To the reader:
The Skywatcher's Diary for December 2005 has been prepared by
Robert C. Victor, formerly Staff Astronomer (now retired). Credit to the author and to
Department of Physics and Astronomy at
Michigan State University, and mention of
Sky Calendar, would be
A sample issue of the Sky Calendar is available over the Internet. It
can be viewed via the World-Wide Web at
If you would like a printed sample of the December issue, please send a long,
self-addressed stamped envelope to:
December Sky Calendar
Michigan State University
East Lansing, MI 48824
Each month, the Department of Physics and Astronomy at Michigan State
University makes the Skywatcher's Diary available over the Internet. It can
be accessed at
Current and back-issues of the Skywatcher's Diary are available in our
Naked-eye planets and Moon in December
Venus and Mars are still in first and second place in order of brilliance among all
"stars" visible at dusk. Venus in early December attains its highest position at dusk and greatest brilliance for this
apparition (which began last spring), and sets nearly 3 hours after sunset.
Venus can even be spotted in daylight if you know where to look. Daytime
sightings of Venus are easiest just before sunset, when the planet is found to
the upper left of the Sun, by 43 degrees on Dec. 1, shrinking to 20 degrees by
Dec. 31. Even binoculars reveal Venus is a crescent now, growing in apparent
diameter but becoming thinner as the planet begins to swing between Earth and
Sun. On Dec. 1 the crescent Venus appears about one-third full; on the 31st,
only 6 percent full. After this month, you'll have to wait more than one and a
half years, until July 2007, for a repeat performance. That's because Venus in
its 225-day orbit overtakes the Earth about every 584 days, or just over 19
months. Mars is in E to ESE at
dusk, climbing high as month progresses. In December, Mars fades a full
magnitude as Earth leaves it behind. Of magnitude –0.6 at month's end,
Mars still ranks after only Venus in brilliance in the early evening sky (until
the "Dog Star" Sirius rises in ESE below Orion later in evening).
planets: Rising in evening, Saturn first
appears in ENE 4-1/2 hours after sunset on Dec. 1, backing to 2-1/4 hours after
on Dec. 31. Look 19 to 18 degrees below Pollux, the brighter and lower of the Gemini
Twins. For the next several months, whenever Saturn is high in the sky,
binoculars will show the Beehive star cluster in the same field.
bright planets at dawn: Jupiter is the
brightest morning "star," climbing slowly in SE to SSE at dawn in December.
Note the first-magnitude star Spica in Virgo 14 to 20 degrees to Jupiter's
upper right. Saturn is high in
WSW at dawn in early December and moves lower, into the west. Mercury brightens quickly the first week and is in fine
view nearly all month. Look low in ESE to SE in twilight, to the lower left of
two New Moons this month, on Dec. 1 and
30, and so a complete cycle of lunar phases, from young crescent to Full to old crescent,
may be observed in December. Moon
near planets: Venus on evening of Dec. 4,
Mars on evening of Dec. 11, Saturn on night of Dec. 18-19, Jupiter on mornings
of Dec. 26, and 27, Mercury on morning of Dec. 29, and Venus on evening of Jan.
Following is a day-by-day guide to
celestial happenings during December. For drawings of many of these events, and
an evening sky map, request a free sample copy of the Abrams Planetarium Sky
Calendar by sending a self-addressed,
stamped envelope to Sample Sky Calendar, Abrams
Planetarium, Michigan State University, East Lansing, MI 48823. Or you can
subscribe for $11 per year.
Skywatcher's Diary: December 2005
New Moon 10:01 a.m. EST. Using binoculars all month at
sunset, observe Venus' crescent phases.
Locate bright Jupiter in SE an hour before sunrise. During
Dec. 2-8, Mercury brightens considerably and stays 17 degrees lower left of
Jupiter as both climb higher daily. Mercury will reach its peak elevation
Shortly after sunset, the 2.3-day-old Moon will be easy to
see in SW, 12 degrees lower right of Venus. Be sure to look again on Sunday
See Venus in the daytime! The 3-day-old crescent Moon passes
due south, about one hour before sunset in south Florida, 1-1/2 hours before
sunset near lat. 40 degrees N, and 2 hours before sunset along the Northern
Tier of the U.S., from MN to WA. (Near Lansing, MI, the Moon passes due south,
20-21 degrees up, at 3:38 p.m. EST.) Venus should then be easy to find, about 3
degrees to Moon's upper right. Binoculars and telescopes show Venus as a
crescent, about 30 percent full. By an hour after sunset Venus and Moon are
sinking toward SW, and still appear within 4 degrees apart. This striking sight
– Venus near the crescent Moon at dusk – will occur only once more
during Venus' current evening appearance, on Jan. 1, but Venus will appear much
lower then, because it will pass nearly between Earth and Sun only 12 days
later, on Jan. 13.
Tonight an hour after sunset, locate the Moon well up in SSW
with Venus 16 degrees lower right.
For almost the rest of December, Mars lingers 9 degrees from
the 2nd-mag. star Hamal, or Alpha in the constellation Aries, the Ram. Tonight
at nightfall, find Mars high in ESE and Hamal to its upper left.
Tonight at sunset, you'll find the Moon in SSE nearly a
quarter-turn to the left, or east, of the setting Sun. Note the Moon's shape is
almost half full. The Moon passes First Quarter phase overnight, and by
Thursday evening will appear a little more than half full.
An hour before sunrise
these mornings, we get a preview of the stars we'll see in the evening sky next
spring. This December, we also get three bright planets: Saturn high in the
southwestern sky, Jupiter (now the brightest morning "star") in the southeast,
and Mercury rising in the east-southeast. The plane of our solar system is well
marked by the lineup of Saturn-Regulus-Spica-Jupiter-Mercury. Along that line,
as background to the solar system bodies, lie the zodiac constellations Taurus
(setting)-Gemini-Cancer-Leo-Virgo-Libra. Well north of the plane of the solar
system, the Big Dipper and Arcturus will also be in good view.
Venus reaches greatest brilliancy, at –4.6 on the
scale of magnitudes astronomers use to describe apparent brightness. On this
scale, a planet of mag. –4 is five magnitudes brighter or 100 times as
bright as a first-magnitude star of mag. +1. Venus stays at essentially the
same brilliance for two weeks before and after Dec. 9, over 200 times as bright
as the star Fomalhaut at mag. +1.2, in the south 40 degrees upper left of Venus
before nightfall tonight. (From Lansing, MI, Fomalhaut passes due south, 18
degrees up, at 6:21 p.m. EST.)
Tonight Mars ends retrograde, or backward motion against the
stars, 22 degrees west of the Pleiades star cluster. At nightfall look for Mars
16 degrees to the Moon's lower left, and for the Pleiades 22 degrees lower left
of Mars. Moving eastward, Mars will pass only 2 degrees south of the cluster
Feb. 16-18. Not until mid-Nov. 2007, a little over a month before Earth
overtakes it next time, will Mars again reverse direction against the stars.
Just before sunset today, here's an easy chance to try for
Mars in the daytime while the red planet is still quite bright, near mag.
–1. Find the Moon well up in east shortly before sunset, then, aiming
binoculars at the Moon, look in the same field about 3 degrees to Moon's lower
left for Mars. After sunset, Mars is easy to see even though it appears close
to the Moon. Around 8 p.m. PST, or around 12:30 a.m. EST as seen from Lansing,
MI, the Moon passes just over a Moon's width north of Mars.
On Monday morning, one hour before sunrise, Mercury reaches
its "greatest elongation," or maximum angular distance from the Sun on this
trip around, 21 degrees. Look for Mercury low in ESE, 20 degrees lower left of
the brightest morning planet, Jupiter in SE. This week and next are especially
favorable for viewing Mercury, which is lost in the Sun's glare most of the
At nightfall, about 1-1/2 hours after sunset, look for the
Moon well up in E, with Mars 11 degrees upper right and the Pleiades about 11
degrees lower left. By Tues. evening at this time, the Moon will have passed 2
or 3 degrees to the lower left of the Pleiades. Next year, on several
occasions, the Moon will occult or cover up part of this star cluster.
Tonight's peak of the Geminid meteor shower will be spoiled
by the light of the nearly Full Moon.
At nightfall, look for the star Aldebaran, follower of the
Pleiades and eye of Taurus the Bull, 11 degrees right of the Moon.
Tonight's northernmost Full Moon of the year rises 40
degrees north of east at 4:46 p.m. EST in the Lansing, MI area, or just before
sunset. Ten minutes later, if you have unobstructed views, it will be possible
to view the Sun and Moon simultaneously. As you face the rising Moon, note the
dark blue wedge of sky on the ENE horizon with pink border at its upper edge
– the Earth's shadow projected on our atmosphere! It's visible most clear
evenings (and mornings too, just before sunrise, in the opposite direction from
the rising Sun), regardless of the Moon's phase.
Two-and-a-half hours after sunset, look for Moon in ENE with
the heads of the Gemini Twins, Castor above Pollux, 10 to 12 degrees to Moon's
lower left. On Saturday morning one hour before sunrise, the Moon is in W to
WNW, below the Gemini Twins. Bright Jupiter is in Libra, well up in SE, and
Mercury is near the head of Scorpius, low in ESE 25 degrees to Jupiter's lower
left. Saturn is in Cancer in the western sky, 25 degrees upper left of Moon and
90 degrees from Jupiter.
Three hours after sunset, Moon is in ENE, with the Gemini
Twins Pollux and Castor 2 and 7 degrees to Moon's upper left. An hour before
sunrise on Sunday, the Moon is well up in west, with the Twins 5 to 10 degrees
to Moon's lower right, and Saturn 13 degrees to Moon's upper left.
Four hours after sunset, find the waning gibbous Moon low in
ENE, with Saturn 5 degrees lower right. On Monday one hour before sunrise, find
Moon high in west with Saturn 3 degrees lower left.
Four hours after sunset, find Moon rising in ENE with Saturn
9 degrees upper right. About 1-1/2 hours later, look for Regulus, heart of Leo,
11 degrees below the Moon. An hour before sunrise on Tuesday, Moon is high in
WSW, with Saturn 12 degrees lower right, and Regulus 8 degrees left.
Six hours after sunset, locate Moon low, a little north of
east, with Regulus 3 degrees upper right. An hour before sunrise on Wednesday,
find Moon high in SW, with Regulus 5 degrees lower right. Note the lineup of
Saturn (24 degrees to Moon's lower right)-Moon-Jupiter (in SE)-Mercury (low in
ESE). Using binoculars, watch for Antares rising 6 degrees to Mercury's lower
Winter begins today at 1:35 p.m. EST, when the Sun stands
directly over the Tropic of Capricorn, its southernmost excursion. Midway
between sunrise and sunset today, when the Sun passes due south, we have our
lowest midday Sun of the year. From Lansing, MI, midday occurs at 12:36 p.m.
EST, with the Sun just under 24 degrees above the horizon. An hour before
sunrise on Thursday, look for Mercury low in ESE to SE, 30 degrees lower left
Sky is dark and moonless at nightfall, allowing fine views
of the Pleiades star cluster 21 degrees lower left of Mars, and later in the
evening, the Great Nebula of Orion, visible in binoculars in the Hunter's
Sword. The Moon rises just north of east in the very late evening (or just
after midnight in Lansing, MI) as Orion stands high in the south, and by
sunrise on Friday the Moon is in SSW to SW, just over 90 degrees or one-quarter
circle west of the rising Sun. Last Quarter phase occurs several hours later.
Venus can still be spotted in daylight, 29 degrees upper
left of the setting Sun. Using binoculars, when the sky becomes dark, look for
the 3rd-mag. star Beta Capricorni five degrees upper right of Venus, and the
double star Alpha Cap 2.4 degrees upper right of Beta. Venus now begins
retrograde, and lingers 4 or 5 degrees below Beta through Jan. 2.
Three hours after sunset, find the Gemini Twins Pollux with
Castor 4-1/2 degrees above, in ENE. Look for the 3.5-mag. star Delta in Gemini
8 degrees right of Pollux. Tonight binoculars show the 6.5-mag. asteroid Vesta
very closely S of Delta. For the next few evenings, Vesta moves one-quarter of
a degree per day, toward the upper right, away from the star.
On Christmas morning, the Moon, one-third full, occults or
covers the first-magnitude star Spica before sunrise from eastern AK, western
Canada, and parts of western and north-central U.S., east of a line through AK,
WA, OR, NV, UT, AZ, NM, to Big Bend of TX. From eastern and southern U.S.,
event is after sunrise. From Lansing, MI the star is less than a degree from
the Moon's bright lower left edge on Sunday Dec. 25 as morning twilight begins
at 6:25 a.m. EST. Watch the Moon close in on the star as twilight brightens.
With binoculars or a telescope, you can follow the star until after sunrise as
the Moon closes in. From Lansing the star disappears (in daylight) at the
Moon's bright edge at 8:48 a.m. EST, and reappears at the Moon's invisible dark
edge just before 10:09 a.m. For times of Spica's disappearance and reappearance
for other cities, visit the web site of the International Occultation Timing
Association at http://www.lunar-occultations.com/iota
and follow the link to Bright Star Occultations for North America.
An hour after sunset, Venus is low in SW, while Mars is high
in ESE. An hour before sunrise on Monday, Saturn is well up in W, Jupiter is in
SE to SSE, 8 degrees to Moon's left, while Mercury is just rising in ESE to SE,
35 degrees to Jupiter's lower left.
The brightest evening "star" is Venus, sinking into WSW an
hour after sunset. The brightest morning "star" is Jupiter, 8 degrees above the
Moon an hour before sunrise on Tuesday.
Four hours after sunset, locate Saturn low in ENE to E, and
Mars high in SSW. Tonight Mars and Saturn are 90 degrees apart. (They'll pass
close to each other in the evening sky on June 17, 2006.) An hour before
sunrise on Wednesday, find the crescent Moon in SE with Antares 7 degrees lower
left. Watch for Mercury rising 12 degrees lower left of Antares.
Just before sunset, find Venus 24 degrees to Sun's upper
left. Binoculars show Venus as a crescent, 0.9 arcminute (less than 1/60 of a
degree) across and 8 percent illuminated. Forty-five minutes before sunrise on
Thursday, a thin crescent old Moon is very low in SE, with Antares 7 degrees to
its upper right, and Mercury 8 degrees left.
An hour after sunset, the six brightest objects visible are
Venus very low in SW to WSW, Mars high in ESE, Vega in WNW, Capella in NE to
ENE, Rigel very low in ESE, and Betelgeuse very low in E. The latter two stars mark one foot and
one shoulder of Orion. Midway between them lies a vertical row of three stars
marking the Hunter's belt. Robert Frost aptly described the scene in the
opening lines of his poem, the Star-Splitter:
You know Orion always comes up sideways.
The Moon is New, for the second time this month, at 10:12
p.m. EST. On Saturday 1-1/2 hours before sunrise, find bright Jupiter in SE to
SSE, and the 3rd-mag. star Alpha Librae two degrees to its lower left.
(Binoculars reveal this star to have a close 5th-magnitude companion.) On Jan.
13, Jupiter will pass only 3/4 of a degree north of Alpha.
This evening, Venus is only 20 degrees upper left of the
setting Sun. On what date will you last see Venus before it is lost in the
glare of the Sun? Venus will pass nearly between Earth and Sun on January 13,
and will emerge into the ESE morning sky a few days later.
Throwing a leg up over our fence of mountains. . .
Please send any comments, suggestions, or questions to
Thomas G. Ferguson: