Sky & Telescope - January 2025 - SGA9

morning twilight - comes at 6:00. Elusive
Mercury rises at 6:40. The Sun finally
peeks above the eastern horizon at 7:58
a.m. on Monday morning, January 6th.
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 marked 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
visible all night, occurs roughly when its
transit line crosses the Equation-of-time
line (not the line for midnight). Opposition
is indicated there by a symbol.
For instance, Mars reaches opposition on
the night of January 15-16 this year.
Moonrise and moonset can be told
apart by whether the round limb - the
outside edge - of the Moon symbol faces
right (waxing Moon sets) or left (waning
Moon rises). Or follow the nearly
horizontal row of daily Moon symbols
across the chart to find the word Rise or
Set. Quarter Moons are indicated by a
larger symbol. Full Moon is always a large
bright disk whether rising or setting; the
circle for new Moon is open. P and A
mark dates when the Moon is at perigee
and apogee (nearest and farthest from
Earth, respectively).
Mercury and Venus never stray far
from the twilight bands. Their dates of
greatest elongation from the Sun are
shown by ◗ symbols on their rising or
setting curves. Asterisks mark the dates
when their disks in telescopes show the
greatest illuminated extent in square
arcseconds. For example, during February
evenings Venus does so on the 14th and
Mercury on 28th.
Meteor showers are marked by a starburst
symbol at the date of peak activity
and the time when the shower's radiant
is highest in the night sky. This is often
just as twilight begins before dawn.
Julian dates can be found from the
numbers just after the month names on
Rising or Setting Corrections
Declination (North or South)
0°
60° 1 11 23 36
55° 0
50° 0
45° 0
40° 1
5 10
4
8
8
15
35° 1 10 20
30° 1 12 25
25° 1 15 30
5° 10° 15° 20° 25°
53 80
23 32
16
13
23
31
39
46
18 24
32 43
44 68
54 72
64 84
the chart's left. The Julian Day, a sevendigit
number, is a running count of days
beginning with January 1, 4713 BC. Its
first four digits early this year are 2460,
as indicated just off the chart's upper left
margin. To find the last three digits for
evenings in January, add 676 to the date.
For instance, on the evening of January
5th we have 5 + 676 = 681, so the
Julian Day is 2,460,681. For European
observers this number applies all night
long, because the next Julian Day always
begins at 12:00 Universal Time (noon
Greenwich Mean Time).
Time Corrections
All events on this Skygazer's Almanac are
plotted for an observer at longitude 0°
and latitude 50° north, a reasonable
compromise for the countries of northern
and central Europe. However, you
need not be on a boat in the English
Channel to use the chart. Simple corrections
will allow you to get times accurate
to a couple of minutes anywhere in the
world's north temperate latitudes.
To convert the charted time of an
event into your civil (clock) time, the
following corrections must be made.
They are given in order of decreasing
importance:
* Daylight-saving time (or " summer
time " ). When this is in effect, add one
hour to any time that you obtain from
the chart.
* Your longitude. The chart gives the
Local Mean Time (LMT) of events, which
differs from ordinary clock time by a
number of minutes at most locations.
Our civil time zones are standardized
on particular longitudes. Examples in
Europe are Greenwich Mean Time (or
Universal Time), 0°; Central European
Time, 15°E; and Eastern European Time,
30°E. If your longitude is very close to one
of these (as is true for London), luck is
with you and this correction is zero. Otherwise,
to get standard time add 4 minutes
to times obtained from the chart for each
degree of longitude that you are west of
your time-zone meridian. Or subtract 4
minutes for each degree you are east of it.
For instance, Copenhagen (longitude
12.5° east) is 2.5° west of the Central
European Time meridian. So at Copenhagen,
add 10 minutes to any time obtained
from the chart. The result is Central
European Standard Time.
Find your local-time correction and
memorize it. In the table below at left are
the corrections from local to standard
time, in minutes, for some major cities.
* Rising and setting. Times of rising
and setting need correction if your latitude
differs from 50° north. This effect
depends strongly on a star or planet's
declination. (The declinations of the Sun
and planets are listed in Sky & Telescope.)
If your site is north of latitude 50°,
then an object with a north declination
stays above the horizon longer than
the chart shows (it rises earlier and sets
later), while one with a south declination
spends less time above the horizon.
At a site south of 50°, the effect is just
the reverse. Keeping these rules in mind,
you can gauge roughly the number of
minutes by which to correct a rising or
setting time from the table above.
Finally, the Moon's rapid orbital
motion alters lunar rising and setting
times slightly if your longitude differs
from 0°. The Moon rises and sets about
two minutes earlier than the chart
shows for each time zone east of Greenwich
Mean Time, and two minutes later
for each time zone west.
For reprints (item SGA25E) or to order a
similar chart for latitude 40° north or 30° south, go
to: shopatsky.com/collections/maps-globes/almanacs
Skygazer's Almanac 2025 is a
supplement to Sky & Telescope
Magazine, 1374 Massachusetts
Avenue, Cambridge, MA 02138,
USA, skyandtelescope.org.
©2024 AAS Sky Publishing,
LLC. All rights reserved.
North Latitude
http://www.shopatsky.com/collections/maps-globes/almanacs http://www.skyandtelescope.org
Sky & Telescope - January 2025

Table of Contents for the Digital Edition of Sky & Telescope - January 2025
