescope.com/urnep.
14th-magnitude Pluto remains in the
Teaspoon of Sagittarius. With a 12-inch
scope you can still seek it just after nightfall, using the ﬁnder charts in the July
issue, page 48.
Far easier are two asteroids close
together. On the American night of
September 8-9, 1 Ceres (magnitude +8.2)
and 18 Melpomene (magnitude +8.7) are
just 2/3° apart near the head of Cetus. See
page 51 for details.

DAWN
Mercury, after dropping very low in
the dusk in late August, passes through
superior conjunction on September
12th. By the last week of September it
emerges into its best morning apparition
of the year for observers at mid-northern
latitudes. Mercury brightens by almost
three magnitudes in nine days: from
magnitude +2.5 - too faint to see low in
bright twilight - on September 19th to

-0.4 on the 28th, when it reaches greatest
elongation (18° west of the Sun). On that
morning Mercury rises about 1½ hours
before sunrise, just as dawn is beginning,
and it stands about 9° high due east 45
minutes before sunrise.

SUN AND MOON
The Sun experiences an annular solar
eclipse as seen from parts of Africa on
September 1st; see details at http://is.gd/
Sep2016annulareclipse. The Sun crosses
the September equinox at 10:21 a.m. Eastern daylight-saving time on September
22nd, marking the start of autumn in the
Northern Hemisphere and spring in the
Southern Hemisphere.
The Moon undergoes a deep penumbral eclipse visible from much of the
Eastern Hemisphere on September 16th.
Try for the ultra-thin lunar crescent as it
slices very near Jupiter soon after sunset
on September 2nd. A thicker Moon is
well upper left of Venus on the 3rd, and
above faint Spica on the 4th. The Moon is
above Saturn on September 8th and far
upper left of Mars the next night. A waning lunar crescent is just below Mercury
at dawn on September 29th. ✦

Sk yandTelescope.com September 2016

47
http://www.skypub.com/almanac http://www.skyandtelescope.com/urnep http://www.is.gd/Sep2016annualareclipse http://www.is.gd/Sep2016annualareclipse http://www.SkyandTelescope.com
Sky & Telescope - September 2016

Table of Contents for the Digital Edition of Sky & Telescope - September 2016
