Sky and Telescope - January 2016 - S11

Skygazer's
Almanac 50°N

FOR LATITUDES
NEAR 50° 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. This version is plotted for
skywatchers near latitude 50° north - in
the United Kingdom, northern Europe,
Canada, and Russia.
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
SGA16E

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 4:29 p.m. Local Mean Time. (All times
on the chart are Local Mean Time, which
can diﬀer from your standard clock time
by many minutes. More on this later.)
Moving to the right, we see that
the bright star Sirius rises at 6:19 p.m.
Evening twilight ends at 6:24, marking
the time when the Sun is 18° below the
horizon and the sky is fully dark.
At 7:06 p.m. Polaris, the North Star,
reaches upper culmination. This is when
Polaris stands directly above the north
celestial pole (by 40′ this year), a good
opportunity to check the alignment of an
equatorial telescope.
The Pleiades transit the meridian
at 8:01 p.m., followed by the famous
Orion Nebula at 9:49 and Sirius at 10:59.
Transits of celestial landmarks mark
their high points in the sky and remind
us where constellations are throughout
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 7 h 47m. To ﬁnd
the sidereal time at any other time and
date on the chart, locate the point for
the time and date you want, then 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 the
previous 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 around the Sun.
Mars rises at 1:35 a.m., a sure sign it
will become prominent in the evening
sky later this year. Then near 1:51 we see
a Moon symbol, and the legend at the
chart's bottom tells us it is at gibbous
phase, setting. (That is, we've had bright
moonlight this evening up to now.)
Jupiter transits at 3:49 a.m., an ideal
time to check on its moons and cloud
belts with a telescope. The ringed planet
Saturn rises at 4:42, and then a star we
usually associate with a later season,
Antares, comes up at 5:03. Brilliant
Venus appears at 5:32.
The ﬁrst hint of dawn - the start of
morning twilight - comes at 5:55 a.m.
The Sun ﬁnally peeks above the eastern
horizon at 7:51 a.m. on the morning of
January 18th.

Local Mean Time Corrections
Amsterdam
Belfast
Berlin
Bordeaux
Bremen
Brussels
Bucharest
Budapest
Calgary
Copenhagen
Dublin
Geneva
Glasgow
Halifax
Hamburg
Helsinki
Kiev
London
Lyons

+40
+24
+6
+62
+24
+44
+16
-16
+36
+10
+25
+35
+16
+14
+20
+20
-2
0
+41

Manchester
Montreal
Moscow
Munich
Oslo
Ottawa
Paris
Prague
Quebec
Regina
Reykjavik
St. John's
Stockholm
Toronto
Vancouver
Vienna
Warsaw
Winnipeg
Zurich

+8
-6
+26
+14
+17
+3
+51
+2
-15
+58
+88
+1
-12
+18
+12
-5
-24
+29
+24

Sky and Telescope - January 2016

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