Sky and Telescope - January 2017 - 46

JANUARY 2017 OBSERVING
Sun, Moon & Planets by Fred Schaaf

The Evening Star Reigns Supreme
Venus lights the southwest in twilight, while Mars and Neptune rendezvous nearby.

T

h e year 2017 wastes no time in getting off to a great start. New Year's
Eve brings the closest observable pairing
of any two planets in almost 30 years.
Mars and Neptune reach almost a minimum conjuction for observers in the
Paciﬁc, though they won't be quite so
close for North America. Venus passes
through greatest elongation this month,
gaining altitude for observers at midnorthern latitudes as it pulls closer to
much dimmer Mars. This planetary duo
is well up in the southwest at nightfall
and sets around mid-evening.
Jupiter rises around midnight and
shines highest in the south by dawn.
Saturn glows low in the southeast dur-

Moon
Jan 3

Jan 1- 3
Around 6 pm
Mars

Moon
Jan 2

Venus

ing early dawn, and to its lower left,
little Mercury makes a morning appearance after the ﬁrst week of the month.

DUSK & EARLY EVENING
Venus reaches a greatest elongation of
47° east of the Sun on January 12th. The
resplendent planet sets about 4 hours
after the Sun all month for observers
around latitude 40° north.
As Venus moves north along the
ecliptic, it gains height: its altitude at
sunset increases from 33° to 40° during
January. Its brightness improves from
magnitude -4.4 to a near-maximum
-4.7. In a telescope Venus's apparent
diameter grows from 21″ to 30″ while its

Dawn, Jan 18-20
1 hour before sunrise

Arcturus

Moon
Jan 1

b Cap
Fomalhaut

a Vir
Moon
Jan 18

Moon
Jan 19
Moon
Jan 20

10°

Looking Southwest

46

J A N U A R Y 2 0 1 7 * SK Y & TELESCOPE

Jupiter
Spica

Looking South, high in the sky

phase wanes from 58% to 40% sunlit.
On which night after greatest elongation
does it appear half-lit in your telescope? Look each evening, then ﬁnd the
midpoint between the date when it last
looked a trace gibbous and the date when
its terminator ﬁrst appears indented.
Mars is easy to ﬁnd this month, not
far upper left of Venus. On the night
of December 31-January 1 in North
America, Mars experiences an ultraclose conjunction with 8th-magnitude
Neptune. The two worlds appear just
68″ apart at 6:53 UT January 1st as
viewed from Hawai'i and the Paciﬁc.
The pairing is already tight a few hours
earlier when visible from the continental United States: they're 0.2° apart as
seen just after dark from the East Coast,
and 0.1° from the West Coast, with
Neptune more or less above Mars. The
globe of Mars at this conjunction is 5.7″
wide while Neptune's is 2.2″. Neptune
is almost 20 times farther and 6 magnitudes fainter than Mars.
The brightness of Mars diminishes
from magnitude +0.9 to +1.1 during January as blazing Venus chases it
across Aquarius. The two planets end
the month just left of the Circlet of
Pisces asterism. By January 31st the gap
between Venus and Mars has shrunk
down to 5½°, and the two planets form
a compact triangle with the month's
second young crescent Moon.
Venus, following behind Mars, passes
0.4° from Neptune on January 12th,
the date of Venus's greatest elongation.
Uranus is still high in the westsouthwest after nightfall. Finder charts
for Uranus and Neptune are on page 50
of the October 2016 issue.
Sky and Telescope - January 2017

Table of Contents for the Digital Edition of Sky and Telescope - January 2017
