Sky & Telescope - December 2018 - 47

PRE-DAWN TO DAWN
Venus veritably vaulted up out of the
dawn during November, its sunrise
altitude increasing from about 5° to
32°. But in December the brilliant
planet gets only a little higher, reaching
its peak sunrise altitude of 33° on the
13th for observers at latitude 40° north.
Venus is even a little lower on December 31st than it was on December 1st.
The planet dims a bit from its maximum brightness of -4.9, ending the
month and year at -4.6. During December the angular diameter of Venus
decreases from 41″ to 26″, and its phase
increases from 25% to 46% illuminated.
Venus will reach greatest elongation
from the Sun on January 6, 2019.
Mercury was at inferior conjunction
with the Sun on November 27th, but
in December it leaps up into an excellent morning apparition. Too dim to see
at ﬁrst, Mercury kindles to magnitude
+0.5 by December 6th and +0.0 by the
8th. By December 15th, the ﬂeet world
is already at a greatest elongation of
21° from the Sun and rises almost 1¾
hours before the Sun (it also appears
more than 60% lit by then). Mercury's
q These scenes are drawn for near the middle
of North America (latitude 40° north, longitude
90° west); European observers should move
each Moon symbol a quarter of the way toward
the one for the previous date.

Dec 24-26

December
solstice

Earth
Mars
Uranus

March
equinox

Jupiter

Moon
Dec 24

Saturn

June
solstice

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

magnitude from December 12th to the
end of the month hovers around -0.4
or -0.5. But what's really exciting is its
close conjunction this month with an
even brighter planet, Jupiter.
Jupiter was at conjunction with the
Sun on November 26th and trails Mercury up into the dawn sky in December. Jupiter starts rising about an hour
before the Sun around December 12th,
with its -1.7-magnitude point of light
more than three magnitudes fainter
than mighty Venus. Jupiter was in Libra
before it was lost in the solar glare,
but in early December the giant planet
comes back out in Scorpius. At mid-

1 hour before sunrise

VIRGO

Moon
Dec 25

Moon
Dec 30
Regulus

Moon
Dec 26

Looking East

Sept.
equinox

Sun

Moon
Dec 29

Sickle
of
LEO

Mercury

Neptune

Dawn, Dec 29 -31

Around 10 pm

Venus

Moon
Dec 31

month Jupiter marches into Ophiuchus
and on December 20th passes 5° upper
left of the star Antares. Very low in the
southeast on the morning of December 21st, the biggest planet in the solar
system, Jupiter, is less than 1° from
the smallest planet, Mercury. Jupiter
appears 31″ across, Mercury 6″; Jupiter
is fully lit, Mercury ¾ lit. Note also the
much greater surface brightness of Mercury compared to Jupiter. In the ﬁnal
days of the year, Mercury continues to
appear lower and Jupiter higher.

SUN AND MOON
The Sun reaches the winter solstice
at 5:23 p.m. EST on December 21st,
ushering in winter in the Northern
Hemisphere and summer in the Southern Hemisphere.
The Moon is a waning crescent
forming a triangle with Venus and Spica
in the southeast at dawn on December
3rd. The waxing lunar crescent is about
4° lower right of Saturn at dusk on
December 8th. The ﬁrst-quarter Moon
is 4° below Mars on the evening of
December 14th. The Moon is waning
gibbous as it glides past Regulus between
December 25 and 26. The waxing crescent Moon is almost 7° above or upper
left of Spica at dawn on December 30th.

Spica

Looking South, high in the sky

¢ FRED SCHAAF is the author of The
Starry Room, published 30 years ago by
John Wiley & Sons and republished 16
years ago by Dover Publications.
sk yandtelescope.com * DECE MBE R 2 018

http://www.skyandtelescope.com

Sky & Telescope - December 2018

Table of Contents for the Digital Edition of Sky & Telescope - December 2018