Sky and Telescope - January 2016 - S7

Skygazer's
Almanac 40°N

FOR LATITUDES
NEAR 40° NORTH

What's in the
sky tonight?
When does the Sun set, and when does
twilight end? Which planets are visible?
What time does the Moon rise?
Welcome to the Skygazer's Almanac
2016 - a handy chart that answers
these and many other questions for
every night of the year. It is plotted for
skywatchers near latitude 40° north - in
the United States, Mediterranean countries, Japan, and much of China.
For any date, the chart tells the times
when astronomical events occur during
the night. Dates on the chart run vertically from top to bottom. The time of
night runs horizontally, from sunset at
left to sunrise at right. Find the date you
want on the left side of the chart, and
read across toward the right to ﬁnd the
times of events. Times are labeled along
the chart's top and bottom.
In exploring the chart you'll ﬁnd that
its night-to-night patterns oﬀer many
insights into the rhythms of the heavens.

The Events of a Single Night
To learn how to use the chart, consider
some of the events of one night. We'll
pick January 17, 2016.
First ﬁnd "January" and "17" at the
left edge. This is one of the dates for
which a string of ﬁne dots crosses the
chart horizontally. Each horizontal dotted line represents the night from a Sunday evening to Monday morning. The
individual dots are ﬁve minutes apart.
Every half hour (six dots), there is
a vertical dotted line to aid in reading
the hours of night at the chart's top or
bottom. On the vertical lines, one dot is
equal to one day.
A sweep of the eye shows that the line
for the night of January 17-18 crosses
SGA16R

2016

many slanting event lines. Each event line
tells when something happens.
The dotted line for January 17-18
begins at the heavy black curve at left,
which represents the time of sunset.
Reading up to the top of the chart, we
ﬁnd that sunset on January 17th occurs
at 5:01 p.m. Local Mean Time. (All times
on the chart are Local Mean Time, which
can diﬀer from your standard clock time.
More on this later.)
Moving to the right, we see that
the bright star Sirius rises at 5:54 p.m.
Evening twilight ends at 6:36, marking
the time when the Sun is 18° below the
horizon and the sky is fully dark.
At 7:05 p.m. Polaris, the North Star,
is at upper culmination. This is when
Polaris stands directly above the north
celestial pole (by 40′ this year), a good
time to check the alignment of an equatorial telescope.
At 8:00 the Pleiades transit the meridian, meaning the famous star cluster is
then due south and highest in the sky.
Neptune sets at 8:24, so we can cross it
oﬀ our observing list for tonight.
Jupiter rises in the east at 9:32 p.m.
The Great Orion Nebula (Messier 42)
transits the meridian at 9:48, as does
Sirius at 10:58. Transits of celestial
landmarks help indicate when they are
best placed for viewing, and where the
constellations are during the night.
Running vertically down the midnight line is a scale of hours. This shows
the sidereal time (the right ascension of
objects on the meridian) at midnight. On
January 17-18 this is 7h 48m. To ﬁnd the
sidereal time at any other time and date
on the chart, locate that point and draw a
line through it parallel to the white event
lines of stars. See where your line intersects the sidereal-time scale at midnight.
(A star's event line enters the top of the
chart at the same time of night it leaves
the bottom. Sometimes one of these seg-

ments is left out to avoid crowding.)
Near the midnight line is a white
curve labeled Equation of time weaving
narrowly right and left down the chart.
If you regard the midnight line as noon
for a moment, this curve shows when
the Sun crosses the meridian and is due
south. On January 17th the Sun runs
slow, transiting at 12:10 p.m. This variation is caused by the tilt of Earth's axis
and the ellipticity of its orbit.
Mars rises at 1:16 a.m., a sign it will
be in ﬁne view later this year. Then at
1:49 we see a Moon symbol, and the
legend at the chart's bottom tells us it is
at waxing gibbous phase, and setting.
(So the night until now has been brightly
moonlit.) Jupiter reaches its high point
in the sky at 3:48. Then at 4:08 the ringed
planet Saturn rises in the east, followed
in 8 minutes by Antares, a star we usually associate with a much later season.
Brilliant Venus rises in a dark sky at
4:58 a.m. The ﬁrst hint of dawn - the
start of morning twilight - comes at
5:44. The Sun ﬁnally peeks above the
horizon at 7:19 a.m. on January 18th.

Other Charted Information
Many of the year's chief astronomical
events are listed in the chart's evening
and morning margins. Some are marked
on the chart itself.
Conjunctions (close pairings) of two
planets are indicated on the chart by a
symbol on the planets' event lines.
Here, conjunctions are considered to
occur when the planets actually appear
closest together in the sky (at appulse),
not merely when they share the same
ecliptic longitude or right ascension.
Opposition of a planet, the date when
it is opposite the Sun in the sky and thus
visible all night, occurs when its transit
line crosses the Equation-of-time line
(not the line for midnight). Opposition
symbol, as for
is marked there by a

Sky and Telescope - January 2016

Table of Contents for the Digital Edition of Sky and Telescope - January 2016