Sky & Telescope - January 2025 - SGA6

transit line crosses the Equation-of-time
line (not the line for midnight). Opposition
is marked there by a symbol, as
for Mars on the night of January 15-16.
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 their dates of greatest
illuminated extent in square arcseconds.
For example, this occurs for Venus on the
evening of February 14th this year.
Meteor showers are marked by a starburst
symbol on the date of peak activity
and at the time when the shower's radiant
is highest in the night sky. This is
often just as morning twilight begins.
Julian dates can be found from the
numbers just after the month names on
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 most of 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 North
American observers this number applies
all night, because the next Julian Day
always begins at 12:00 Universal Time
(6:00 a.m. Central Standard Time).
Time Corrections
All events on this Skygazer's Almanac are
plotted for an observer at longitude 90°
west and latitude 40° north, near the
population center of North America.
However, you need not live near Peoria,
Illinois, to use the chart. Simple corrections
will allow you to get times accurate
to a couple of minutes anywhere in
Rising or Setting Corrections
Declination (North or South)
50°
45°
40°
35°
30°
25°
0°
5° 10° 15° 20° 25°
14 23 32 43
10 14 19
9
7
3
3
5
8
7
6
12 16
11 16 23 30
16 24 32 42
the world's north temperate latitudes.
To convert the charted time of an
event to your civil (clock) time, the following
corrections must be made. They
are mentioned in order of decreasing
importance:
* Daylight-saving time. When this
is in effect, add one hour to any time
obtained 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
North America are Eastern Time, 75°W;
Central, 90°; Mountain, 105°; and
Pacific, 120°. If your longitude is very
Local Mean Time Corrections
Atlanta
Boise
Boston
Buffalo
Chicago
Cleveland
Dallas
Denver
Detroit
El Paso
Helena
Honolulu
Houston
+38
+45
-16
+15
-10
+27
+27
+32
+6
+28
+31
+21
Indianapolis +44
Jacksonville +27
Kansas City +18
Athens
Baghdad
Beijing
Belgrade
Cairo
Istanbul
Jerusalem
+25
+3
+14
-22
-8
+4
-21
Los Angeles
Memphis
Miami
New York
Pittsburgh
St. Louis
-7
+21
Minneapolis +13
New Orleans
-4
Philadelphia +1
Phoenix
+28
+20
+1
Salt Lake City +28
San Francisco +10
Santa Fe
Seattle
Tulsa
Washington
Lisbon
Madrid
New Delhi
Rome
Seoul
Tehran
Tokyo
+4
+9
+24
+8
+36
+75
+21
+10
+32
+4
-19
close to one of these (as is true for New
Orleans and Denver), 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, Washington, DC (longitude
77°), is 2° west of the Eastern Time
meridian. So at Washington, add 8 minutes
to any time obtained from the chart.
The result is Eastern Standard Time.
Find your time adjustment and memorize
it. The table below left shows the
corrections from local to standard time,
in minutes, for some major cities.
* Rising and setting. These times
need correction if your latitude differs
from 40° north. This effect depends
strongly on a star or planet's declination.
(The declinations of the Sun and planets
are listed monthly on the Planetary
Almanac page of Sky & Telescope.)
If your site is north of latitude 40°,
then an object with a north declination
stays above the horizon longer than
the chart shows (it rises earlier and sets
later), whereas one with a south declination
spends less time above the horizon.
At a site south of 40°, the effect is just
the reverse. Keeping these rules in mind,
you can gauge the approximate number
of minutes by which to correct a rising or
setting time from the table above.
Finally, the Moon's rapid orbital
motion affects lunar rising and setting
times if your longitude differs from 90°
west. The Moon rises and sets about two
minutes earlier than the chart shows
for each time zone east of Central Time,
and two minutes later for each time zone
west of it. European observers can simply
shift each rising or setting Moon symbol
leftward a quarter of the way toward the
one for the previous night.
For reprints (item SGA25W) or to order a similar
chart for latitude 50° 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

https://shopatsky.com/collections/maps-globes/almanacs https://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