Sky & Telescope - February 2025 - 50

FEBRUARY 2025 OBSERVING
Celestial Calendar
Action at Jupiter
Zodiacal Light Nights
THE SOLAR SYSTEM'S salt and pepper
- spent comet dust, crumbs from
asteroids, and even dust from Mars
- all contribute to the gritty granularity
of the zodiacal light. From Earth,
the trillions of tiny grains (sized from
0.001 mm to 0.300 mm) look like the
myriad distant stars of the Milky Way
scrunched together into a luminous
haze. In truth, however, each zodiacallight
particle is spaced several kilometers
from the next.
From about February 13 to 22, when
the Moon is absent from the evening
sky, Northern Hemisphere observers
get to see the zodiacal light at its best.
The wedge-shaped glow is broadest and
brightest at its base near the western
horizon. From there it gradually tapers
and becomes more and more attenuated
with altitude. Under exceptionally dark
skies, the wedge narrows to a cone that
extends high into the southern sky and
Minima of Algol
Jan.
UT
2
5
8
10
13
16
19
22
25
28
31
7:53
4:42
1:31
22:21
19:10
15:59
12:49
9:38
6:27
3:17
0:06
Feb.
2
5
8
11
14
17
20
22
25
28
continues eastward as the extremely
faint zodiacal band.
The zodiacal light is named for the
zodiac, the belt of sky centered on the
ecliptic. The dust that produces the glow
is concentrated in a pancake-like disk
that extends out to beyond the orbit of
Mars. From February through April, the
ecliptic meets the western horizon at
dusk at a steep angle, tipping the zodiacal
light into good view for observers at
mid-northern latitudes.
The bottom of the cone measures
about 20° across near its base, while its
apex reaches altitudes of 45° to more
than 80°, depending on sky conditions.
Since the zodiacal light follows the
ecliptic, it slants southward like a wispy
Leaning Tower of Pisa.
Look for the ghostly glow towering in
the west starting about 90 minutes after
sunset. It slowly sinks in the west over
the next 90 minutes.
JUPITER IS NOW solidly an eveningsky
target, transiting the meridian on
the 1st of the month about 2½ hours
after sunset. That means it's at its best
at a convenient hour for most observers.
By the time midnight rolls around,
Jupiter's altitude has dropped from
its maximum of 72° to about 35°, for
those at mid-northern latitudes. By the
end of February, the planet transits just
a few minutes after sunset. During the
month, the Jovian disk shrinks slightly
from 43.4″ to 39.7″ while it dims imperceptibly
from magnitude -2.5 to -2.3.
The bottom line is this shortest month
of the year is a fine one for training
your telescope on the solar system's
most dynamic planet.
Even the smallest of telescopes
reveals the four big Galilean moons,
and binoculars usually show at least
two or three. The moons orbit Jupiter
at different rates, changing positions
along an almost straight line from
our point of view on Earth. Use the
diagram on the facing page to identify
them by their relative positions on any
given date and time. All the observable
interactions between Jupiter and its
satellites and their shadows are tabulated
on the facing page. Find events
timed for when Jupiter is at its highest.
Features on Jupiter appear closer to
UT
29
20:55
17:45
14:34
11:24
8:13
5:02
1:52
22:41
19:30
16:20
These geocentric predictions are from the recent
heliocentric elements Min. = JD 2457360.307
+ 2.867351E, where E is any integer. They were
derived by Roger W. Sinnott from 15 photoelectric
series in the AAVSO database acquired
during 2015-2020 by Wolfgang Vollmann, Gerard
Samolyk, and Ivan Sergey. For a comparison-star
chart and more info, see skyandtelescope.org/algol.
50 FEBRUARY 2025 * SKY & TELESCOPE
18
30
PERSEUS
38
Algol
21
the central meridian than to the limb
for 50 minutes before and after transiting.
Here are the times, in Universal
Time, when the Great Red Spot should
cross Jupiter's central meridian. The
dates, also in UT, are in bold. (Eastern
Standard Time is UT minus 5 hours.)
January 1: 1:55, 11:51, 21:46; 2:
TRIANGULUM
34
pPerseus is conveniently positioned at the
zenith during evening hours in February. Every
2.87 days, Algol (Beta Persei) dips from its
usual magnitude 2.1 to 3.4 and back. Use this
chart to estimate its brightness in respect to
comparison stars of magnitude 2.1 (Gamma
Andromedae) and 3.4 (Alpha Trianguli).
7:42, 17:37; 3: 3:33, 13:29, 23:24; 4:
9:20, 19:16; 5: 5:11, 15:07; 6: 1:03,
10:58, 20:54; 7: 6:49, 16:45; 8: 2:41,
12:36, 22:32; 9: 8:28, 18:23; 10: 4:19,
14:15; 11: 0:10, 10:06, 20:02; 12: 5:57,
15:53; 13: 1:49, 11:44, 21:40; 14: 7:36,
17:31; 15: 3:27, 13:23, 23:18; 16: 9:14,
19:10; 17: 5:05, 15:01; 18: 0:57, 10:52,
20:48; 19: 6:44, 16:39; 20: 2:35, 12:31,
22:26; 21: 8:22, 18:18; 22: 4:13, 14:09;
23: 0:05, 10:01, 19:56; 24: 5:52, 15:48;
25: 1:43, 11:39, 21:35; 26: 7:30, 17:26;
http://www.skyandtelescope.org/algol
Sky & Telescope - February 2025

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