Sky and Telescope - January 2018 - 47

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

December
solstice

Earth

On the morning of January 6th,
Jupiter is resplendent with Mars immediately to the right and the 2.6-magnitude wide double star Alpha (α) Librae
(Zubenelgenubi) some 2° to the planets'
upper right. Mars-colored Antares ﬂickers marginally into view early during
twilight in the southeast, more than 20°
to the lower left of the Jupiter and Mars
pair. As the month progresses the two
planets move away from Alpha Librae,
and Mars retreats from Jupiter while
advancing upon climbing Antares. Mars
passes north of Antares February 6th-
10th, and in July it will reach its best
opposition since 2003, shining at magnitude -2.8 and looming about 5 times
wider than at present in telescopes.
By the end of January, Jupiter rises
as early as 1:30 a.m. local time, Mars
at about 2:30 a.m., and both reach the
meridian in morning twilight.

DAW N
Mercury and Saturn form the second planetary pair in the ﬁrst half of
January, but much lower on the eastern
horizon. Mercury shines at magnitude
-0.3 as it reaches greatest elongation of
23° west from the Sun on New Year's
Day, and we'll be able to witness this
ﬁne apparition for a few more weeks
before the planet appears too low in the

Uranus

Mercury
Saturn

Venus

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

morning twilight. In contrast, magnitude-0.5 Saturn remains elusive during
the year's ﬁrst week but climbs progressively higher throughout the month.
On January 13th, at their closest,
Mercury and Saturn shine only 0.6°
apart. Mercury's gibbous globe is then
little more than 5″ across, not much
more than 1/3 the apparent diameter of
Saturn's globe, but it will exhibit much
greater surface brightness. Don't expect a
very sharp view of either planet, however,
for the two are still low in the southeast
even 30 minutes before sunrise. In fact, it
may be a challenge spotting Saturn with
the naked eye at any point that morning.
The situation will be quite different by
month's end when Saturn rises well over
2 hours before the Sun.

Jan 26 -27
Around 8 pm

TA U R U S
Pleiades
Moon
Jan 27

Saturn
Aldebaran

Moon
Jan 26

Mercury

Looking Southeast

Mars

ORBITS OF THE PLANETS

30 minutes before sunrise

Antares

Neptune

Sun

June
solstice

Dawn, Jan 13

Moon
Jan 13

Sept.
equinox

March
equinox

Jupiter

Looking South, high in the sky

E A R TH A N D M O O N
Earth reaches perihelion, its closest
approach to the Sun in its orbital path
through space, at 5:35 UT on January
3rd, when it is 98.3% of its average
distance from the Sun.
The Moon is full (for the ﬁrst time
this month) on the North American evening of January 1st - and
will appear slightly larger than usual
because it will be only about 4 hours
past perigee (when it's at its nearest
point in its orbit around the Earth). The
Moon then brushes past Regulus in Leo
on the left in the middle of the night
of January 4-5 (an occultation will be
visible throughout parts of northern
Canada and Alaska).
The waning crescent Moon forms a
beautifully compact triangle with the
gas giant Jupiter and rocky Mars before
dawn on January 11th. Very low in the
southeast, a much thinner lunar sliver
is just over 6° above Saturn on January 14th and some 4° left of Mercury
on January 15th. On January 31st the
Moon is full for a second time in the
calendar month for observers in North
America, and all but the eastern part of
the continent can witness that Moon
totally eclipsed (see p. 48 for more
details of this event).
¢ FRED SCHAAF founded "Dark Skies
for Comet Halley" and wrote the bill proposing the New Jersey Light Pollution
Study Commission, both in the 1980s.
sk yandtelescope.com * JA N UA RY 2 018

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Sky and Telescope - January 2018

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