Sky & Telescope - January 2025 - SGA2

Almanac 2025
Skygazer's
30°S
What's in the
sky tonight?
When does the Sun set, and when does
twilight end? Which planets are visible?
What time is moonrise?
Welcome to the Skygazer's Almanac
2025, a handy chart that answers these
and many other questions for every night
of the year. This version is plotted for
skywatchers near latitude 30° south -
in Australia, southern Africa, and the
southern cone of South America.
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 5, 2025.
First find " January " and " 5 " 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 5-6 crosses
SGA25S
F OR LAT I T UD ES NE AR 30° SOUTH
many slanting event lines. Each event line
tells when something happens.
The dotted line for January 5-6 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 5th occurs at 7:05 p.m.
Local Mean Time. (All times read from the
chart are Local Mean Time, which can
differ from your civil clock time by many
minutes. More on this later.)
Continuing rightward on the dotted
line for the 5th, we see a Mars Rises line
crossing it at 8:10 p.m. This lets us know
the red planet will be up all night long.
Evening twilight doesn't truly end until
8:41, when the Sun is 18° below the horizon
(note the dashed line).
At 8:47 the Pleiades star cluster
transits the meridian, its high point in
the sky. Moving to the right we see that
Jupiter transits at 9:44, so it, too, is well
situated as an observing target. But brilliant
Venus, the fabled " evening star, "
sets four minutes later.
At about 10:22 the Large Magellanic
Cloud culminates (another way of saying
it transits). The Great Orion Nebula,
Messier 42, transits at 10:35, and the two
brightest nighttime stars, Canopus and
Sirius, transit at 11:23 and 11:44, respectively.
Transit times of such celestial landmarks
help us follow the nightly march of
constellations.
At about 10:51, notice the tiny Moon
symbol on the dotted line. The legend at
the bottom of the chart tells us it is at its
waxing crescent phase, setting.
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 5-6 this is 7h 02m. 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 north. On January 5th the
Sun runs slow, transiting at 12:05 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 1:12 a.m. the red planet Mars
transits, the very best time to spot its
surface details in a good telescope. As the
wee hours continue, Antares, a star we
usually associate with later seasons of
the year, climbs above the southeastern
horizon at 2:19.
The first hint of dawn - the start of
morning twilight - comes at 3:31. Elusive
Mercury rises at 3:42. The Sun finally
peeks above the southeastern horizon at
5:06 on Monday morning, January 6th.
Other Charted Information
Many of the year's most important
astronomical events are listed in the
Local Mean Time Corrections
Adelaide
Brisbane
Canberra
+16
-13
+4
Cape Town +46
Durban
Harare
Asunción
-3
-4
-10
Buenos Aires +54
Montevideo +45
Melbourne
Perth
Sydney
+20
+18
-4
Johannesburg +8
Port Elizabeth +18
Pretoria
+8
Rio de Janeiro -7
Santiago
São Paulo
+43
+6
Sky & Telescope - January 2025

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