Sky & Telescope - January 2022 - SA5

Almanac 2022
Skygazer's
40°N
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
2022, 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, the 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 9, 2022.
First find " January " and " 9 " 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 9-10 crosses
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F OR L A T I TUDE S N E AR 4 0 ° NOR T H
many slanting event lines. Each event line
tells when something happens.
The dotted line for January 9-10
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 9th occurs
at 4:53 p.m. Local Mean Time. (All times
on the chart are Local Mean Time, which
can differ from your clock time. More on
this later.)
We see that Venus sets at 5:01 p.m., so
soon after the Sun that we won't see it at
all. But Mercury sets in near darkness at
6:25, so it is well worth looking for until
that time. It is far from the Sun during
this current apparition, as described in
the column of text left of the chart.
At 6:29 a dashed line shows that twilight
technically ends. This is when the
Sun is 18° below the horizon and the sky
is fully dark.
The ringed planet Saturn sets at 6:45,
so we can cross it off tonight's observing
agenda. But dim Uranus transits the
meridian at 7:16, meaning it is due south
and " riding high, " an excellent time to
look for it in binoculars.
At 7:42 Polaris, the North Star, has
its upper culmination. It then stands
directly above the north celestial pole (by
38′ or 39′ this year), a good time to check
the alignment of an equatorial telescope.
The bright planet Jupiter sets at 8:24.
The famous Pleiades star cluster transits
at 8:30 p.m., followed by the Orion
Nebula (10:18) and Sirius (11:27). Transit
times of such celestial landmarks help us
keep track of the march of constellations
across the night sky.
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 9-10 this is 7h 19m. 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 segments
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 9th the Sun runs
slow, transiting at 12:07 p.m. This deviation,
important for reading a sundial, is
caused by the tilt of the Earth's axis and
the ellipticity of its orbit.
At 12:45 a.m. a small Moon symbol
appears on the dotted line, and we can
tell from the legend at the bottom of the
chart that it is at waxing gibbous phase,
setting. The wee hours continue, and at
4:46 Antares rises. This is a star we usually
associate with a much later season.
The first hint of dawn - start of
morning twilight - comes at 5:45 a.m.
Then the brilliant planet Venus rises at
6:51. The Sun finally peeks above the
horizon at 7:21 a.m. on January 10th.
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 by a symbol on
the planets' event lines. Here, conjunctions
are considered to occur when the
planets actually appear closest in the sky,
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 roughly when its
transit line crosses the Equation-of-time
Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022
