Sky and Telescope - January 2017 - SGA17E

Skygazer's 50°N
Almanac
FOR L ATITUDES
NE AR 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
2017, 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 8, 2017.
First find "January" and "8" 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 8-9 crosses many
SGA17E

2017

slanting event lines. Each event line tells
when something happens.
The dotted line for January 8-9 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 8th occurs at 4:17 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
evening twilight ends at 6:15, marking
the time when the Sun is 18° below the
horizon and the sky is fully dark.
At 6:52 p.m. the bright star Sirius
rises. Then at 7:40 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 brilliant planet Venus, until now
prominent in the west, sets at 8:32. Two
minutes later the Pleiades star cluster
transits the meridian, followed by the
Orion Nebula, Messier 42, at 10:22.
Transits of celestial landmarks tell when
they are highest in the sky and remind us
where the constellations are all 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 8-9 this is 7h 15m. 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 8th the Sun
runs slow, transiting at 12:07 p.m. This
variation is caused by the tilt of Earth's
axis and the ellipticity of its orbit.
The giant planet Jupiter rises at 12:40
a.m., a sure sign it will be well placed
for telescopic study toward dawn. At
2:54 Regulus transits. Near 4:13 we see
a small 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 all night up to now.) Then
a star we usually associate with a later
season, Antares, rises at 5:35.
The first hint of dawn - the start of
morning twilight - comes at 5:59 a.m.
The elusive planet Mercury rises at 6:21,
early enough before sunup that we might
spot it as it climbs higher. The Sun finally
peeks above the eastern horizon at 7:56
a.m. on the morning of January 9th.

Other Charted Information
Many of the year's chief astronomical
events are listed in the chart's evening

Local Mean Time Corrections
Amsterdam +40
Belfast
+24
Berlin
+6
Bordeaux +62
Bremen
+24
Brussels
+44
Bucharest +16
Budapest
-16
Calgary
+36
Copenhagen +10
Dublin
+25
Geneva
+35
Glasgow
+16
Halifax
+14
Hamburg
+20
Helsinki
+20
Kiev
-2
London
0
Lyons
+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 2017

Table of Contents for the Digital Edition of Sky and Telescope - January 2017

Contents
Sky and Telescope - January 2017 - Cover1
Sky and Telescope - January 2017 - Cover2
Sky and Telescope - January 2017 - 1
Sky and Telescope - January 2017 - Contents
Sky and Telescope - January 2017 - 3
Sky and Telescope - January 2017 - 4
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Sky and Telescope - January 2017 - 84
Sky and Telescope - January 2017 - Cover3
Sky and Telescope - January 2017 - Cover4
Sky and Telescope - January 2017 - SGA17RAL
Sky and Telescope - January 2017 - 90
Sky and Telescope - January 2017 - SGA17R
Sky and Telescope - January 2017 - SGA17RA
Sky and Telescope - January 2017 - SGA17EAL
Sky and Telescope - January 2017 - 94
Sky and Telescope - January 2017 - SGA17E
Sky and Telescope - January 2017 - SGA17EA
Sky and Telescope - January 2017 - SGA17SAL
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Sky and Telescope - January 2017 - SGA17S
Sky and Telescope - January 2017 - SGA17SA
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