Sky and Telescope - September 2018 - 47

upper left of M8 (the Lagoon Nebula)
and east of M20 (the Trifid Nebula),
and slowly begins to move eastward in
northern Sagittarius. During the month,
the gap between Saturn and Jupiter
closes from about 45° to 41°. On the
other side - eastward - Mars increases
its separation from Saturn from 27° to
33° during September. Saturn's rings
look even more three-dimensional than
usual this month with Saturn passing
through eastern quadrature (90° east of
the Sun) on September 25th. Saturn sets
a little after 1 a.m. local time on September 1st and a little after 11 p.m. on
September 30th.
Mars begins the month at a bracing
magnitude -2.1, still a bit brighter than
Jupiter. The imposing orange-yellow
beacon loses half of its brightness during
September, however, fading to magnitude -1.3. Its apparent diameter also
dwindles from 21″ to 16″ this month
- but even this is wider than Mars has
been in any of the past 13 years, bar one.
Furthermore, Mars reaches its highest
in the south conveniently early in the
night this month, passing the meridian
around 10:20 p.m. on September 1st and
a bit before 9 p.m. on September 30th.
In space, Mars reaches perihelion,
1.38 a.u. from the Sun, on September
16th. In the heavens, Mars is trekking
back from Sagittarius into Capricornus.

December
solstice

Uranus

Mercury
Jupiter

Mars
June
solstice

ORBITS OF THE PLANETS
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.

The Red Planet sets not long before 3
a.m. as September begins and a little
after 1:30 a.m. as the month ends.

ALL NIGHT
Neptune reaches opposition, visible all
night in Aquarius, on September 7th.
It shines at magnitude 7.8 and is 2.4″
wide in telescopes. Uranus glows in
southwestern Aries this month, two
magnitudes brighter than Neptune and
appearing considerably larger at 3.7″.
Neptune transits the meridian roughly
around midnight, Uranus about three
hours later. Finder charts for these two
planets are on pages 48-49.

α

Sept 28-30

β

Around 11 pm
Moon
Sept 19

Pleiades
Moon
Sept 28

Mars

CAPRICORNUS

TA U R U S
Moon
Sept 29

ζ

Looking South-Southeast

Sept.
equinox

Venus

Dusk, Sept 19-21

Moon
Sept 20

Earth
Sun

Neptune

Saturn

1 hour after sunset

Moon
Sept 21

March
equinox

Aldebaran

Moon
Sept 30

Looking East-Northeast

DAWN
Mercury appears low in the east-northeast 30 to 45 minutes before sunrise in
the first week of September. On September 5th and 6th, 1st-magnitude Regulus
may be glimpsed with optical aid a bit
more than 1° from Mercury, which
shines at magnitude -1. Mercury is lost
to view around September 11th and
reaches superior conjunction with the
Sun on September 20th.

SUN AND MOON
The Sun passes through the September
equinox at 9:54 p.m. EDT on September
22nd, marking the start of autumn in
the Northern Hemisphere and spring in
the Southern Hemisphere.
The Moon is a thin waning crescent
1¾° above Regulus (use binoculars)
at dawn on September 8th. The waxing lunar crescent is 9° upper right of
Venus at dusk on September 12th, but
only some 4° upper right of Jupiter
the next night. On September 17th a
slightly gibbous Moon is 4° left of
Saturn. A fatter Moon is almost 4½°
above Mars on the evening of September 19th. On the night of September
29-30, the waning gibbous Moon
passes less than 1° from Aldebaran for
North America. 
¢ Contributing Editor FRED SCHAAF
teaches astronomy at Rowan University
and Rowan College in Gloucester County,
both in southern New Jersey.
sk yandtelescope.com * S E P TE M B E R 2 018

47


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Table of Contents for the Digital Edition of Sky and Telescope - September 2018

Contents
Sky and Telescope - September 2018 - Cover1
Sky and Telescope - September 2018 - Cover2
Sky and Telescope - September 2018 - 1
Sky and Telescope - September 2018 - Contents
Sky and Telescope - September 2018 - 3
Sky and Telescope - September 2018 - 4
Sky and Telescope - September 2018 - 5
Sky and Telescope - September 2018 - 6
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