light from Uranus can interfere with
such dim targets, so you may want to
use an occulting bar to hide the planet.
Use a charting program and the Sky &
Telescope Moons of Uranus observing
tool (https://is.gd/UranusMoons) to
plan your search.
Unlike Uranus, which is fairly easy
to fi nd, Neptune requires a telescope
(or large binos) and patience to see.
Neptune began peeking over the eastern
horizon in late March, rising with
Aquarius in morning twilight. By the
June solstice, it was reasonably well-
placed for observation, though still a
morning target. At the beginning of
July, Neptune eased into the nighttime
sky, and now, as it approaches opposi-
tion on the night of September 9–10, is
perfectly positioned for evening view-
ing. On the night of September 5–6,
with best views after local midnight,
Neptune passes just 13′′ from 4th-
magnitude Phi (φ) Aquarii. Neptune’s
largest moon, Triton, comes even closer
to the star. If you don’t like star-hops,
this is the night to let your Go To scope
take you to Phi.
The difference between planet,
moon, and star should be apparent in
the eyepiece, even at low magnifi ca-
tions. At magnitude 7.8, Neptune shines
more dimly than Phi but has a steadier,
less “twinkly” light. A medium-aperture
scope will reveal Neptune’s 2.4′′ disk
and perhaps a hint of blue-gray. Triton,
on the other hand, remains a speck
compared to the other members of this
trio, and seeing it under the best of cir-
cumstances can be diffi cult. Look for a
modest 13.5-magnitude gray-white dot.
Use the Sky & Telescope Triton Tracker
(https://is.gd/TritonTracker) to help
locate the tiny moon and let us know if
you fi nd it!
On the night of June 21–22, Nep-
tune reached its easternmost point and
began retrograde motion. The ice giant
will continue to travel westward until
November 27th, when it resumes pro-
grade (eastward) travel.
skyandtelescope.com • SEPTEMBER 2019 49
June 1, 2019July 1Aug 1Sept 1
Oct 1
Nov 1
Dec 1
Jan 1, 2020Feb 1Mar 1ξ+14°+12°+10°2 h 20 m 2 h 10 m 2 h 00 m
Path(^) of (^) U
ranu
s
St
ar
m
ag
ni
tu
de
s 5 6 7 8 9
ARIES
CETUS PISCES
May 1, 2019
Pat
h (^) o
f (^) Ne
ptu
ne
June 1
July 1
Aug 1
Sept 1
Oct 1
Nov 1 Dec 1
Jan 1, 2020
Feb 1
r
q
83
23 h 30 m 23 h 20 m 23 h 10 m
–8°
–6°
–4°
AQUARIUS
St
ar
m
ag
ni
tu
de
s 4
5
6
7
8
9
Algol
18
21
29
30
38
PERSEUS
TRIANGULUM
34
pWith the arrival of autumn in the Northern
Hemisphere, Perseus climbs the northeastern
sky in the evening. Every 2.7 days, Algol (Beta
Persei) dips from its usual magnitude 2.1 to 3.4
and back. Use this chart to estimate its bright-
ness with respect to the convenient compari-
son stars of magnitude 2.1 (Gamma Androme-
dae) and 3.4 (Alpha Trianguli).
Aug. UT Sept. UT
3 20:22 1 12:28
6 17:11 4 9:17
9 14:00 7 6:05
12 10:48 10 2:54
15 7:37 12 23:43
18 4:25 15 20:31
21 1:14 18 17:20
23 22:02 21 14:08
26 18:51 24 10:57
29 15:40 27 7:46
30 4:34
These geocentric predictions are from the
recent heliocentric elements Min. = JD
2445641.554 + 2.867324E, where E is any
integer. For a comparison-star chart and
more info, see skyandtelescope.com/algol.
Minima of Algol
FIND YOUR CLUB:
skyandtelescope.com/astronomy-
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